Compared to analog. Differences between digital and analog servos

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There are scientific papers (eg Chakrapani & Palem) and devices (eg Lyric) that use what is called probabilistic logic. I guess the idea is that the outputs of such a device, given some inputs, converge to some probability distribution. What is the difference between these devices and analog signals? So are these devices still considered digital, analog, mixed signal?

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This article appears to be describing a new (probabilistic) boolean logic, and it is not about implementation. I was just looking at the paper, but it looks like it's another one of those theories. There is, by the way, a simple reason why probabilistic logicians don't give you what classical logicians give you, namely, they are not truth functional (i.e. the value of A & B does not depend solely on the value of A and the value of B).

As for implementing such a thing on a chip: I think both are possible. If you do it digitally, then you're calculating probabilities, and you might as well run some code on the processor. I don't really know about analog implementations, but I think any basic analog component (transistor, operating system etc.) can be considered as performing some basic arithmetic operation by voltages and currents. Whether the pattern produces conclusions that adhere to or approximate Kolmogorov's laws of probability is another question, but I assume it is possible, and perhaps it has been done.

The use of digital technologies in CCTV is constantly increasing. Let's look at the differences between digital and analog television.
The beginning and end of any process is an analog signal. Intermediate values ​​can be converted to digital format, which provides many advantages. Human sensory organs (ear, eye, nose, skin, etc.) respond only to a continuous analog signal.

Analogue systems

An analog signal is a continuous electrical voltage signal that represents a physical process, like light, sound, or any other variable. Although the analog process is easier to understand, it has many limitations.

Noise and Interference

All electronic circuits and devices produce some amount of random noise. In addition, there is also external electromagnetic interference. Since an analog signal is a continuous function, this noise and interference becomes part of the signal and cannot be completely eliminated. Noise components increase with the number of electrical circuits.

Distortions

An analog signal depends on the proportionality between a physical process and its corresponding electrical voltage. Most analog circuits are nonlinear, meaning that the output signal does not exactly match the input signal. Usually this position cannot be completely corrected. Moreover, in a large system these distortions accumulate. In all analog circuits, small changes in signal level occur as a result of external factors, such as temperature changes. They cannot be corrected because they are inseparable from the signals themselves.

Digital systems

The digital system is more complex, but it has many advantages over the analog system.

Accurate representation

Once an analog signal is converted to a digital signal, its parameters can be maintained unchanged throughout the system, regardless of its size (except when compression is used). This occurs due to the digital system's immunity to external noise and interference.

Signal transmission without loss of information

All signal transmission systems are primarily analog and have inherent noise and distortion problems. However, digital signals can be protected against errors, allowing digital signals to be transmitted without distortion.

Process complexity

In an analog system, each step in a complex signal processing process typically requires a separate circuit. In a digital system one CPU(CPU) can be programmed so that using appropriate software it can carry out various steps. This allows the digital system to handle many more processes.

Low cost

Integrated circuits (ICs) for digital systems are much cheaper to produce than for analog systems.

Digital storage was one of the first uses of digital video. Digital video signals can be stored in memory with quick search. This memory also makes it possible to display signals in different formats, regardless of the incoming signal format. It is possible to display signals with different resolutions and formats (PAL, NTSC, etc.).

Disadvantages of digital video systems

• More difficult to understand and design
• Requires wider bandwidth (however, various methods compression overcomes this disadvantage).
• There is no gradual deterioration of a digital signal - even a small error can distort the entire image.

Translation: Y.M.Gedzberg

The main disadvantages of digital systems for transmitting, processing and storing audio signals include:

1) extension of the frequency band. Transmission of analog signals requires a frequency band that is no greater than the bandwidth of the original signal. The need to expand the bandwidth for the passage of digital signals is determined by the fact that samples are represented in the form of binary code combinations, during the transmission of which each bit of the code combination is displayed as a separate pulse. Therefore, one of the main disadvantages of the digital representation of signals is the high requirements for the bandwidth of communication channels and the capacity of storage devices;

2) analog-to-digital conversion. When implementing ADCs, they strive to find a compromise between the accuracy of the original signal representation in digital form, which is achieved by increasing the number of quantization levels and sampling rates, and the degree of bandwidth expansion required to transmit the digital signal, or the storage capacity required to store it. It is common practice to ADC audio signals with sufficient high degree accuracy (about 16 bits per 1 sample) with a subsequent reduction in the number of bits per sample by using various digital compression schemes;

3) the need for time synchronization. Synchronization determines the times at which an incoming signal must be counted in order to decide what value has been transmitted. For optimal signal detection, the pulse generator must be synchronized with the timing of the pulses arriving from the line. The problem is aggravated in cases where the network is formed by several switching stations and it is necessary to solve problems of internal and network-wide synchronization;

4) incompatibility with existing analog devices. Digital equipment that is used, for example, in local telephone networks, necessarily provides a standard analog "interface" with the rest of the network. Therefore, until all networks are fully digital, it will be virtually impossible to achieve the maximum benefits of digital telephone systems in terms of signal quality and the provision of “non-voice” services.

The main technical advantages of digital systems for processing, transmitting and storing audio signals are as follows:

1) the possibility of signal regeneration. The main advantage of a digital system is that the probability of an error occurring in the linear path when transmitting a message can be made very small by introducing regenerators at intermediate points of the transmission lines. Intermediate nodes will detect and regenerate digital signals before the distortion occurring in the channel reaches a level that will lead to reception errors, i.e. the influence of these distortions is excluded. In contrast, in analog systems, noise and distortion accumulate as the signal passes from one site to another. If the number of regeneration points in the designed digital communication system is sufficient to eliminate errors in the channel, then the quality of transmission in the communication network is determined only by the process of converting the signal into digital form, and not by the transmission system;

2) the ability to work at low values ​​of the signal-to-noise ratio (interference). Noise and interference during the transmission of audio signals in analog networks are most pronounced during pauses, when the signal amplitude is small. Another of the main problems in the design and operation of analog networks, for example, in telephony, is the need to eliminate transient interference between the circuits through which speech is transmitted. The problem becomes even more acute during those periods when there is a pause in the conversation in one channel, and the other, influencing channel is transmitting a signal at maximum power level. In digital systems, during pauses, certain code combinations are transmitted, and the power level of the signals transmitted during pauses is the same as during transmission useful information. Since signal regeneration during digital transmission eliminates almost all noise arising in the transmission medium, the noise of a free channel (during a pause) is determined only by the encoding process, and not by the transmission line. Thus, pauses are not defined maximum levels noise, as is the case in analog systems, and low-level transient interference is eliminated during the regeneration process in digital regenerators or receivers.

Digital transmission lines provide the possibility of virtually error-free transmission of messages over communication channels with signal-to-noise ratio values ​​of the order of 15-25 dB, depending on the coding method (the accepted value of the signal-to-noise ratio when transmitting from one terminal device to another in an analog network is 46 and 40 dB, respectively, for local and international communication lines), which ensures the competitiveness of digital systems in comparison with analogue ones when used in conditions of low received signal levels and the presence of transient interference;

3) ease of transfer of control information. The control information is predominantly digital in nature and can therefore be easily incorporated into a digital transmission system. Regardless of the method of introducing control information into the digital path (time division multiplexing, introducing special control code combinations), in relation to the transmission system, control information turns out to be indistinguishable from information messages. In contrast, analogue transmission systems have fewer, often very limited, capabilities for transmitting control information, which has led to the emergence of many different types of control signal formats and the need to design devices for recognizing and converting these formats;

4) adaptability to other types of services. The use of an analog network, for example, a telephone network, to organize other types of communication not intended for the transmission of voice information may require special measures to adapt to the conditions of speech signal transmission (in particular, to comply with a frequency band of up to 4 kHz). On the contrary, in a digital system, any message has a standard format accepted in the transmission system. Thus, the transmission system does not have to analyze the type of information being transmitted and can be generally indifferent to the nature of the load it serves;

5) digital signal processing. Signal processing usually refers to such operations on signals that improve or transform their characteristics. The main advantages of digital signal processing are as follows:

Programmability. One basic structure with a variable algorithmic or parametric description in digital memory can be used for signal processing various types;

Sharing. A single digital signal processing device can be used to process many signals by storing the intermediate results of each process in a random access memory (RAM) and processing the signal sequence in some cyclic time-sharing manner;

Automatic control. Since digital data is used at the inputs and outputs of a digital signal processing device, the correct operation of the device can be checked in a standard way by comparing the response at its output to a certain test sequence of data recorded in the memory;

Versatility. Because digital signal processing is implemented by digital logic circuits, the processing process can involve many different functions that might not be possible or impractical to implement in analog form.

Examples of operations related to signal processing and implemented more efficiently in digital processing are: detection (generation) of certain frequencies, amplification (attenuation), correction, filtering, companding, conversion of various message formats;

6) Ease of group formation. The essence of group formation methods (multichannel signal transmission) is that messages from various sources of information are combined to form a group signal, which is transmitted over the communication line. When using analog communication systems, the principle of frequency division of channels (FDM) is usually used, in which each channel of the system is provided with a certain section of the frequency range, the width of which is equal to or greater than the frequency band of the subscriber channel. In digital multichannel communication systems, usually built on the principle of time division of channels (TDDC), signals are transmitted alternately along the communication line from various message sources using the full frequency bandwidth of the linear path during the transmission of signals from each source.

FDM equipment is usually more expensive than TDM equipment, even when the cost of analog-to-digital conversion is taken into account. It should be noted that the formation of group analog signals with TRC is also quite simply implemented, however, the disadvantage of analog systems with TRC is their low noise immunity, due to the susceptibility of narrow analog pulses to interference, distortion, crosstalk and intersymbol interference;

7) ease of classification. Unlike analog messages, the encryption of which is a rather labor-intensive task, and the reliability of the encryption is often insufficient, the implementation of scrambling and descrambling of a digital stream is more simple and efficient.

Many of the advantages of digital transmission (over analogue) can also be attributed to digital recording. The first of these advantages is the ability to determine the quality of playback during recording and maintain this quality indefinitely by periodically copying (regenerating) digitally recorded information, which is not possible with analog recording.

Another advantage of digital storage systems is the ability to use low-quality (non-linear) recording media with a lower signal-to-noise ratio compared to analog media. As a result, digital playback devices will become economically attractive to consumers due to the reduction in the cost of electronic products and recording media.

8) Analysis and synthesis of audio signals, especially speech, is an area of ​​widespread research closely related to the conversion of speech into digital form. Some of the speech encoders and decoders operating at the lowest bit rates involve some degree of analysis and synthesis of speech signals in digital form.

9) high reliability and degree of integration with other devices (primarily digital ones), ease of interfacing with a computer.

The introduction of DSP is occurring at a particularly rapid pace in various types of communications, in particular wireless. Such tools include digital switches for automatic telephone exchanges, speech recognition tools in voice control systems, speech encoding and channel multiplexing tools in telephone and cellular radiotelephone communication systems, image compression tools in video telephony, and information protection tools from unauthorized access. New technical requirements for 3G generation communication systems include the use of higher frequency ranges(2-3 GHz), expanding the bandwidth of channels and packets, high data transfer speeds (up to 2 Mbit/s). New generation mobile terminals must provide full Internet access with the ability to exchange audio/video information.

Accelerators based on digital signal processors (DSP) increase computer performance by an order of magnitude or more, and in combination with analog input/output interfaces, they turn a PC into a workstation for solving problems in acoustics, radar, television and radio broadcasting, medicine, etc. In many ways, it is the capabilities of efficient processing speech, audio and video information in hardware circuits based on DSPs made it possible to make a qualitative leap in the use of computer technology.

Introduction

The purpose of this work is to consider the advantages of digital technology and their reasons.

Digital technologies, as such, rely on representing signals in discrete bands of analog levels rather than as a continuous spectrum. All levels within a band represent the same signal state.

Since the late 90s of the last century, it has been generally accepted that the future lies with digital technologies. In this work I will try to highlight the main reasons and theses of this point of view.

1. Analog signal

An analog signal is a data signal in which each of the representing parameters is described by a function of time and a continuous set of possible values. Such signals are described continuous functions time, which is why an analog signal is sometimes called a continuous signal.

The properties of analog signals largely reflect their continuity:

· The absence of clearly distinguishable discrete signal levels makes it impossible to apply the concept of information in the form as it is understood in digital technologies to describe it. The “amount of information” contained in one reading will be limited only by the dynamic range of the measuring instrument.

· No redundancy. From the continuity of the value space it follows that any noise introduced into the signal is indistinguishable from the signal itself and, therefore, the original amplitude cannot be restored. In reality, filtering is possible, for example, using frequency methods, if some Additional Information about the properties of this signal (in particular, the frequency band).

Consider this type of signal at simple example. During a conversation, our vocal cords emit a certain vibration of varying tonality (frequency) and volume (sound signal level). This vibration, having traveled a certain distance, enters the human ear, affecting there the so-called auditory membrane. This membrane begins to vibrate with the same frequency and strength of vibration that our sound cords emitted, with the only difference that the strength of vibration weakens somewhat due to overcoming the distance.

So, the transmission of voice speech from one person to another can safely be called analog signal transmission, and that's why.

The point here is that our vocal cords emit the same sound vibration that the human ear itself perceives (what we say is what we hear), that is, transmitted and received sound signal, has a similar pulse shape, and the same frequency spectrum of sound vibrations, or in other words, “similar” sound vibration.

Now, let's look at a more complex example. And for this example, let’s take a simplified diagram of a telephone, that is, the telephone that people used long before the advent of cellular communications.

During a conversation, speech sound vibrations are transmitted to the sensitive membrane of the handset (microphone). Then, in the microphone, the sound signal is converted into electrical impulses, and then travels through wires to the second handset, in which, using an electromagnetic transducer (speaker or earphone), the electrical signal is converted back into a sound signal.

In the above example, again, " analog» signal conversion. That is, sound vibration has the same frequency as the frequency of the electrical impulse in the communication line, and also, sound and electrical impulses have a similar shape (that is, similar).

In the transmission of a television signal, the analogue radio-television signal itself has a rather complex pulse shape, as well as a fairly high frequency of this pulse, because it is transmitted over long distances, as audio information, and video.

2. Digital signal

A digital signal is a data signal in which each of the representing parameters is described by a discrete time function and a finite set of possible values.

The signals are discrete electrical or light pulses. With this method, the entire capacity of the communication channel is used to transmit one signal. The digital signal uses the entire cable bandwidth. Bandwidthis the difference between the maximum and minimum frequency that can be transmitted over the cable. Each device on such networks sends data in both directions, and some can receive and transmit simultaneously. Narrowband systems transmit data as a digital signal of a single frequency.

A discrete digital signal is more difficult to transmit over long distances than an analog signal, so it must first be modulateon the transmitter side, and demodulate on the information receiver side. The use of algorithms for checking and restoring digital information in digital systems can significantly increase the reliability of information transmission.

It should be kept in mind that a real digital signal is analog in its physical nature. Due to noise and changes in the parameters of transmission lines, it has fluctuations in amplitude, phase/frequency of polarization. But this analog signal (pulse and discrete) is endowed with the properties of a number. As a result, it becomes possible to use numerical methods (computer processing) to process it.

For example, "digital signal", let’s take the principle of transmitting information using the fairly well-known “Morse code”. For those who are not familiar with this type of transmission of text information, I will briefly explain the basic principle below.

Previously, when signal transmission over the air (using a radio signal) was just developing, the technical capabilities of transmitting and receiving equipment did not allow transmitting a speech signal over long distances. Therefore, instead of speech information, text information was used. Since the text consists of letters, these letters were transmitted using short and long pulses of a tonal electrical signal.

This transmission of text information was called transmission of information using Morse code.

The tone signal, in its electrical properties, had a large throughput, than speech, and as a result, the range of the transmitting and receiving equipment increased.

The units of information in such signal transmission were conventionally called “dot” and “dash”. Short then new signal meant a dot, and a long tone meant a dash. Here, each letter of the alphabet consisted of a specific set of dots and dashes. For example, the letter Awas designated by the combination" .- " (dot-dash), and the letter B " - … "(dash-dot-dot-dot), and so on.

That is, the transmitted text was encoded using dots and dashes in the form of short and long segments of a tone signal. If the words “MORSE CODE” are expressed using dots and dashes, it will look like this:

The digital signal is based on a very similar principle of encoding information, only the units of information themselves are different.

Any digital signal consists of so-called “binary code”. Here, logical 0 (zero) and logical 1 (one) are used as units of information.

If we take an ordinary pocket flashlight as an example, then if you turn it on, it will seem to mean a logical one, and if you turn it off, it will mean a logical zero.

In digital electronic circuits, logical units of 1 and 0 are taken to be a certain level of electrical voltage in volts. So, for example, a logical one will mean 4.5 volts, and a logical zero will mean 0.5 volts. Naturally, for each type of digital microcircuit, the voltage values ​​of logical zero and one are different.

Any letter of the alphabet, as in the example with the Morse code described above, in digital form, will consist of a certain number of zeros and ones, arranged in a certain sequence, which in turn are included in packets of logical pulses. So, for example, the letter A will be one packet of impulses, and the letter B will be another packet, but in the letter B the sequence of zeros and ones will be different than in the letter A (that is, a different combination of the arrangement of zeros and ones).

IN digital code, you can encode almost any type of transmitted electrical signal (including analog), and it doesn’t matter whether it is a picture, video signal, audio signal, or text information, and you can transmit these types of signals almost simultaneously (in a single digital stream).

3. Analog devices

With the advent of electricity, people had the opportunity to use equipment powered by current. Every day more and more new devices appeared, science developed, technology improved. Back then, all inventions were considered analog. The word “analog” meant that the device works by analogy with something. To make it clearer, let's consider a measuring device. Let's say you need to build a graph of measurements; the measurement data themselves are known. The instrument will first derive an equation from the known data that describes the behavior of the graph, and then attempt to construct the graph. It works by analogy with an equation and strictly obeys its laws. And how accurately the equation describes the graph is not important to the device. Thus, analog electronic devices are devices for amplifying and processing analog electrical signals, made on the basis of electronic devices. There are two large groups, by which analog electronic devices can be classified:

· Amplifiers are devices that, using the energy of a power source, form a new signal that is in shape a more or less exact copy of the given one, but exceeds it in current, voltage or power.

· Amplifier-based devices are mainly converters of electrical signals and resistances.

Electrical signal converters ( active devices analog signal processing) - are performed on the basis of amplifiers, either through the direct use of the latter with special feedback circuits, or through some modification of them. These include devices for summing, subtracting, logarithming, antilogarithming, filtering, detecting, multiplying, dividing, comparing, etc. Resistance converters are made on the basis of amplifiers with feedback. They can transform the magnitude, type, and nature of resistance. They are used in some signal processing devices. A special class consists of all kinds of generators and related devices.

4. Digital devices

Digital are measuring instruments that automatically generate discrete signals of measurement information and give readings in digital form. Under discreteunderstand signals whose values ​​are expressed by the number N of pulses. A system of rules for representing information using discrete signals is called a code. Discrete signals, unlike continuous ones, have only a finite number of values, determined by the selected code.

The main and mandatory functional units of electronic digital measuring instruments are analog-to-digital converters, in which the measured analogue, i.e. continuous in time, the physical quantity X is automatically converted into an equivalent digital code, as well as digital reading devices in which the received code signals N are converted to numeric characters decimal system notations convenient for visual perception. The digital form of presentation of the measurement result, compared to the analogue one, speeds up the reading and significantly reduces the likelihood of subjective errors. Since most digital measuring instruments contain preliminary analog converters designed to change the scale of the measured input value x or convert it to another value Y = f(x), more convenient for the selected encoding method, then general case The block diagram of the device is presented in the form of Fig.

Block diagram of a digital measuring device

Modern digital instruments contain analog-to-digital converters capable of producing hundreds or more conversions per second, which makes it possible to record rapidly occurring physical processes and easily interface research objects with a computer. Digital devices are a new stage in the evolution of technology that works using digital data.

For clarity, let's consider the same case - you need to build a graph based on given measurements. The device will not create an equation; it will divide the graph into small pieces, and based on the known data, calculate the coordinates for each piece. Then the device will plot each piece according to the obtained coordinates, and due to the fact that there are a huge number of such pieces, they will represent a continuous graph. This is how digital technology works.

5. The main advantages of digital instruments over analogue ones

A digital signal, due to its electrical properties (as in the example with a tone signal), has a greater information transmission capacity than an analog signal. Also, a digital signal can be transmitted over a greater distance than an analogue one, without reducing the quality of the transmitted signal. For example, a continuous audio signal transmitted as a sequence of 1s and 0s can be reconstructed without error, provided that the transmission noise was not sufficient to prevent identification of the 1s and 0s. An hour of music can be stored on a CD using about 6 billion binary digits. This is especially true in recent years, taking into account the enormous growth in transmitted information (increase in the number of television and radio channels, increase in the number of telephone subscribers, increase in the number of Internet users and the speed of Internet lines).

Storing information in digital systems is easier than in analogue ones. The noise immunity of digital systems allows data to be stored and retrieved without corruption. In an analog system, aging and wear can degrade the recorded information. In digital, as long as the overall interference does not exceed a certain level, information can be restored absolutely accurately.

Digital systems with computer controlled can be controlled using software, adding new features without replacing hardware. Often this can be done without the involvement of the manufacturer by simply updating the software product. This feature allows you to quickly adapt to changing requirements. In addition, it is possible to use complex algorithms that are impossible in analogue systems or feasible, but only at very high costs.

When transmitting a digital television signal, the viewer will no longer see such a defect as “the image is snowy”, as was the case with an analog signal with poor reception. In the digital transmission of TV channels, the picture quality can only be good, or there will be no picture at all if the reception is poor (that is, either yes or no).

Regarding digital transmission telephone conversations, then here, with good quality Both a whisper and a scream, both low tones and high tones can be transmitted, and it doesn’t matter at what distance the telephone subscribers are located.

Digital technology has always been superior to analog technology in accuracy. For example, let's compare analog and digital voice recorders. If you need to record voice information, a digital device will cope with the task better than an analog one. This will be noticeable in the recording quality. The fact is that an analog recorder does not reproduce information so accurately; noise will be mixed into the recording, while a digital recorder will filter out unnecessary noise, and accordingly the sound will be more believable.

Digital technology is smaller. The devices are built on microcircuits capable of performing addition and subtraction operations on numbers, hence their small size. Unlike analogue devices, data from modern devices can be quickly processed by computers. Of course, analogue data can also be placed in a computer, but it will first need to translate them into “its” digital language.

Digital technology is more economical and lasts longer. Microcircuits consume less energy and can work properly for a long time, while mechanical equipment will quickly fail.

Digital devices also boast:

· Small error. The accuracy of analog instruments is limited by the errors of the measuring transducers, the measuring mechanism itself, scale errors, etc.

· High performance (number of measurements per unit time);
When measuring time-varying quantities, performance plays an important role. If indicating priors do not require high speed, since the capabilities of the operator working with them are limited, then, on the contrary, the requirement of speed becomes important when processing information using computers, to which digital devices are often connected.
· The absence of a subjective error in readings of the measurement result - subjective errors associated with the characteristics of human vision, due to parallax, due to the resolution of the eye.

6. Digital filter

Digital filter - in electronics, any filter that processes a digital signal in order to highlight and/or suppress certain frequencies of this signal. Unlike a digital filter, an analog filter deals with an analog signal, its properties non-discrete, accordingly, the transfer function depends on the internal properties of its constituent elements.

The advantages of digital filters over analog ones are:

· High accuracy (the accuracy of analog filters is limited by element tolerances).

· Stability (unlike an analog filter, the transfer function does not depend on the drift of the characteristics of the elements).

· Flexibility of configuration, ease of change.

· Compactness - an analog filter at a very low frequency (fractions of a hertz, for example) would require extremely bulky capacitors or inductors.

But there are also disadvantages:

· Difficulty working with high frequency signals. The frequency band is limited by the Nyquist frequency, which is equal to half the signal sampling frequency. Therefore, analog filters are used for high-frequency signals, or, if high frequencies there is no useful signal, first they suppress high-frequency components using an analog filter, then process the signal with a digital filter.

· Difficulty of working in real time - calculations must be completed within the sampling period.

· High accuracy and high speed signal processing require not only powerful processor, but also additional, possibly expensive, Hardware in the form of high-precision and fast analog-to-digital converters.

7. Analog-to-digital converter

Typically, an analog-to-digital converter is electronic device, converting voltage into binary digital code. However, some non-electronic devices with a digital output should also be classified as this type, for example some types of angle-to-code converters. The simplest single-bit binary converter is a comparator.

ADC Resolution- minimal change in value analog signal, which can be converted by this device - is associated with its bit capacity. In the case of a single measurement without taking into account noise, the resolution is directly determined by the bit capacity of the converter.

ADC capacitycharacterizes the number of discrete values ​​that the converter can produce at the output. In binary devices it is measured in bits, in ternary devices it is measured in trits. For example, a binary 8-bit converter is capable of producing 256 discrete values ​​(0...255), since . The 8-bit ternary is capable of producing 6561 discrete values, since .

Conversion frequencyusually expressed in counts per second. Modern ADCs can have a capacity of up to 24 bits and a conversion speed of up to a billion operations per second (of course, not simultaneously). The higher the speed and bit capacity, the more difficult it is to obtain the required characteristics, the more expensive and complex the converter. Conversion speed and bit depth are related to each other in a certain way, and we can increase the effective conversion bit depth by sacrificing speed.

Quantization noise- errors that occur when digitizing an analog signal. Depending on the type of analog-to-digital conversion, they can arise due to rounding (to a certain digit) of the signal or truncation (discarding the low-order digits) of the signal.

To ensure sampling of a 100 kHz sinusoidal signal with an error of 1%, the ADC conversion time must be 25 ns. At the same time, using such a high-speed ADC, it is fundamentally possible to sample signals with a spectrum width of about 20 MHz. Thus, sampling using the device itself leads to a noticeable discrepancy between the requirements between the ADC speed and the sampling period. This discrepancy can reach 2...3 orders of magnitude and greatly increases the cost and complexity of the sampling process, since even for narrowband signals it requires fairly high-speed converters. For a relatively wide class of rapidly changing signals, this problem is solved by using sample-and-hold devices that have a short aperture time.

8. Digital and analogue copying

Since the late 90s, the market for large-format copiers and engineering systems There is a clear trend of transition from analogue to digital technology. Nowadays, most manufacturers have modified their product line. Many of them have completely abandoned the production of analogue copiers.

The trend towards digital technology is completely understandable. Firstly, many enterprises that want to keep up with the times and be competitive solve the problem of transferring document flow to electronic view. Secondly, the requirements for the quality of documents are increasing, which determines the image of the enterprise in the eyes of partners and customers.

In this regard, multifunctional digital technology has significant advantages over analogue technology, due, first of all, to the very principles of digital and analogue copying.

Advantages:

· Possibility of connecting to a computer

· Digital technology can not only copy documents, but also print files from a computer, as well as scan originals and convert them into electronic form, for example, for saving in an electronic archive. Analog devices can only copy.

· Copy quality

· Digital technology makes it possible to obtain copies of more High Quality, since the file scanned into the machine’s memory can be digitally processed. The most useful use of this feature is to clear the background when copying blueprints. In addition, digital cameras support photo mode and render shades of gray and halftones much better. When copying color images, digital machines can differentiate between different colors by printing them in different shades of gray.

· In addition to this, digital technology does not use optics that transmit light reflected from the original to the photodrum. This optics for analog devices requires regular maintenance as it collects dust, which also affects the quality of the prints.

· Wide functionality

· Digital processing of the original allows not only to improve the quality of copies, but also to transform the original, for example, scaling, applying inversion, negative, etc.

· Reliability

· The higher reliability of digital technology is associated not only with the absence of optics and a backlight lamp, which needs to be changed regularly, but also with a different method of replication. When making a print run on an analogue machine, the original must not only be pulled in the scanning direction, but also returned to its original position before the next copy. The digital machine feeds the original once, memorizes it and then produces copies, printing copies from memory.

9. Digital and analogue music equipment

For a long time now, in our time of digital technology, we have stopped thinking about how more convenient digital hardware resources are compared to analog ones. In principle, when the transition from analogue to digital equipment was just beginning, there was a lot of debate on the topic of ease of use, technical advantages and, conversely, disadvantages of digital over analog. But now from time to time this question still arises in different situations, both in various recording studios and in clubs. What are the advantages of digital equipment over analogue and how is digital inferior to older designs?

First, let’s briefly talk about the principles by which audio digitization is based.

To convert analog sound to digital, there are analog-to-digital converters; it is these devices that are capable of converting a continuous analog signal into a sequence of individual numbers, that is, making it discrete. The conversion occurs as follows: a digital device measures the amplitude of the analog signal many times per second and outputs the results of these measurements directly in the form of numbers. At the same time, the measurement result is not an exact analogue of a continuous electrical signal. The completeness of the match depends on the number of measurements and their accuracy. The frequency at which measurements are made is called the sampling rate, and the precision of amplitude measurements indicates the number of bits used to indicate the measurement result. This parameter is the bit depth.

So, converting an analog signal to a digital signal consists of two stages: discreditby time and quantization(leveling) in amplitude. Discrediting by time means that the signal is represented by a series of its readings (samples), taken at equal intervals of time. For example, when we say that the sample rate (more commonly called the sampling rate) is 44.1 kHz, this means that the signal is sampled 44,100 times per second. As a rule, the main question at the first stage of converting an analog signal into a digital one (digitization) is choosing the frequency of the analog signal, since the quality of the conversion result directly depends on this. It is believed that the range of frequencies that a person hears is from 20 to 20,000 Hz, and in order for an analog signal to be accurately reconstructed from its samples, the frequency of discredit must be at least twice the maximum audio frequency. Thus, if a real analog signal, which will subsequently be converted to digital form, contains frequency components from 0 kHz to 20 kHz, then the sampling frequency of such a signal must be no less than 40 kHz. During the process of discrediting, the frequency spectrum of analog sound undergoes very significant changes. Once discredited, the relatively low-frequency original analog signal is a sequential time series of very narrow pulses of varying amplitudes and with a very broad spectrum of up to several megahertz. Therefore, the spectrum of the discredited signal is much wider than the spectrum of the original analog signal. Hence the conclusion: the most appropriate digitization occurs on increased frequency discredited and with high bit depth.

The operating principles of analog equipment are based on the continuity of the signal in the electrical circuit. The reason for the transition of production technologies from analogue to digital was the need, first of all, to improve sound quality, storage, and automation of the work process. But at the same time, due to the compression of the original signal after the digitization process, the CD is inferior in overall sound quality to vinyl, since the frequency range of the original signal during analog recording undergoes virtually no changes (as for noise reduction, this also depends on the needles on the players) . That's why professionals prefer the sound of vinyl to CDs.

10. Disadvantages of digital devices

I would like to devote a few more words to the disadvantages of digital technology, which can be very important in mass production.

In some cases digital circuits use more power than analog to perform the same task, generating more heat, which increases circuit complexity, for example by adding a cooler. This may limit their use in battery-powered portable devices.

For example, Cell Phones often use a low-power analog interface to amplify and tune radio signals from a base station. However, the base station can use a power-hungry but highly flexible software-defined radio system. Such base stations can be easily reprogrammed to process signals used in new cellular communication standards.

Digital circuits are sometimes more expensive than analog ones.

It is also possible to lose information when converting an analog signal to a digital one. Mathematically, this phenomenon can be described as a rounding error.

In some systems, the loss or corruption of one piece of digital data can completely change the meaning of large blocks of data.

Bibliography

analog digital signal device

1. Horowitz P., Hill W. The Art of Circuit Design. In 3 volumes: T. 2. Trans. from English - 4th ed., revised. and additional - M.: Mir, 1993. - 371 p.

Hanzel G.E. Handbook for calculating filters. USA, 1969. / Transl. from English, ed. A.E. Znamensky. M.: Sov. radio, 1974. - 288 p.

. "Digital signal processing". L.M. Goldenberg, B.D. Matyushkin - M.: Radio and communication, 1985

Biryukov S.A. Digital devices on MOS integrated circuits / Biryukov S.A.-M.: Radio and communications, 2007.-129 pp.: ill. - (Mass Radio Library; Issue 1132).

Gorbachev G.N. Chaplygin E.E. Industrial electronics / Ed. prof. V.A. Labuntsova. - M.: Energoatomizdat, 1988.

Shkritek P. Reference guide to audio circuitry: Transl. from German-M. Mir, 1991. - 446 pp.: ill.

Shilo V.L. Popular digital microcircuits: Directory / Shilo V.L.-M.: Metallurgy, 2008.-349 p. - (Mass Radio Library; Issue 1111).

Goldenberg L.M. Pulse and digital devices: Textbook for universities / Goldenberg L.M.-M.: Communication, 2009.-495 p.: ill..-Bibliography: p. 494-495.

Bukreev I.N. Microelectronic circuits of digital devices / Bukreev I.N., Mansurov B.M., Goryachev V.I. - 2nd ed., revised. and additional..-M.: Sov. radio, 2008.-368 p.

Greetings, dear friends, colleagues and partners!

“Which strain gauges are better - digital or analog? And for whom are they better?

I've been hearing these questions more and more lately. And the answers to them more and more often have opposite meanings - someone proves that digital sensors- this is a panacea for all problems in the operation of scales, others, on the contrary, are their source.

In the ranks of the disputants, several main interested groups of specialists can be identified, providing various stages life cycle weighing systems:

• developers, manufacturers and sellers of sensors and other components of scales;
• developers, manufacturers and sellers of scales themselves and weighing systems in general;
• employees of metrology centers;
• specialists from repair organizations;
• consumers-buyers of scales.

Daily contact with all of the listed groups of specialists, as well as the business model of the enterprise I manage, which simultaneously carries out commercial, innovative, design, production and operational activities, forces me to constantly speak out and defend the interests of one or another group.

In this article I will try to describe the main features of the use of analog and digital sensors with the minimum possible number of technical terms and complicated technical information.

But before we start describing all the pros and cons, let's first understand in a simplified form the principle of operation of scales with analog and digital strain gauges.

Typically, when using analog sensors The following connection diagram is used (a simplified version using the example of automobile or carriage scales):

Diagram 1: Connecting analog load cells in truck scales.

Information from analog strain gauges goes through the cable to the connection terminal box. As a rule, precision resistors are installed in the box to equalize the sensitivities of each sensor and their analog summation. After this, the total signal enters the weight indicator, where the signal is digitized using an analog-to-digital converter (ADC). The same indicator has a scale calibration program that assigns a digital code to values ​​in mass units (kg, grams, tons, etc.)

A simplified structure of a weighing system using digital sensors is presented below:

Diagram 2: Connecting digital load cells in truck scales.

When using digital strain gauges, measurement occurs in exactly the same way as when using analog ones. The only difference is that digitization occurs not in the weight indicator, but in each sensor separately, and then the digital code is transmitted to the connection box and to the weight indicator or computer. If a weight indicator is not used, then the system is calibrated and the results are visualized using special software on a computer.

Now let's take a step-by-step look at the main differences between the use of digital and analog strain gauges and, as a consequence, their advantages and disadvantages.

1. Method of transmitting data from the strain gauge to the system (difference between a digital signal and an analog signal).

The difference between the methods of transmitting signals by analog and digital strain gauges to the weighing system is as follows.

Here, of course, digital sensors win over analog ones. A digital signal can be transmitted over 1000 - 1200 meters, without significant deterioration in quality, unlike analogue: up to 200 meters. Here you just need to decide whether you need such a distance from the sensors to the weighing terminal?!

3. When replacing digital load cells, calibration and verification of the scales is not required. Is it so?

Yes and no! That is, theoretically, you can change the digital sensor, and knowing certain calibration coefficients (information about the conversion characteristics from the accompanying documentation for the sensor) register them in the weighing device. This is enough to restore the functionality of the scales. The scales will work, aiming for the middle class of accuracy. But without calibrating the scales with a reference weight, it is illegal to work on such scales (according to existing technical regulations and GOSTs). All numbers of sensors installed in automobile scales are recorded in the passport, in which the verifier puts his signature and seal, indicating that the scales correspond to the average accuracy class and are ready for use.

And when replacing any of the sensors, it is necessary to invite a metrologist (verifier) ​​with a standard load and re-calibrate the scales. And after that, make changes to the passport for the scales, writing down the new number of the installed sensor.

4. Which strain gauges are more accurate, digital or analog?

This is the wrong question to begin with. The accuracy of weight sensors, as well as scales in general, is determined by the limits of permissible absolute measurement errors expressed in units of mass through e - the value of the verification division. And it does not depend on whether the sensor is analog or digital.

The accuracy of sensors is expressed by Accuracy Class (according to OIML these are C2, C3, C4, C5), and is determined by the level of development, technological and metrological capabilities of the enterprise - the manufacturer of sensors.

That is, the accuracy of digital and analog sensors is the same, provided that these sensors are of the same accuracy class.

5. In what systems can you see the readings of each sensor separately? And why is this?

As I wrote above, information from analog strain gauges is digitized only after it is summed up in the connection box. That is, we cannot obtain digital data from each sensor. We see the digital code, and subsequently the weight, from all sensors, and not from each one separately. In digital sensors, the signal is digitized immediately in the strain gauge, that is, we receive data from each sensor.

Why is this necessary? If it is necessary to compare or analyze weight values ​​from each strain gauge, for example, in carriage or truck scales to determine the center of gravity or even loading of the carriage, analogue sensors without additional devices are not suitable for us.

6. Interchangeability of strain gauges different manufacturers and working with different weight indicators.

There are currently no interchangeable digital load cells from different manufacturers. Regarding the interchangeability of sensors from different manufacturers, analog sensors are preferable.

Digital load cell and different manufacturers have their own data exchange protocols, therefore, when replacing, it is necessary to replace the sensor only with the same one. And these sensors only work with “OWN” proprietary digital indicator or software.

In analog systems, everything is much more unified. Not only are sensors from almost all well-known global manufacturers interchangeable, but a weighing device can be used with them from any manufacturer, as long as it meets the technical specifications.

7. Which strain gauges are more reliable: analogue or digital?

We all know that the fewer elements in a system, the less likely it is to fail. The presence of an additional electronic board in the design of a digital sensor potentially degrades its reliability.

However, the reliability of electronic components of embedded analog-to-digital and processor elements, compared with the operational reliability of elastic elements, strain gauge structures and electronic boards settings of analog sensors are significantly higher.

Therefore, it must be recognized that the reliability of analog and digital sensors is “roughly” equal, despite the fact that digital sensors use more electronic components.

8. Price.

As a rule, all companies claim that the price of digital sensors is higher than analogue ones. And they are all almost right. More precisely, a little wrong. If you compare the cost of an analog sensor from a German or American manufacturer with a digital sensor from a Chinese manufacturer, then there is a high probability that a digital sensor from a Chinese manufacturer is cheaper. And this absolutely does not mean that he is worse. This is influenced by other factors, which are described in.

Well, if you compare the cost of analog and digital sensors from the same manufacturer, then of course the digital one will be more expensive.

At this point I want to combine several advantages of digital sensors, such as:

9. Ease of setting up scales, diagnosing breakdowns, and servicing.

Let's take turns. Let's start with the fact that the installation of strain gauges in scales occurs in the same way, since the overall dimensions of the same model are the same. It is the setting of the scales themselves that differs.

How does this happen? The first thing to do after installing all the sensors is the so-called “corner alignment”. As I wrote earlier, in analog sensors this happens using resistors in the connecting summing box. By changing the resistance of one of the resistors, we bring the system to the same data. (this is done so that wherever the load is on the platform, the indicators are the same). In digital sensors, such adjustment is done using special coefficients that the adjuster enters into the memory of the weight indicator. That's all. This is exactly the difference.

As for diagnosing scales. With digital sensors this is very simple. The weighing device itself will “show” which sensor has failed, since it constantly polls each sensor for functionality (so-called “self-diagnosis”).

If an analog sensor fails, it will be necessary to determine the failure by disconnecting one sensor at a time from the junction box. Or disable everything and diagnose them one by one. But, as a rule, even this complexity of the procedure will not take more than half an hour from a specialist.

Servicing or replacing a broken sensor is the same. The difference is that when using an analog sensor, it will be necessary to “adjust” the system again using resistors, as I wrote above. In digital – re-enter the coefficient. And then it will be necessary to verify the scales, regardless of the type of sensor.

Also, many argue that if one digital sensor fails, the car scales will continue to work. Of course there will be, but not one self-respecting manufacturer or metrologist will take the responsibility to claim that the system works without additional error. This error depends, first of all, on the location of the load on the weighing platform. And if most of the weight of this load falls on an inoperative sensor, the error can increase significantly.

Let us now briefly display the differences between analog and digital strain gauges in a table.

Criterion	Analog strain gauges	Digital strain gauges
Noise immunity	Good up to 200m	Good up to 1200 meters
Distance from scale to device		Up to 1200 meters
Calibrating the scale when replacing the sensor	Required	Required
Accuracy		Determined by accuracy class (According to OIML C2, C3, C4, C5...)
The ability to “see weight” from each sensor	No possibility	There is a possibility
Interchangeability	Load cells from different manufacturers are interchangeable and work with different weight indicators is possible.	The sensors are interchangeable only with the same ones. Work with weighing instruments only from the same manufacturer.
Reliability	About the same, but has a simpler structure	About the same, but has a more complex structure
	Below, when comparing the same manufacturer	Above, when comparing the same manufacturer
Ease of setting up scales, diagnosing breakdowns, and servicing	Less convenient	More convenient

Result:

Of course, from the point of view of ease of diagnosis, configuration and maintenance, digital sensors are better and preferable to use. But it is better and more preferable for the manufacturer and repair and maintenance organizations.

For consumers (buyers) electronic scales There are no obvious advantages when using digital sensors in scales compared to analog ones.

Main advantage analog sensors:

Price advantage. When creating scales and replacing analog sensors in case of breakdowns (lightning, overload...) their use is made more profitable.

Clear two advantages digital strain gauges:

• determination of not only the total weight of the weighed goods, but also its distribution(difference in loading of bogies of a railway car, determination of the position of the displacement of the center of mass, etc.). When building such weighing systems using digital sensors, it is possible to know information about the current loads on each sensor separately.
• transmission of information from sensors to electronic processing equipment over a distance of up to 1200 m. This is due to the fact that digital channels information transmission from the point of view of maintaining the accuracy of the signal properties is more effective.

And in conclusion, it is necessary to consider hybrid analog-digital systems, which, when using analog sensors, allow receiving information flows from each individual sensor and, if necessary, organizing digital channels for transmitting information in scales. Structural diagrams transformations in such systems can be represented as follows:

Scheme 3: Connecting analog strain gauges via an 8-channel ADC.

Scheme 4: Connecting analog strain gauges via an 8-channel ADC built into the weight indicator.

The implementation of such structural transformations is possible using multi-channel analog-to-digital converters (ADCs). Structurally, they are not combined with sensors and can be located either in a digital weighing indicator, with information from each sensor to the indicator being transmitted in analog form, or directly next to the sensors (for example, under the weight-receiving platform), with information being transmitted to the weighing system in digital form .

In this way, you can get the benefits of systems using both digital strain gauges and analogue ones.

I hope that my reasoning will complement your ideas about modern schemes for constructing weighing strain gauge systems and will be useful to you in practical activities!

Many other interesting articles You can look at strain gauges and their applications on our website in the ARTICLES section.

CEO group of companies "World of Libra" (Ukraine),

General Director of ZEMIK CIS LLC (Russia),