RU2333505C1 - Differential voltmeter-controlled wide-range calibrator - Google Patents

Abstract

FIELD: metrology.

SUBSTANCE: invention relates to metrology and can be used in designing the high-accuracy voltage (current) reproduction and measurement in a wide range. The proposed differential-voltmeter-controlled wide-range calibrator incorporates an amplifier with a scaling divider in the feedback circuit connected to the calibrator terminal, a reference voltage source and reference voltage digital-analog converter (DAC) with its output connected to the aforesaid amplifier input and DAC input, and with its second input is connected, via the differential voltmeter input scaling circuit, to the meter input terminal. Note that DAC is connected so as to allow writing its digital code into the DAC control circuit, the calibrator output being connected, via switch contacts, to the control differential voltmeter.

EFFECT: simplification, higher-accuracy and deeper self-diagnostics.

3 cl, 6 dwg

Description

The invention relates to measuring technique and can be used in the design of high-precision reproduction and measurement of voltage (current) in a wide range. In accordance with traditionally accepted practice (and primarily foreign), these tasks are solved independently - with a measuring device (multimeter-multimeter) or stimulating (calibrator). According to the current domestic standard (classifier), these devices are represented by group "B" (voltmeters and multimeters: B2-39, B3-71, B7-64, etc.) and group "H" (calibrators: H4-6, H4- 7, H5-4, etc.). The world leader (and practically a monopolist) in the field of development, production and sales of multimeters and calibrators is the company "FLUKE", USA. This company has today in production entire lines of the world's best calibrators and multimeters [1].

The calibrator is a multi-valued measure of voltage (amperage). A wide network of voltages (currents) is formed from a voltage of a single measure - a source of a reference (reference) voltage, by digital-to-analog conversion of the latter.

The well-known high-precision voltage calibrator is described in [2]. It contains a reference voltage source Vet, from which a voltage grid K 100 V and 1000 V) {fg.2b in [2]}. The gain of the power amplifier is determined by the ratio of the resistances of the resistors in its feedback circuit (R2 / R1). Thus, the output voltage of the calibrator is determined by the expression: U _OUT = K · (R2 / R1) · Vet. Figure 5 in [2] shows a simplified diagram of the output amplifier of the calibrator, and on pages 31 and 32 are measures that provide high-precision voltage reproduction in the high-voltage region of the range.

Requirements for the amplifier (low zero drift and high gain of 10), requirements for feedback resistors: improving the time and temperature characteristics of resistors ("compared with commercially available"), through the use of special manufacturing technology, subsequent selection of resistors with agreed characteristics (according to the DRM method patented by the company), active temperature control; finally, measures to reduce the effect of self-heating of resistors due to power dissipation when the voltage across them changes from zero to 1000 V. The latter are achieved by reducing the power factor (“PC” - heating the resistor for each watt of power). To this end, the resistor forming the limit of 1000 V is assembled from a chain consisting of 10 series-connected resistors located in a large active thermostat.

The fight against self-heating of resistors is the most complex and resource-intensive, since this component of the error is not eliminated either by auto-calibration or by temperature control. The free actions of the operator may require the installation of any of the possible voltages, at any (and at any) time. For example, set 1000 V (heating up the resistor) and then 50 V (cooling).

Much attention is paid to this issue when designing the high voltage limits of the calibrator. As a rule, you have to make a compromise decision. This error component can be minimized by significantly increasing the resistance of the divider in the feedback circuit, but the errors increase due to the finite input resistance of the amplifier (and the input capacitance for the AC voltage calibrator), insulation resistance of the mounting material (substrate) and switching elements (relays, switches). With a decrease in the resistance of resistors, self-heating increases, and the influence of transition resistance of contact groups of switching elements increases. In [2], it is formulated as follows: “Additional measures are also taken to reduce the influence of“ second-order factors ”:“ transition resistance of switching elements, insulation resistance (leakage currents) ”([2] p. 32).

We draw attention to the fact that all these measures are applied in a device that implements auto-calibration (hardware is provided by an analog-to-digital converter (ADC) controlled by a special program). “Normally, internal calibration is done daily, but it can be done additionally in cases of large changes in ambient temperature.” But auto-calibration cannot eliminate the changes that occur in the intervals between its next inclusions. It does not eliminate the error caused by self-heating of resistors in the feedback circuit of the output amplifier (“range resistors”) when the output voltage increases (decreases); error from the effects of the load. In the calibrator under consideration, all these shortcomings are eliminated not by software but by hardware resources (temperature control, selection and coordination of resistor characteristics, increase in gain, technological methods [2]). The fact is that the principles of autocalibration are in good agreement with the discrete operation of a digital voltmeter (ADC), where it is possible to enable autocorrection cycles (and even one of the cycle steps) between measurements (for example, through 1, 10, 100 ... measurements), and almost unacceptable in a "clean" calibrator. This is due to the fact that a continuous (analog) signal is generated at the calibrator output, the state of which is monitored by a closed auto-regulation system, which cannot be interrupted. For this reason, the information necessary for auto-calibration procedures can be obtained only by including a calibrator-meter (voltmeter, ADC) in the circuit, which was done in [2]. But the auto-calibration procedure requires interruption of the voltage reproduction process. The practical implementation of continuous auto-correction of the calibrator output is possible only when a voltmeter (ADC) is included in its circuit, which controls the output of the calibrator and corrects, if necessary, its output voltage. The proposed solution is most effectively implemented in the design of differential voltmeters [3, 4], since these devices contain everything necessary for the implementation of the proposed solution: a reference voltage source, a digital-to-analog converter, which provides the formation of a multi-bit voltage grid, which balances the input (measured) voltage. The difference between the input and the compensating voltage is measured with a microvoltmeter. The latter is a sensitive ADC. Turning to a unified (generally accepted) terminology, we note that the source of exemplary voltage with a multi-bit voltage divider is a DAC with an internal source of reference voltage. In accordance with this, the differential voltage measurement circuit takes the form of figure 1.

The differential voltmeter (LW) in figure 1 works as follows:

- at the first stage, when the DAC is zeroed (Ucap = 0), the input voltage Uin (for example, 1 V) is measured by the ADC (“rough” measurement) with its minimum sensitivity. The measured voltage value (for example, 0.999 V) from the ADC is "overwritten" in the DAC (in code format). As a result, the voltage (999 mV) equal to the input with an error (-1 mV) of the ADC is set at its output.

- at the second stage, with increased sensitivity of the ADC, the difference Uin-Ucap is measured (1 V - 999 mV = 1 mV, taking into account the error of the ADC at the second stage, 0.999 mV). The DV reading is based on the state of the DAC and ADC (i.e., 0.999999 V).

To measure voltages in a wider range, the single-limit DW (Fig. 1) is supplemented by an input divider that extends the range of measured voltages to values that exceed Ucap by several orders of magnitude. Thus, a simplified diagram of a multi-limit DW takes the form of FIG. 2.

The input device of a multi-limit voltmeter (divider or divider with an input amplifier) carries out the normalization of the input signal (bringing to a level acceptable for the normal operation of the subsequent circuit).

If the DAC (with an internal reference voltage source) is supplemented with a voltage (power) amplifier, then the voltage can be reproduced, which opens up the possibility of creating devices that provide both measurement and reproduction of voltages (voltmeters-calibrators).

The closest in technical essence to this invention is a differential voltmeter calibrator B 1-18. Its full name (according to the old classifier) is “A device for checking voltmeters and calibrators V 1-18” [4], which provides measurement of DC voltage up to 1000 V and voltage reproduction up to 12 V for stand-alone use and up to 1000 V in conjunction with V9 converter -12 [5]. (The author is the chief designer of the development of the complex B1-18, B9-12).

Figure 3 shows a simplified diagram of the device B 1-18 (blocks 1-6) and the transducer B9-12 (blocks 7-12). The operation of the device (B 1-18) in the measurement mode does not differ from that described above. The input voltage (clamp 5) through the input device is fed to the input of the ADC 1. In block 4, containing the input divider (with transmission coefficients 1:10 and 1: 100), the input signal is normalized (converting the input signal into a standard one in terms of type and range of values ) At the other input of the ADC 1, a compensating voltage is supplied from the output of the digital-to-analog converter 2 of the voltage Uop (reference voltage source 3).

To implement the function of a calibrator with output voltages up to 1000 V, a complex of device B 1-18 and voltage converter B9-12 is aggregated, which performs large-scale conversion (with transmission coefficients 1, 10 and 100) of the voltage from the output of DAC 2, for which it contains there is a high-voltage amplifier 9, covered by a negative feedback loop through a highly stable divider 10 with a ratio mr / r (m = 1, 10, 100). The output voltage is removed from terminal 7.

To implement the current calibrator mode, a voltage-current (U / I) converter 11 is included in B9-12, which converts the voltage of the DAC 2 into current (up to 110 mA) at the output terminal 12.

All the problems noted above for the high-voltage voltage calibrator are inherent in this product:

- high sensitivity and a large gain of the calibrator amplifier, since the auto-regulation system based on it should ensure maximum stability of the set voltage level in conditions of significant fluctuations in the supply voltage and load;

- high metrological characteristics of the divider in the amplifier feedback loop over the entire range of set voltages, with changes in ambient temperature and time.

The aim of the invention is to simplify, improve the accuracy and depth of self-diagnosis.

This goal is achieved in that in a wide-range calibrator-differential voltmeter containing a calibrator amplifier connected to the output terminal of the device with a scaling divider in the negative feedback circuit, a reference voltage source and a digital-to-analog converter for this voltage, connected by its output to the input of the calibrator amplifier and the analog input -digital conversion, the other input of which is connected to the input scaling device of a differential voltmeter to Khodnev terminal device introduced through the auxiliary circuit output autoregulation loop calibrator input differential voltmeter.

Figure 4 presents a diagram of this calibrator-voltmeter.

In the measurement mode, the input voltage (Ux) is supplied (from the input terminal "10") through the input device (divider 1 and input amplifier "2") to the ADC input 3. The transmission coefficient of the input device has a transfer coefficient R / nR, where n> 1 . When the DAC 4 is zeroed (Ucap = 0) and the ADC sensitivity is minimal, the input voltage is measured “last” roughly, according to which the DAC is set (the ADC digital code is “written” to the DAC control circuit). After that, the voltage difference Ux-Usap (or, taking into account the transfer coefficient “1 / n” of the input device, Ux / n-Usap), which is measured by the ADC, but already at maximum sensitivity, is affected by the ADC. Based on the position of the DAC and the ADC readings, a voltmeter reading is displayed.

In the voltage (calibrator) playback mode, the switch “8” closes, the voltage Ucap is applied to the input of the amplifier of the calibrator 7 with the transmission coefficient nr / r (divider resistor ratio “6”). As a result, the voltage Uк = Uсап · n (where “n” is usually 1, 10 or 100) is formed at the output of the calibrator amplifier, which is controlled by a voltmeter, the measurement limit of which is set in accordance with the calibrator limit set (10V, 100V or 1000V) and, at necessary, adjusted.

The auto-regulation mechanism is illustrated by an example.

At the output of the calibrator amplifier, a voltage of 1000 V is set. In accordance with the operation algorithm, the voltage Ucap = 10 V is set, the limits of the calibrator and voltmeter are 1000 V (i.e. n = 100). Due to the error of the high-voltage amplifier (-0, 1%), the output voltage is set to 999 V, i.e. at the input of the ADC, the voltage is 9, 99 V (at the other input, the voltage is Usap = 10 V). The voltage difference (-10 mV) is recorded by the ADC, which corrects the voltage (10 V) installed at the DAC output by +10 mV (i.e., it is set to 10.01 V), which, after amplification by a factor of 100, gives the calibrator amplifier circuit increase in output voltage by 1 V, i.e. the voltage at the output of the calibrator becomes (as a result of correction) equal to 1000 V. Thus, any change in voltage at the output of the calibrator caused by the inaccuracy of the divider “6” (for example, self-heating of the resistors of the divider), drift of the amplifier or the influence of the load is controlled by an accurate voltmeter, which determines whether it is necessary to add or reduce the voltage at the input of the calibrator amplifier in order to obtain the required voltage at its output. It is obvious that with such a control algorithm, the accuracy of maintaining the output voltage is determined by the accuracy of the voltmeter.

When using a low-quality element base in the calibrator amplifier (tenths of a percent error of 10 ^-3 ), the ADC must have a scale that records this error, which, with the high required accuracy (linearity) of the calibrator (10 ^-6 -10 ^-7 ), may require 4 - 5-decade ADC, since the difference between the exact voltage of the DAC and the inaccurate voltage of the calibrator (Ucap-Ucal) acts on its inputs. Indeed, the correction of the calibrator output requires a corresponding change in Ucap (+10 mV in the previous example), while the voltage becomes accurate at the calibrator output, and 10.01 V and 10 V are applied to the ADC inputs, i.e. difference of 10 mV, which must be measured with an accuracy of units of microvolts. Thus, for the operation of a differential voltmeter, there is no need to have a full-scale DAC scale. The scale can be reduced by the number of bits of the ADC. However, for the operation of the calibrator, a full-scale DAC scale is necessary, which can be implemented in two ways: by adding low-order DAC grids or by turning on an additional DAC (13) at the input of the calibrator amplifier (Fig. 5), which, summing up (with the corresponding scale “m”) with voltage the main DAC, provides the formation at the output of the voltage calibrator with the required resolution. This solution allows us to simplify the circuit of the main DAC by reducing its bit capacity: all precision calibrators use DACs with pulse-width modulation of the reference voltage (PWM-DAC), by which the entire voltage grid is formed by a digital-to-analog converter of high and low digits ([2] p.29 ; [4] p. 52). The fact is that pulses with an amplitude equal to the reference voltage (10-20 V) are formed in the PWM-DAC, which should be smoothed by a low-pass filter up to 10-20 μV. The pulse repetition rate is chosen to be more than 100 Hz, since a lower frequency can cause a very significant settling time during filtration and, as a result, a decrease in the speed of the device. But even with a pulse repetition rate of 100 Hz at the output of a seven-decade DAC, at its input, the clock frequency becomes 100 · 10 ⁷ Hz, which creates obvious difficulties in practical implementation. By splitting the PWM-DAC into two (with a capacity of 10 ⁴ ), the problem is solved. However, this is not required when constructing a PWM-DAC in accordance with FIG. 5. An additional DAC is implemented in the form of an integrated (resistive) high-speed circuit, the accuracy of which does not matter, since the error is excluded by the action of the proposed feedback.

When constructing the structure of FIG. 5, the aspects of “internal” programming and device protection in extreme situations are rationalized. In accordance with the control algorithm, when the operator sets the voltage at the output of the calibrator, the main PWM-DAC is transferred to the corresponding state (with 4-decade resolution), which does not change until the next installation. Missing bits are implemented by an additional DAC. Under the influence of the load, the voltage at the output of the calibrator may change, which will require appropriate correction of the output, which is implemented by a corresponding change in the state of the additional DAC. At the same time, the state of the main measurement circuit, with its inertial link in the form of a PWM-DAC, does not change (i.e., the time to recharge the filter is not lost), and therefore, the reaction rate to the disturbance increases. So, for example, when the output is short-circuited (where the response speed is important), the entire capacity of the high-speed additional DAC is very quickly “selected” and the calibrator shutdown (protection) program and user alerts (audio or visual signal) are activated. Thus, the problem of operational protection is solved even with a significant inertia of the measurement circuit with a differential voltmeter (the actual ADC measurement speed is less than a millisecond, and the PWM-DAC is hundreds of milliseconds).

The inclusion of a voltmeter in the control circuit of the output value of the calibrator can significantly reduce the requirements for the characteristics of the latter. The requirements of high temperature and long-term stability are transferred to the voltmeter, but their implementation is simplified due to the possibility of automatic calibration of the voltmeter before each subsequent "intervention" in the calibrator output correction system.

As noted above, the discrete nature of the operation of the voltmeter, in contrast to the calibrator, is in good agreement with the principles of auto-calibration, where it is possible to turn on auto-calibration cycles in the pauses between measurements. Moreover, there is no need to calibrate in full (zeros and scales of all limits), and calibrate only the set limit. And since immediately after the auto-calibration the voltmeter has the highest accuracy, there is no need to form the voltmeter nodes from components with high long-term and temperature stability (these should be only internal standards by which the auto-calibration is implemented).

The use of a voltmeter to control the calibrator (and not vice versa) has other justifications due to the specifics of its operation. In the voltmeter, all corrective actions can be implemented “virtually” (only in the form of the presented corrected digital display), and in the calibrator, such actions can appear only in the “natural format” (in the form of a corresponding change in the output signal). Another example. Using the same amplifier in the circuit (comparison) of the voltmeter and in the circuit (auto-regulation) of the calibrator provides significant "metrological advantages" first. The noise characteristics of the amplifier (limiting its sensitivity) in the voltmeter circuit can be reduced by digital signal processing methods (statistical averaging), which cannot be implemented in the calibrator auto-regulation circuit. And in terms of reducing the error in measuring high voltages (up to 1000 V) caused by self-heating of the input divider, the voltmeter's capabilities are wider than in the calibrator circuit. Firstly, this error itself, as a rule, is an order of magnitude lower due to the high resistance of the input divider of the 10 V MOhm voltmeter (a requirement of current standards), and secondly, there is always the possibility of prompt (split second) auto-calibration, in the pauses between measurements, " warmed up "divider in order to minimize the error from heating.

Analyzing the scheme of figure 4, it should be noted that the function of the calibrator required minimal hardware costs, and regardless of metrological characteristics, not the highest quality. It was not necessary to enter anything (only an additional feedback loop and a switch), but the additional auto-regulation loop effectively affects almost all the characteristics of the calibrator.

The theoretical basis for this was the method of increasing accuracy based on the “model inverse transformation” ([3] p. 57), since analog-to-digital and digital-to-analog conversion are typical representatives of the “direct” and “inverse” conversion.

The universality of this method allows us to solve the inverse problem: to realize an accurate measurement with an inaccurate voltmeter controlled by an accurate calibrator. Those. build measuring and generator-type devices on the basis of the highest achievements of the best of them, achieving optimal technical solutions.

The practical basis for the creation of the claimed device was the fact that there is no need for a high-precision voltmeter and a high-precision calibrator. Only one of them should be highly accurate, and the other (less accurate) is controlled or calibrated to a more accurate one, providing in this case the metrological characteristics of the latter. This simple idea turned out to be very fruitful, since it effectively affects the whole complex of indicators of the device. As a result, the implemented set of functions, with minimal redundancy, has the lowest cost by reducing the cost of development, manufacture and maintenance during operation (only a voltmeter is calibrated and calibrated, the calibrator is checked only for operability).

Indeed, such components as a reference voltage source, components of analog-to-digital and digital-to-analog conversion, precision resistors, microcomputers, a display with a keyboard, communication elements with external and internal objects, etc., are inevitably duplicated in a single voltmeter and calibrator. Any single voltmeter and calibrator (even of lower accuracy) have a large total cost, which increases the cost of their maintenance and periodic calibration (calibration), due to the need to purchase a wider range of calibration tools and the volume of calibration work (for precision instruments, these costs significant).

And finally, the presence of a voltmeter and a programmable source with a wide voltage grid inside the device opens up wide possibilities for “total” auto-calibration and diagnostics of the device, including metrological failures, since the proposed structure implements all the basic operations of the measurement process: reproduction, measurement, comparison, scaling, and static information processing (built-in microcomputer).

By feeding (for diagnostic purposes) each bit in series from the DAC and controlling the ADC, you can implement the most in-depth diagnostics of both the DAC and the ADC. Based on the high linearity of the DAC (with PWM), to carry out the auto-calibration of the ADC, resistive dividers.

With even greater effect, the proposed solution can be implemented in the design of AC voltage calibrators. The fact is that the AC voltage playback function is the most resource-intensive part of the multifunction calibrator. In this case, the main difficulty is the technical implementation of the AC to DC converter, since its characteristics determine the accuracy of AC voltage reproduction. It is thanks to the creation of such an integrated converter that FLUKE takes a leading position. The company itself manufactures this converter using a patented technology, guarded by prohibitions on its sale and transfer.

Figure 6 shows a simplified diagram of the proposed device wide-range calibrator constant and alternating voltage controlled by a differential voltmeter. In terms of reproduction of direct voltage (switches 23 and 24 in the initial state), the circuit does not differ from that shown in Fig. 4.

To implement the AC voltage measurement mode, the voltmeter circuit is supplemented by a converter 20 of the measured AC voltage to DC, and then the operation of the differential voltmeter does not differ from the above. To implement the ac voltage reproduction mode, the necessary hardware minimum is introduced into the circuit: an ac voltage reference source (sinusoidal voltage generator 22) and an alternating voltage DAC 21, which ensures the formation of a multi-bit grid of the output voltage, which is fed to the input of the high voltage voltage amplifier 7 and then to the socket 9 calibrator outputs.

The requirements for metrological characteristics of nodes 21 and 22 are reduced, and therefore the possibility of using serial four-quadrant (providing conversion of DC and AC voltages) integrated DACs opens up, which greatly simplifies the device. However, there are such “non-metrological”, but important characteristics of the AC voltage (current) signals, such as non-linear distortions and ripples, which are not processed by the proposed feedback loop, and therefore these characteristics should be initially generated in nodes 21 and 22.

» вольтметра («20» фиг.6). Однако, как это было показано выше, в схеме измерения возможности метрологического совершенствования шире за счет внедрения алгоритмических и программных решений. Кроме того, в схеме вольтметра может быть применена самая высокочувствительная, широкополосная и самая простая схема преобразователя средних значений ([3], стр.140), которая имеет самые существенные достоинства применительно к калибратору. А ее самый главный недостаток применительно к вольтметру - значительная погрешность при измерении несинусоидальных напряжений (с «искаженной» формой) не имеет существенного значения применительно к калибратору, так как калибратор, по определению, должен генерировать чистейшую синусоиду (коэффициент гармоник должен быть минимальным). Таким образом, предложенное решение позволяет реализовать высокие характеристики калибратора переменного напряжения. А решать проблему измерения действующих значений переменного напряжения с искаженной формой приходиться традиционными методами, дополнив схему вольтметра более сложным устройством - преобразователем действующих значений. И в этом случае предложенная структура позволяет извлечь определенные преимущества за счет реализации процедур автокалибровки преобразователя действующих значений сигналами с выхода калибратора (в этом случае «ведущим» будет калибратор, а «ведомым» - вольтметр действующих значений). Такая автокалибровка позволяет реализовать высокую долговременную и температурную стабильность преобразования действующих значений, даже в тех случаях, когда он таковой не отличается.Since a solution is proposed that allows the "metrological" load to be transferred to the voltmeter circuit. In this case, the entire metrological load is carried by the converter "

"Voltmeter (" 20 "Fig.6). However, as was shown above, in the scheme of measuring the possibility of metrological improvement is wider due to the implementation of algorithmic and software solutions. In addition, in the voltmeter circuit, the most highly sensitive, broadband, and simplest medium-value converter circuit ([3], p. 140) can be used, which has the most significant advantages with respect to the calibrator. And its main drawback in relation to a voltmeter is the significant error in measuring non-sinusoidal voltages (with a "distorted" shape) is not significant in relation to the calibrator, since the calibrator, by definition, should generate a pure sinusoid (the harmonic coefficient should be minimal). Thus, the proposed solution allows you to implement high performance calibrator AC voltage. And the traditional methods have to solve the problem of measuring the rms values of an alternating voltage with a distorted shape, adding to the voltmeter circuit a more complex device - a converter of rms values. And in this case, the proposed structure makes it possible to derive certain advantages due to the implementation of procedures for the automatic calibration of the converter of effective values by signals from the output of the calibrator (in this case, the calibrator will be the “lead” and the effective values voltmeter). Such auto-calibration allows you to realize high long-term and temperature stability of the conversion of current values, even in those cases when it does not differ.

The design of high-voltage and high-frequency calibrators is significantly complicated by the need to work on a capacitive load (for example, the input capacitance of a tested voltmeter). The auto-regulation system based on the output amplifier of the calibrator should have a large gain at the highest frequencies of the operating range, a high slew rate of the output signal (up to 1400 V amplitude) and sufficient current to quickly recharge the capacitive load (100 pF - 200 pF, current 100-200 mA ) A "shortage" in any of these characteristics leads to a change in the set level of the output voltage when the load is connected, however, if a voltmeter "monitors" the output of the calibrator, compensation for the deviation is provided.

Thus, an additional auto-regulation loop made it possible to simplify the calibrator circuit and ensure high metrological characteristics and, in particular, expand the frequency range. The frequency response of the calibrator in the high-voltage range is limited due to the fact that parasitic capacitors (input capacitance of the amplifier, switching elements, mounting, etc.) are recharged through the high-resistance feedback divider, which reduces the speed of the circuit and, as a result, the frequency range . The possibilities of reducing the resistance of the high-voltage divider, as noted above, are limited by the error caused by the self-heating of the resistors of the divider by dissipated power. In the proposed calibrator, the error from the self-heating of the divider is eliminated by the control loop based on the voltmeter, and therefore the resistance of the divider can be reduced based on the required broadband.

USED BOOKS

1. "Global solutions in the field of accurate measurements."

Information Russified material of the company FLUKE (pp. 2-3, 24-25).

2. Electronics, 1982, No. 18.

L. Eccleston, N. Faulkner, N. Johnson, W. Prue, M. Timman “High-precision industrial voltage calibrator”, pp. 23-32, pp. 28-29 (DAC with PWM).

3. "Automatic measurements and instruments"

P.P. Ornatsky. Kiev, "Higher School", 1980 pp. 33-34 "Differential Measurement Method"; p.57 "Methods of increasing accuracy with minimal information on the nature and place of occurrence of the error"; p.140 "Voltmeter of average values".

4. "A device for checking voltmeters and calibrators B 1-18."

Technical description and operating instructions, part 1, 2.085.019 TO p. 34-36, 52 (differential voltmeter) p. 179 p. 10.4.2.1 “Table 10.1”.

5. "Voltage Converter 9-12".

Technical description and operating instructions, part 1, 2.008.006 TO page 8, clause 3.1.1.

Claims (3)

1. A wide-range calibrator controlled by a differential voltmeter, comprising a calibrator amplifier connected to the output terminal of the device with a scaling divider in the negative feedback circuit, a reference voltage source and a digital-to-analog converter (DAC) of this voltage, connected by its output to the input of the aforementioned amplifier and the analog-to-digital input a converter (ADC), the other input of which is connected to the input terminal of the differential voltmeter through an input scaling device of a differential voltmeter VA, while the ADC is installed with the ability to record its digital code in the DAC control circuit, characterized in that the output of the calibrator through the contacts of the switch is connected to the input of the differential voltmeter that controls it. 2. A wide-range calibrator controlled by a differential voltmeter according to claim 1, characterized in that the input of the calibrator amplifier is made in the form of a DAC voltage adder with an additional DAC voltage, which provides the formation of a correction signal, for which the output of an additional DAC through a weight resistor is connected to the summing input of the calibrator amplifier . 3. A wide-range calibrator controlled by a differential voltmeter according to claim 1, characterized in that it includes devices providing reproduction and measurement of an alternating voltage, in the form of a source of a reference voltage of an alternating current and a digital-to-analog converter of this voltage, which is connected via its output through the switch contacts to the input of the amplifier of the calibrator, and in the voltage measuring circuit is included, through the input device, an AC to DC converter, which its m output through the switch contacts connected to the measuring input of the ADC.

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