SU974577A1 - Method and apparatus for measuring dc voltage - Google Patents

Description

(54) METHOD OF MEASURING DC VOLTAGE AND DEVICE D. THIRD OF ITS IMPLEMENTATION.

The invention relates to information-measuring technology and can be used both in automatic control systems and in digital measuring instruments for universal and special purposes.

Methods for measuring DC voltages and apparatus for their implementation are known.

There is a known method for measuring DC voltage, which is based on an intermediate conversion into a time interval by integrating the reference voltage until the integrated voltage reaches the measured voltage, then converting it into a code by filling it with pulses at an exemplary frequency, and The method comprises a reference voltage source, keys, an integrator, an initial value setting device, a comparator, a comparison device, a control unit, a generator pulses of exemplary frequency, the circuit And the counter f1.

The disadvantages of the method and device for its implementation are the lack of noise immunity and low

conversion accuracy. This is due to the fact that this method measures instantaneous voltage values with a superimposed AC noise signal and that the conversion function has a constant integration time value, the stability of which is associated with significant workloads.

The closest in technical essence to the present invention is a method for measuring DC voltage, based on an intermediate conversion into a time interval in which the measured DC voltage is integrated during a time interval equal to an integer number of periods of the interference signal.

20 alternating current, and then integrate the reference voltage, the polarity of which is opposite to the polarity of the measured, with the subsequent conversion of the time interval into the code

25 by filling with pulses of an exemplary frequency I 2.

An apparatus for carrying out the method comprises a voltage source, the output of which is connected to the first input of the first switch, the second

Input 30 through which the unit for integrating the reference voltage is connected to the output of a comparator, the first input of which through the integrator is connected to the outputs of the first and second keys, the first output of the second key is connected to the input cell, and the second input through the successively connected devices for forming the integration period of the measured voltage and pulse generator of exemplary frequency, which form the control unit, is connected by the first input of the counter, the second input of which is connected through the I element to the output The pulse generator of the exemplary frequency and the second input of the first key, the comparator device 3. The disadvantage of the method and device for its implementation, chosen for the prototype, is the low speed and low accuracy of the measurement of the dc voltage. This is due to the fact that the measurement time is always longer than a time interval that is a multiple of the integer number of periods of the signal of the alternating -th wave, and depends on the magnitude of the measured voltage, since the integration of the measured and reference voltages is not aligned in time. In addition, the additive error caused by the zero drift of the DC amplifiers used in the integrator and the comparison devices is significant, since it is proportional to the measurement time. The purpose of the invention is to increase the speed and increase the accuracy of measurement. The goal is achieved by the method of measuring DC voltage based on an intermediate conversion into a time interval in which the measured DC voltage is integrated over a time interval equal to an integer number of periods of the AC noise signal, and then integrated the reference voltage, the polarity of which is opposite to the polarity of the measured, with the subsequent conversion of the time interval into a code by filling with pulses of the reference frequency, during the time interval and equal to an integer number of signal periods alternating current interference simultaneously with the integration of the measured voltage DC TQKB umenshayuschees formed linearly on the magnitude of the reference voltage to zero voltage is measured at equal emomu voltage d.c. begin integration reference voltage. A device for carrying out the method comprising a voltage source, the output of which is connected to the first input of the first key, the second input of which is connected to the output of the comparator through the integrator through the integrator through the integrator, The first input of the second switch is connected to the input terminal, the second input is connected via a serially connected device to form the integration period of the measured voltage and the pulse generator. in the reference frequency, which form the control unit, is connected to the first input of the counter, the second input of which is connected to the output of the pulse generator of the reference frequency and the second input of the first key, the comparator, the generator of linearly varying voltage, the input of which is connected to the input the pulse generator of the exemplary frequency, and the output - with the first input of the comparator, the second input of which is connected to the second input of the second key, and the output - to the control input of the period formation unit integrated Rovani reference voltage. FIG. 1 is a timing chart explaining the principle of the method of measuring DC voltages) in FIG. 2 is a block diagram of an apparatus for carrying out the method. FIG. 1 shows a linearly varying voltage 1, a measured DC voltage 2, an integrated voltage 3, an integration time of the measured DC voltage 4, an integration voltage of the reference voltage 5. A device for carrying out the method shown in FIG. 2, contains an integrator b, built on an operational amplifier with a capacitive feedback, switches 7 and 8 for connecting to the integrator input the reference voltage of the source of the reference voltage 9 and the bus 10 of the measured DC voltage, the comparator 11, the comparator 12 , the generator of linearly varying voltage 13, the control unit 14 with the device 15 forming the integration period of the measured voltage and the generator 16 pulses of the reference frequency, the unit 17 forming the period of integration of the reference voltage, bus Sto 18, Start bus 19, AND gate 20 and counter 21, the output of which is removed -Digital code measurement result. The method of measuring the DC voltage occurs in two cycles. During the first cycle, the measured DC voltage 2 is integrated and a linearly varying voltage 1 is formed, the slope of which is such that over a time interval T equal to an integer number of periods of the AC interference signal, it varies from the value of the reference voltage to zero. At the moment of equality of the linearly varying voltage 1 to the measured voltage of the direct current 2, the first cycle ends. For the first clock cycle, the following relations u (t) are valid. о Т М - у - reference voltage / У - measured voltage of alternating current 2; —the duration of the first cycle T — the time interval equal to an integer number of periods of the signal of an alternating-current disturbance and (t) —integrated voltage 3, t — is the constant of the integration time. From these equations, it follows that the first cycle measure t, is equal to - CR - them. and the value of the integrated 3 at the end of the first cycle is expressed as lift LM tcrc xi; -. During the second cycle, a joint integration of the measured voltage of the direct current of the reference voltage, the polarity of which is opposite to the polarity and measurable, takes place. The second cycle, whose duration is denoted by t, ends when the integrated first and second cycles are integrated. Then you can write the equation from which the second cycle time, i.e., the integration time of the reference voltage 5, equals the time interval converted into a code by filling it In pulses of the exemplary frequency, the final measurement result will be written as N ilb.I,

where N is digital

T is the period of following pulses of the reference frequency. The measurement cycle time, -) limited by the duration of the first and second cycles, i.e. the integration time of the measured DC voltage 4, is equal to

Uo- Ux

Jk

t t

T T

UD

Claims (3)

The operation of the device for carrying out the method takes place in two cycles as follows. When a start 19 pulse arrives at the shik, the start pulse is reset to zero and the counter 21 is started and the generator of 16 pulses of the reference frequency of the control unit 14 is started. As a result, the pulses of the exemplary frequency arrive at the device for forming the integration period of the measured voltage, which forms a time interval T with the duration equal to an integer number of periods of the alternating current interference signal and connects the input 10 of the measured voltage to the input of the integrator 6 DC couplings. Simultaneously, the generator of the linearly varying voltage 13 is turned on from the starting pulses, the output voltage of which during the time interval T varies from the value of the reference voltage to zero. The first cycle ends when the voltage at the generator output of the linearly varying voltage becomes equal to the measured voltage applied to the bus 10. At this moment, the comparison device 12 generates a pulse, according to the signal of which the voltage-integrating period 17 of the reference voltage is connected via switch 8 the source of the reference voltage is fed to the integrator input. The measured and reference voltages are jointly integrated. The second clock ends when the integrator's output voltage b is equal to the threshold of the comparator 11. On bus Stop 18, a pulse is generated, on a signal from which the block 17 of forming the reference voltage integration period disconnects the reference voltage from the integrator input. At the same time, the measured voltage is disconnected from the integrator input, since the formulas given show that the time of the first and second cycles is equal to the integration time of the measured voltage. During the second cycle, i.e., the integration time of the reference voltage, the pulses from the generator output 16 pulses of the exemplary frequency through the element 20 enter the counter 21, with the result that at the outputs of the counter a measurement result is formed - a digital code directly proportional to the measured one direct current voltage. Thus, the proposed method for measuring DC voltage and a device for carrying it out reduces the measurement time to a value equal to an integer number of periods of the AC interference signal and reduces the additive error caused by the drift of the dc amplifiers. the integrator and the comparison devices in the practical implementation of the method, as this error is directly proportional to the measurement time. Using the proposed method for measuring DC voltages and a device for its implementation distinguishes them from the prototype, for example, for the maximum measured voltage, a 2-fold increase in speed and an increase in measurement accuracy by 50% will allow more accurate measurement of the voltage constant current in a shorter time, which is especially important when measuring low-voltage stresses from several sensors. Claim 1, A method for measuring DC voltages based on an intermediate conversion to a time interval in which the measured DC voltage is integrated over a time interval equal to an integer number of periods of an AC disturbance signal, and then integrating the reference voltage, the polarity of which is opposite to the polarity of the measured, - with the subsequent conversion of the time interval into a code by filling with pulses of an exemplary frequency, characterized in that, in order to increase performance and improvement of measurement accuracy, for a period of time equal to an integer number of signal periods, the alternating current disturbances, simultaneously with the integration of the measured DC voltage, form a linearly decreasing from the value of the reference voltage to zero, the voltage of which is equal direct current integration begins to integrate the reference voltage. 2. An apparatus for carrying out the method according to claim 1, comprising a source of a reference voltage, the output of which is connected to the first input of the first key, the second input of which is connected to the output of the comparator through the integrator through the integrator the first and second keys, the first input of the second key is connected to the input terminal, the second input is connected via a serially connected device to form the integration period of the measured voltage and the pulse generator cos exemplary frequencies that form the control unit, connected to the first input of the counter, the second input of which through AND gate connected to the output reference frequency pulse generator and a second input of the first key; Comparison device, characterized in that a generator of linearly varying voltage is inputted, the input of which is connected to the input of the exemplary frequency pulse generator, and the output is connected to the first input of the comparison device, the second input of which is connected to the second input of the second key, and the output to the control the input unit of the formation period of the integration of the reference voltage. Sources of information taken into account in the examination 1.Shushkov EI, Tsodikov MB Multichannel analog-to-digital converters. L., Energie, 1975, p. 37, 48-51. 2. Gitis E.I. Information converters for electronic digital computing devices. M., Enery, 1975, p. 368-374 (prototype). 3. USSR author's certificate number 347910, cl. H 03 K 13/20, 4.09.72 (prototype).  t m.f 1