SU714418A1 - Arrangement for determining the logarithm of the ratio of two voltages - Google Patents

Description

   , 1, the invention relates to the field of analog and computer technology and can be used in electronic measurement systems. Limes are devices for measuring the logarithm of the ratio of two voltages. One of these devices, f1, contains shouts, comparison circuits, differentiating chains, AND and OR elements, triggers, a counter, and counting pulse generators. The closest technical solution is a device 12 to determine the logarithm of the ratio of two voltages containing a comparison circuit, two capacitors, square pulse generator, pulse counter, three keys, the signal input of the first of which serves as the first input of the device. This device is based on the principle of forming, with a certain interval, a sequence of pulses, the number of which is proportional to the logarithm of the partial frequency of the smaller input voltage. A higher voltage at the beginning of the measurement cycle charges the first capacitor through the first switch. After a full charge, this capacitor begins to discharge before comparing with a lower input voltage, forming with the help of a generator the rectangular voltages of the second capacitor, second and third keys of a sequence of pulses, the number of which is proportional to the logarithm of the partial voltage of the larger voltage. A measurement error of such a device is obtained due to the leakage resistance of the capacitors, as well as from the instability of the operation of the comparison circuit. The pelting of the present invention is to increase accuracy. This is achieved by having a device for determining the logarithm of a ratio of two voltages, comprising a square pulse generator, a pulse counter, three keys, the signal input of the first of which is the first input of the device, the And element, two integrating RC-modules, the divider chats and the fourth the key, and the signal input of the second key is the second input of the device / outputs of the first and second keys, respectively, through the successively connected first integrating RC circuit and the third key, and through serially connected the second integrating RC circuit and the fourth key are connected to the first input of the element I, the output of which is connected to the input of the pulse counter, the control inputs of the first and second keys are connected respectively to 1C by the first and second outputs of the frequency divider, the first output of the square pulse generator is connected to the input of the divider frequency and the control input of the third key, the second output of the generator of rectangular pulses is connected to the control input of the fourth key on the second input of the element.

The block diagram of the device is depicted; in the drawing. . ,

The device contains the keys 1, 2, 3, 4, specherirue RC circuit 5, 6, the generator of rectangular pulses 7, the frequency divider 8 element 9 And, the counter 10 pulses.

The device works as follows. The input voltages Ux and Uy are fed to the halogen inputs of the corresponding switches 1 and 2, which are controlled by symmetrical pulses taken from the opposite outputs of the frequency divider 8 with a large division factor. The pulses 11 of the first and second outputs of the divider 8 are phase-shifted relative to each other by 180. The input signal of this divider is the pulse voltage of the forward pulse of the generator 7 rectangular pulses. Thus, the two shorts are 1 square U pulses with an amplitude equal to the input voltage DX, and the output voltage of the key 2 is straight A large 1st U pulses with an amplitude {equal to the voltage Uy, and two sequences of these pulsed voltages are in antiphase with each other.

The rectangular voltage of the key 1 is fed to the yodod of the integrating RC circuit 5, and the rectangular voltage of the key 2 is fed to the input of the integrating circuit 6. The output signals of the circuits 5 and 6 are triangular voltages Uj, varying in time exponential law. In the time interval from O to 1Zr, the voltage of RC-depi 5 to 3aBHCHMoCtH is determined by the time

om

-tltV

(l- "-e j-h-ptii -oiil,

and the voltage of the circuit is 6-tlT 0 and, e -h t i o-r1C.

Accordio lag theorem

time from It to 271 voltage of RC circuit 5

changed according to the law J-fT

  -ft / ni t-7t- -2ft, and the voltage of the circuit is 6. / - i g

-

,,) n u-l - 1t 2G From here the moment of comparison of stresses U n and in the time interval from O to 7t is determined by the dependence

,, VtnU,

and the moment of comparison of these voltages in the range from ZT to 2

(uk - “- and)

The output voltage of the RC circuit 5 is fed to the signal input of the switch 3, and the voltage of the circuit 6 to the signal input of the switch 4. These switches are controlled by impulse voltages that are out of phase with each other, which are removed from the opposite outputs of the generator 7 coal impulses.

Due to the fact that the outputs of the keys 3 and 4 are combined with each other and their output signal is fed to the second input of the AND element, which is capacitive, the input pulse voltage of the AND element will be symmetrical with respect to the zero level.

At the first input of the element I, a pulse voltage is applied, taken from the second output of the generator 7.

As a result of such control, only those pulses that are in the time interval from ti to tj are removed from the output of element 9. .

The number of these pulses is proportional to the difference (tj-ti), which equals the constant time constant of RC circuit 5 and RC circuit 6

V-b.- -evi- it.

The output pulses of the element And are fed to the input of the counter 10 pulses.

The use of new elements: an And 5 element, two integrating RC circuits, a TOTbi time divider, a key favorably distinguishes the proposed device for determining the logarithm of the ratio of two voltages from known ones, since the error is reduced due to the instability of the comparison circuit and the leakage of capacitors.

Claims (2)

1. USSR author's certificate number 547786, cl. G 06 G 7/24, 1976. 2. US patent number 324140, cl. 328-161, 1957 (prototype).