SU970133A1 - Digital temperature meter - Google Patents

Description

(54) DIGITAL TEMPERATURE METER

The invention relates to thermometry and can be used to create digital panel-mounted temperature meters working in conjunction with thermoelectric converters. A device for temperature measurement is known, which contains a voltage converter in a time interval, to one input of which a discrete controlled voltage source is connected, and to the output inputs of a digital voltage divider. The disadvantages of the known device are low non-polarization stability, manufacturing complexity and absence correction of the additive error component. Closest to the proposed technical entity is a device containing a primary temperature measuring transducer connected to the input of a voltage converter in a time interval whose output is connected to a switch, to the output of which a digital reading device is connected and to the input - output of a controlled divider frequencies, and to the control inputs, the outputs of the decoder connected to the digital reading device 2. However, in this device a large influence on the measurement result is additive error component which is reduced by the use of amplifiers with input channel modulation - demodulation. In addition, it has a relatively large insensitivity zone in the region of zero. The purpose of the invention is to improve the accuracy of temperature measurement by eliminating the additive component of the error. This goal is achieved in that a device containing a primary temperature measuring transducer is connected to one of the inputs of a switch connected by its output to one of the inputs of a voltage converter in a time interval, the control input of which is connected to the output of a reference frequency generator synchronized with network frequency, and with the input of the selector, the output of which through the linearization circuit is connected to the input of the digital reading device, and the control inputs of the switch, the selector and the linearization circuit with An additional selector, reversible counter, polarity indication unit and a bias voltage source connected between the connection point of the second output of the primary temperature converter c are connected to the corresponding outputs of the control unit whose signal input is connected to the output of the voltage converter in the time interval. the second input of the voltage converter in the time interval, while both inputs of the additional selector are connected respectively to the output of the reference clock generator additional simplicity and output control unit, and its two output terminals are connected respectively to the inputs of the subtractor and sulmiruyuschim down counter, its output connected to the other signal input of the control unit, one of the outputs, which is connected to the input of the indication unit polarity.

FIG. 1 shows a structural electrical circuit of the device; in fig. 2 - time diagrams of his work.

The device contains a primary measuring transducer 1, a switch 2, a bias voltage source 3) a voltage time interval converter 4, a reference frequency generator 5, a control block b, a selector 7, an additional selector 8, a reversible counter 9, 10 linearization, qi (wild a readout device 11, a polarity indication unit 12.

The primary measuring transducer 1 is connected to the input of the switch 2, one of the inputs of which is connected to one of the inputs of the voltage converter 4 through a source 3 of the voltage converter in a time interval. The output of the switch 2 is connected to the second input of the voltage converter 4 in the time interval connected by the output to the inputs of the control unit b, the outputs of which are connected to the inputs of selectors 7 and 8 "of the polarity indication unit 12, the linearization circuit 10 and the control input 2 The output of the oscillator 5 of the reference frequency is connected to the j 4 th voltage in the time interval and to the inputs of the selectors 7 and 8. Two of the additional selector 8 are connected to the summed-down and subtractive inputs of the reversible counter 9 / output of which connected to one of the inputs of the control unit. The output of the selector 7 is connected to the linearization circuit, which is connected to the input of the digital reading device 11.

The device works as follows.

In the initial state, the reversible counter is reset to zero. In the first measurement cycle, on a command from the control unit to the input of the voltage converter in the time interval, the switch connects the source of the bias voltage. The measurement of the voltage, D.d., is performed. For a time proportional to the output of the reference frequency generator, it is connected to the summing input of a reversible meter, as a result of which N pulses are recorded later.

CD

to (and

ABOUT,

N - T. f - ..

where T is the B15 interval, proportional; f is the pulse frequency of the reference frequency generator;

K is the conversion factor; U is the additive component of the error, reduced to the input.

In the second measurement cycle, the command from the control unit to the input of the voltage converter in the time interval is connected to the sum of voltages

(2)

U (T) i Ui,

C

cm

where and (T) is voltage. primary temperature transmitter output.

The voltage U is converted to a time interval. Simultaneously with the start of the second measurement cycle, pulses are sent to the subtracting input of the reversible counter from the reference frequency generator. The control unit records the moments of the reverse counter going through zero and the end of the formation of the time interval by the voltage converter in the time interval. In the interval between these events, by a command from the control unit. the reference generator output is connected to the input of the linearization circuit. If we consider that the reversible counter goes into the zero state after passing the input N. pulses to its subtraction, the frequency of the reference frequency generator is constant, then the time interval between the start, conversion and transition of the reversible counter through zero is TU (Fig. 2).

Tj T - T ,,, (3)

where T- is the transit time of the pulses to the input of the linearization circuit, or

L ,, - fo-NI-N K CHST) -SHile A-ism-l fcOa)

AND)

From expression (4) it follows that the result of measuring the voltage with a nervous measuring temperature transducer is devoid of an additive error component.

Claims (1)

After the corresponding conversion in the linearization scheme, the measurement result is displayed on a digital reading device. At the end of the measurement, the passage of pulses to the reversible counter is stopped. If temperatures above zero are measured, the voltage at the output of the primary temperature transducer is summed with the bias voltage, then. Td. 7 T. (5) The reversible counter goes through zero earlier than the second measurement ends, and on the command from the control unit, the display unit shows +. If temperatures are measured below zero, then the voltages U (. And U (T) are subtracted, or T T. (6) This means that the reversible counter goes through zero after the end of the second measurement cycle. In this case, the display unit polarity displays pag Sa6T -. To ensure normal operation, Ugrt is selected from the condition, (-T.) + D le "- /, (7) D" (-We) the voltage at the output of the primary temperature converter when measuring the maximum negative temperature; The value of the critical error component given to the input. For this choice of voltage, see When measuring positive and negative temperatures, it is possible to use one source of the reference voltage. In addition, the presence of the bias voltage makes it possible to reduce the insensitivity in the zero region to the level of discreteness. The advantage of the proposed device in comparison with the known one is that is the correction of the additive component of the path error of the analog-digital converter. This makes it possible to use as the last relatively inexpensive converters that are easy to manufacture and tune, do not require periodic drift correction of zeros during the operation period, which, in addition to improving accuracy, eliminates the need for instrument calibration. This advantage allows you to increase work productivity and measurement accuracy by several times, reduce the cost of self-construction, and also reduce operating costs. In addition, the indication of the polarity of the measured temperature is quite simple and with minimal hardware costs. A digital temperature meter containing a primary temperature measuring transducer connected to one of the inputs of a switch connected by its output to one of the inputs of a voltage converter in a time interval whose control input is connected to the output of a reference frequency generator synchronized with the network frequency and with the input of the selector, the output of which is connected through the linearization circuit to the input of the digital reading device, and the control inputs of the switch, selector and linearization circuit They are connected to the corresponding outputs of the control unit, the signal input of which is connected to the output of the voltage converter in a time interval characterized in that, in order to be biased. measurement accuracy by eliminating the additive component of the error; an additional selector, a reversible counter, a polarity indication unit and a bias voltage source connected between the connection point of the second output of the primary temperature transmitter and the second input of the voltage converter in the time interval are introduced; Both inputs of the additional selector are connected respectively to the output of the reference frequency generator and the additional output of the control unit, and its two outputs from are connected respectively to the summing and subtracting inputs of a reversible counter connected by its / output to another signal input of the control unit, one of the outputs of which is connected to the input of the polarity indication unit. Sources of information taken into account in the examination 1. The patent of France And 2125750, cl. G 01 K 7/02, 1972. 2. Kulikovsky KL, Shakhkam A.S., Shakhkam S. S. Methods for calculating the digital linearization scheme of the conversion function of measuring devices. Instruments and control systems, 1978, 8, p. 22-24 (prototype).