SU1582029A1 - Multiple-point digital thermometer - Google Patents

Abstract

The invention relates to temperature measurements and makes it possible to increase accuracy by reducing the effect on the measurement result of parasitic thermoEMF. The signals from thermoelectric converters (TP) 1 are alternately fed through switch 8 to the input of analog-digital converter 9, where they are converted into a digital code fed to computing unit 11. The temperature of the free ends of TP 1 is measured using resistance thermometers (TC) 2 at different directions of the measuring current generated by the stable voltage source 7, the switches 14, 15, the reference resistor 4, the load resistor 5. The final measurement result is formed in ychislitelnom unit 11 with the zero drift, and noise affecting a particular calibration curve TA. 1 il.

Description

The invention relates to temperature measurements and can be used in various industrial zones where temperature is measured with high accuracy.

The aim of the invention is to increase the accuracy of measurement by reducing the impact on the measurement result of parasitic thermoEMF.

The drawing shows the block diagram of the proposed digital thermometer.

The digital thermometer contains thermoelectric converters (TEC) 1, thermal converters 2 resistances (TS) located in a thermolimizer 3, an exemplary resistor 4, a load resistor 5, a stable voltage source 6, a capacitor 7, a switch 8, an analog-to-digital converter (ADC ) 9, memory unit 10, computing unit 1, key management unit 13, first lock-on switch 14 and second switch 15. The principle of the device operation is as follows:

The value of the measured temperature at an arbitrary temperature of the free ends of the TEC will be converted into thermoEMF, and the value of the temperature of the free ends of the TEC will be determined by the voltage drop on the corresponding terminals of the resistance thermocoupler. At the same time, the temperature measurement of the free ends of TEC will be performed in two readings, with different directions of current through the vehicle. In this case, in one case, the voltage value on the TC is summed with parasitic thermoEMF, and in the other, it is subtracted. Thus, the procedure of double measurements with reversible current direction ensures the elimination of all undesirable sources of errors in the measuring circuit of the vehicle (Peltier and Seebeck effects, bias voltages in the ADC input amplifier, etc.)

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Digital thermometer works as follows.

The switch 8 produces alternately circling all measuring channels. The code of the current channel number is i

The system is stored in memory block 10 and serves to specifically determine the order of processing the conversion result code of ADC 9 in accordance with the program stored in memory block 10, according to the functional purpose of each channel. Although the sequence of channel skirting may be different, it is necessary to ensure the following five cycles to obtain the temperature at the measured point. i

In the first cycle, the input of the ADC 9 is energized from the short-circuited input of the switch 8. The code from the output of the ADC 9 through the computing unit 11 enters the memory unit 10 and is used during further operation of the digital thermometer to compensate for the drift zero of the ADC 9 and interference measurement accuracy. In the first cycle, the control signal from the key management unit I3 is fed to the first control inputs of the first and second switches 14 and 15, connecting to the voltage source 6 and the reference resistor 4 of the load resistor 5.

In the second cycle, at the command of the computing unit 11, the control signal appears at the second output of the key management unit 13. In this case, instead of the load resistor 5, a capacitor 7 and a chain of series-connected resistance thermal converters 2 are connected to the source 6 of a stable voltage and the reference resistor 4. The switch 8 connects to the input of the A / D converter 9 potential outputs of the model resistor 4 and, by the voltage drop across it, the computing unit 11 determines the value of the current in the TC circuit and writes it to the second cell of the memory block 10,

In the third cycle of operation, the switch 8 connects to the input of the ADC 9 potential terminals of the TC of the measuring channel. The control signal remains at the second output of the key management unit 13. Computing unit 11 records the code corresponding to the sum (difference) of voltage drop on the vehicle and the parasitic thermoEMF acting in the measuring circuit at a given direction of the current to the third cell of the memory unit 10.

In the fourth cycle, the control CHI-switch at the third output of the key management unit 13 changes the current direction through the TC chain. The code from the output of the A / D converter 9 already corresponds to the difference (sum) of the voltage drop across the vehicle and the parasitic thermoEMF acting in the measuring circuit. Computing unit 11 extracts the code of the previous measurement from the third cell of memory 10, finds the arithmetic average of the results of two measurements, which corresponds to the voltage drop across the vehicle, determines the value of the vehicle resistance. Using the formula that establishes the relationship between its resistance and temperature (conversion characteristic is known), the temperature of the free ends of the vehicle is calculated. From the value of the temperature of the free ends, it is determined the thermopower code of the free ends for this type of TEC, which is recorded in the fourth cell of the memory block 10, i

In the fourth cycle, when a load resistor 5 is connected to a source of stable voltage and a sample resistor 4 by a key management unit 13 (in order to prevent self-heating of resistance thermocouples), the switch 8 connects to the input of the corresponding channel ADC 9 of the corresponding channel and the computing unit 11 by the measured thermoEMF code TEP 1, corrected for zero drift and interference, produces the addition of thermoEMF of TEC to thermal thermal flux of the free ends. Further, the computing unit 11 determines the value of $ 8,229 $ according to the conversion characteristic of the TEC;

Claims (1)

temperature of the temperature that enters the display unit 12. The formula was invented and the Multipoint, u F / Yu thermometer containing a thermoelectric converter, a circuit consisting of consistently connected resistance thermocouples, each 10 of which are located in the immediate vicinity of the free end of the corresponding thermoelectric converter, the switch, the inputs of which are connected to the outputs of the thermal converters 15 and potential terminals of the thermal converters of resistance cells, and the outputs are connected to the memory unit and the input of the analog-digital converter, 20 outputs of which are connected to a computing unit connected to a display unit and a memory unit, a capacitor connected to a circuit of series-connected thermal converters of resistance, a stable voltage source, the first terminal of which is connected to the first current output of the reference resistor, which potential terminals are connected 30 with switch inputs and a load resistor, characterized in that, in order to improve the measurement accuracy, the first and second switches, each consisting of three keys, and a key control unit, whose input is connected to the output of the computing unit, are introduced into it, and the outputs are connected to the corresponding control inputs of the keys of both switches, with the inputs of the keys the first switch is connected to the second output of a stable voltage source, and the inputs of the switches of the second switch are connected to the second current terminal of the sample resistor, while the output of the first switch of the first switch is connected through a load resistor to the output of the first switch of the second switch, and the outputs of the second switch the first switch and the third key of the second switch are connected to the input of the circuit from series-connected thermal conversions of resistance, the output of which is connected to the outputs of the third first key switch and the second key of the second switch. 35 50 55