SU1721449A1 - Temperature meter - Google Patents

Abstract

The invention makes it possible to increase the measurement accuracy by linearizing the output signal of the device. High linearity is achieved by special selection of the resistance values of the passive arms of the bridge. The bridge contains two identical thermal resistances 1, 3, included in the opposite shoulders of the bridge, and two thermally independent balancing resistances 2, 4, included in the other shoulders. The value of one balancing resistance is chosen equal to 0.572 of the value of thermal resistance, the value of the other is 1.748 of the value of thermal resistance at 0 ° C. 1 il.

Description

 Yu

The invention relates to temperature measurement using platinum thermistors included in a bridge circuit.

Bridge circuits are known in which two identical thermistors are used to increase the sensitivity, which are connected to the opposite shoulders of the bridge.

However, they have a low linearity characteristics. For example, for linearization, it is proposed to include a thermo-dependent voltage divider in the circuit of a stabilized, power source.

The known bridge circuit contains two identical platinum resistive temperature transducers, included in the opposite arms of the measuring bridge, and two thermostable resistors, included in the other arms of the measuring bridge.

The circuit has a low linearity of the output signal.

The purpose of the invention is to improve the measurement accuracy by linearizing the bridge circuit.

This goal is achieved by the fact that in a temperature measuring device containing two identical platinum thermal converters connected in the opposite arms of a measuring bridge, the value of thermal-insulating resistors is chosen equal to 0.572 RO and 1.748 R0, respectively, where R0 is the resistance value of platinum thermal converters at 0 ° C.

The drawing shows a device for measuring temperature.

The bridge consists of two thermal resistances RiRs, having the same values of Rio Rso RO, included in the opposite shoulders, at t 0 ° C, and two constant thermo-sensitive resistors R2. R4, which are selected from the condition

R2 - 0.572 RO,

R4 1J48Ro, 0)

in this case the condition of balancing a place at zero temperature is ensured:

R2R4 Ro. (2)

The linearization of the bridge in case (1) is explained as follows.

The dependence of platinum wire resistances on temperature is as follows:

R R0 (1 +), (3)

v3 1 if i

where a 3,985 1 / hail; ft -5.876 1 / deg2. For the output signal of the bridge, U, with a constant current I, quadratic

Mr. on the parameter a t approximation, you can get the formula

U-IR0 (Ki at + K2 (at2)), where Ki and K2 are coefficients having the following form:

Ki

2 Re

2 RO + R2 + R4 c., -,, R2 + R4 + 2R0 (R2 + R4 + 2R0 2j3 / o2 0.074

0

five

0

5 0 5

0

five

0

five

From the condition Ka 0 we find: R2 + R4 2 1 ± J RO 2.32 Ro.

(6)

1-s

Solving the system of equations (6), (2), we obtain condition (1). When the values of resistance R2, R4 deviate from those indicated in this condition to a greater or lesser side, the nonlinearity coefficient K2 becomes different from zero, which means the appearance of nonlinearity in the bridge signal,

The nonlinearity parameter p K2 / Ki for the case of R2 R4 RO (prototype) is equal to 0.074.

For the values of R2 (0.565 ... 0.590) R0 (respectively, R4. (1.770;;, 1.695) RO), the parameter p is not more than 10% of the non-linearity of the circuit.

Outside this interval, the nonlinearity coefficient becomes large and the positive effect is not achieved.

The bridge contains two thermal resistances of 1.3 (Ri, Ra), included in the opposite shoulders of the bridge, having the same Rio Ra RO values at 0 ° C. two constant thermochip sensitive resistor 2.4 (R2, R4) and a stabilized current source 5. A recording device (not shown) is included in the measuring diagonal of the bridge.

The device works as follows.

To measure the temperature, platinum resistances 1.3 are placed in the test medium. Their resistances change, an imbalance occurs in the bridge, which is linearly dependent on temperature and measured by a recording device. The numerical calculations confirmed by the model experiment show that the root-mean-square measurement error associated with the nonlinearity of the bridge circuit decreases 8-10 times in the range (-100H + 100) ° C and 20-25 times in the range (50) ( +50} ° C, which means a corresponding increase in the accuracy of temperature measurement.

Claims (1)

A device for measuring temperature, containing two identical platinum resistive temperature transducers, included on the opposite shoulders of a measuring bridge, and two thermally independent resistors, included on the other shoulders of a measuring bridge, different In order to increase the measurement accuracy by linearizing the output signal of the device, the value of the temperature-independent resistors is chosen to be 0.572 R0 and 1.748 RO, respectively, where RO is the resistance value of the platinum resistive temperature transducer at 0 ° C.