DE2710782A1 - Temp. difference meter with single channel circuit - is connected to linearised thermistor network transducers using single supply - Google Patents

Abstract

A temp. measurement device is for measuring temp. differences and permits single channel difference measurements and automatically produces digital measurement results. It is also designed to operate from a single voltage source, e.g. of 6 volts. A linearised thermistor network is used as the transducer and has highly accurate thermal resistance characteristic and reproducibility. An optional number of thermistor networks (10, 11, 12) may be used with a single channel. They are supplied with current from a battery which also supplies the associated circuitry and operated below self-heating current levels. One thermistor is a metal plate type with its O degree cartridge equal to that of the other networks.

Description

Temperature meter

The invention relates to a temperature meter for measurement of temperature differences.

So far, temperature differences have mainly been measured analogously and the result obtained is then converted into a digital value by means of an AD converter. For this, however, several operational amplifiers had to be used, not only the circuit complexity increased, but also the susceptibility to failure. the Required reproducibility due to the drifting of the related operational amplifiers an ongoing zero adjustment.

A heat meter is known from German Offenlegungsschrift 1 801 554 become, the temperature-dependent resistances in each case on the heat-emitting surface attached, which are traversed by the current, the size of which is a measure of the is the amount of heat given off and is evaluated in a counter. The temperature-dependent Resistors are connected to a voltage associated with the size of the heat-emitting area. This heat meter should always, regardless of the size of the heat-emitting surface allow equally large temperature-dependent resistances for use.

This known arrangement uses alternating current to generate the sensor current, which is known to be up to, depending on the permissible voltage fluctuations Can fluctuate + 10%. Accordingly, of course, can not be of a reliable one and high measurement accuracy. In addition, this measuring arrangement is from Existence of an alternating current network dependent and depending on the dimension of the radiator different resistors must be used in each case.

The present invention is based on the object of a temperature meter to create that allows a single-channel differential measurement and as a measurement result automatically ejects a digital measured value. Furthermore, the heat meter according to the invention from a single voltage - for example 6 V - can be operated.

The above problems are achieved in that as a donor linearized thermistor networks are used, their resistance temperature dependence and reproducibility is highly accurate and has tight tolerances.

Further measures of the invention are in the claims and the description set and shown in the drawing using an exemplary embodiment. The only Figure of the drawing shows the block diagram of a digital temperature converter.

The embodiment of the invention shown in Fig. 1 shows the Thermistor networks 10, 11, to each of which the fixed reference voltage Uref 1 i via an operational amplifier circuit and the associated analog switch 13 are applied is, wherein the sequence control device 20 turns on the analog switch 13. the subsequently connected constant current injection device 14 supplies one of the Temperature inversely proportional to the constant charging current for a capacitor 15. The capacitor discharge switch 16 is now opened by the sequence control device 20, and it begins to build up a voltage across the capacitor 15, which increases linearly with Time grows.

The capacitor voltage is fed to a comparator 17.

If the capacitor voltage reaches the one set on the comparator 17 Reference voltage Uref 2 'so the latter switches and stops the counter 18, which was started at the moment in which the capacitor discharge switch 16 opened was or

the capacity for constant current charging has been released, and at the same time the sequence control device 20 switched the counter 18 to the "counting up" position Has.

With the correct choice of the counter clock frequency or the frequency of the crystal generator 19 and suitable definition of the sensor voltage Uref 1 and appropriate selection of the capacitor and the reference voltage Uref 2 is achieved in the measurement result, that each digital counting step has a defined value in the decimal scale of the temperature measurement is equivalent to. So it is, for example, with the elements of the current state of the Technology possible, with the present invention a temperature value of 0 to + 0.1 ° K Maintain accuracy digitally.

In this way, an effective temperature measurement becomes a time measurement, because the time is measured which elapses until the capacitor voltage opens of the associated discharge switch 16 reaches the comparator reference voltage Uref 2 Has.

A constant value is now contained in the digital result obtained, which depends on the size of the capacitor 15 and the two reference voltages Uref 1 and Uref 2 'where the constant value is proportional to the voltage Uref 2 and inversely proportional to the voltage Uref 1 and also proportional to the resistance value of the linearized thermistor network 12 at 00 C = 2730 K.

The digital result also includes the one on the temperature sensor 10 (S1) included lower temperature value, which in turn is proportional the capacitance C and the reference voltage Uref 2 and inversely proportional to the Reference voltage Uref 1, but also proportional to the slope of the resistance temperature line of the linearized thermistor network.

After receiving the measurement result corresponding to the lower temperature the same measurement is made with a second temperature sensor (RMF 2) in the second thermistor network 11, which is exposed to the higher temperature, now performed by the sequence control device 20 the sensor voltage Uref 1 to the thermistor network via the switch 13 (S2) 11 is placed and via the same constant current impressing 14 the same capacitor 15 is charged as described above.

This time, however, the start-stop counter 18 is in the "counting down" position switched.

The digital counting result now only contains one value, which is directly proportional to the temperature difference between the two temperature sensors prevailing different temperatures. The constant of proportionality here is proportional to the reference voltage Uref 2 and inversely proportional to the sensor voltage Uref 1 and proportional to the capacitance C as well as proportional to the slope of the Resistance temperature lines of the linearized thermistor networks 10, 11 etc.

With a suitable selection of the capacitor 15, the accuracy of the The measured value only depends on the change in the slope value of the resistance temperature line to be influenced. A drift in the voltage supply would affect the accuracy of the measurement result have no influence, since the voltages Uref 1 and Uref 2 can be derived from the same power supply and Uref 2 in the counter and Uref 1 stand in the denominator of the expression for the constant of proportionality.

The invention now provides a value for the temperature difference given in digital form. It is now also possible to determine the temperature of a of the two sensors 10 and 11 can also be measured absolutely. For this purpose is called third linearized thermistor network 12 a metal film resistor Ro is provided, whose value is the resistance value of the two same linearized prevailing at OOC Thermistor networks 10, 11 is the same. Here is first about the flow control 20 and the switch SO, the sensor voltage Uref 1 is applied to the resistor Ro 12 and according to the method described above, a digital count of the on position "Counting up" switched counter 18 received. In the second measuring step the Sensor 10 or 11 via switch S1 or S2 of switching unit 13 to Uref 1 placed and the counter 18 switched to the "counting down" position. The received The digital counting result is now the effective temperature at the sensor.

The invention allows virtually any number of sensors 10, 11, 12 .... n, all of which are located on the same measuring channel or their temperature differences or their absolute temperature determined according to the invention via the same channel can be.

The invention is also based on the principle that the through the measuring current flowing through the sensor never exceeds the value the could lead to self-heating of the sensor, i.e. the sensor voltage Uref 1 is set so that the sensor current for the highest temperature to be measured remains below the self-heating value.

The invention can be used, for example, as a heat meter. In this case, the sequence control of the impulses in the feed pipe is a Heating etc. of the impeller counter started. The time interval between the impeller impulses is a measure of the flow rate. According to the invention, it is advisable to use the temperature difference measuring circuit as well as the associated sequence control with counter and quartz generator from a single one Battery operate. Since the time interval between the impeller counting pulses is relative is large, you only need the analog part of the measuring circuit to the voltage source to lay when such an impulse arrives. This will only save the battery for a short time noticeably stressed and the service life of the battery and the functionality of the Device significantly increased. The sequence control and the counter, however, can in C-MOS technology and because of the extremely low power consumption always be connected to the battery supply.

Patent claims: Blank page

Claims (5)

Claims 1. Temperature meter for measuring temperature differences, as a result, linearized thermistor networks are used as sensors (10, 11, 12) are used, their resistance temperature dependence and reproducibility is highly accurate. 2. Temperature meter according to claim 1, characterized in that g e k e n n -z e i c Note that any number of thermistor networks (10, 11 ... n) are on the same Measuring channel lies. 3. Temperature meter according to claims 1 and 2, thereby g e k e n n z e i c h n e t that the voltage of the thermistor network (10) is set is that for the highest temperature to be measured, the current of the sensor is below the Self-heating value remains. 4. Temperature meter according to one or more of the preceding claims 1 to 3, in that the linearized thermistor networks with the downstream functional elements supplied with power from a battery will. 5. Temperature meter according to claims 1 to 4, characterized g e -k e n n n z e i c h n e t that one of the linearized thermistor networks (12) as Metal film resistor is formed, the value of which is that prevailing at 00 ° C Resistance value of the other linearized thermistor networks (10, 11 ... n) equal is.