GB2074734A

GB2074734A - Method and apparatus for measuring temperature

Info

Publication number: GB2074734A
Application number: GB8037728A
Authority: GB
Original assignee: Atmos Fritzsching and Co GmbH
Current assignee: Atmos Fritzsching and Co GmbH
Priority date: 1980-04-21
Filing date: 1980-11-25
Publication date: 1981-11-04
Also published as: FR2480939B1; FR2480939A1; DE3015310A1; GB2074734B

Abstract

An electronic thermocouple meter has a thermocouple element (10) producing a temperature-dependent voltage which is fed to an amplifier (12). The voltage produced by a compensating element (18) is fed to an amplifier (20) and the outputs of said amplifiers (12, 20) are added by an adding circuit (22). In order to increase the precision of the measurement, the compensating element (18) is used for the temperature measurement instead of the thermocouple element which is electrically short-circuited. <IMAGE>

Description

SPECIFICATION Method and apparatus for measuring temperature The present invention relates to a method of measuring temperature using an electronic thermocouple meter in which the voltage produced by a thermocouple element housed in a temperature sensor and the voltage produced by a compensating element are added, and to apparatus for measuring temperature by this method.

Thermocouple meters are widely used for measuring temperatures. However, these meters are only conditionally useful for air-conditioning purposes, because for these purposes they would need to satisfy inter alia the following desiderata: a) Short response time even in slowly moving air b) Utmost precision (frequently better than + 0.5 K) c) Robust construction and simple operation d) Low purchase price.

Most customary thermocouple meters fail to satisfy particularly the condition as to precision, because their precision is limited by the tolerances of the thermocouple elements and of amplifiers connected in series to said elements.

it is an object of the invention to increase the precision of measurement of the temperature sensor without thereby necessitating a modification of the existing electronic meters or the purchase of new meters, so that the same meter, which may possibly be present already, can also be used simultaneously for air-conditioning.

According to the present invention the compensating element is used for the temperature measurement instead of the thermocouple element.

Because measurements are only performed with a comparatively narrow temperature range in air-conditioning, it is thus possible to utilise the high precision, for example, of a pyroelectric conductor component, which is also cheaper than a thermocouple element.

In a preferred embodiment of the invention the compensating element is housed in the temperature sensor and the connections for the thermocouple element are electrically short-circuited. The compensating element can thus be brought, like a thermocouple element, to a remote measurement station, and the tolerances of the thermocouple element circuit are eliminated, which increases the precision of the measuring device.

An embodiment of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a block circuit diagram of a known thermocouple meter, and Figure 2 shows a block circuit diagram of a temperature-measuring instrument of the present invention.

Fig. 1 shows a known thermocouple. meter in which a thermocouple element 10 delivers a voltage to an input amplifier 1 2. The output voltage U1 of the amplifier 1 2 is proportional to the temperature difference between the "hot junction" 1 4 at temperature T1 and the "cold junction" 1 6 at temperature To of the thermocouple 10.

Therefore: U1 = K (T1-To) Near the cold junction 16, and therefore at the same temperature To, there is a temperature-dependent component, e.g. an NTC pyroelectric conductor 1 8. By an appropriate circuit, which comprises inter alia an amplifier 20, a further voltage U2 is produced which is proportional to the temperature To of the cold junction. Conveniently, the constant of proportionality is chosen to be equal to that of the thermocouple circuit. Thus: U2 = K.To The two voltages U1 and U2 are then fed to an adding circuit 22 in which they are algebraically summed. The output of the adding circuit therefore delivers the following voltage U3 U3 = U1 + U2 = K(T1-To) + K.To = K.T1 The voltage U3 is therefore proportional to the temperature T1.

It is clear that the tolerances of the thermocouple element 10 and of the input amplifier 1 2 have a predominant influence on the measurement result. These tolerances are unavoidable with the use of thermocouple elements.

Fig. 2 shows a circuit diagram of an embodiment of the invention in which, instead of a thermocouple element, a highly conductive, thermoelectrically neutral copper yoke 24 is connected to the input of the amplifier 1 2.

Accordingly, the voltage U1 at the output of the amplifier 1 2 always remains at "0" irrespective of the temperature. The rest of the circuit is the same as that shown in Fig. 1.

Under these circumstances the following voltage U3 appears at the output of the adding circuit 22: U3 = U1 + U2 =0 + K.To = K.To This output voltage U3 is completely free from the deficiencies of the thermocouple circuit, because the latter is short-circuited. The voltage U3 is therefore a function only of the temperature of the compensating element 1 8.

Now, with the apparatus according to the invention, the compensating element is brought by appropriate wires to the position of the hot junction previously used. The voltage U3 is then a linear function of the temperature prevailing at the measurement point.

With the apparatus according to the invention, the entire temperature sensor can be wired so that it already contains the shortcircuit yoke 24. It is thus possible to change from the one type of measurement to the other without further modification of the ac tual electronic meter simply by removing the thermocouple test sensor and plugging in the NTC test sensor. This results in a considerable economy because the two types of measure ment can be performed by the same meter by use of a different temperature sensor.

Claims

1. A method of measuring temperature using an electronic thermocouple meter in which the voltage produced by a thermocouple element housed in a temperature sensor and the voltage produced by a compensating element are added, characterised in that the compensating element is used for the temperature measurement instead of the thermocouple element.

2. Apparatus for measuring temperature by a method according to Claim 1, characterised in that the compensating element is housed in the temperature sensor and that the connections for the thermocouple element are electrically short-circuited.

3. Apparatus for measuring temperature substantially as hereinbefore described and as illustrated in Fig. 2 of the accompanying drawings.