GB2121181A

GB2121181A - Non-contact sensing of surface temperature of objects

Info

Publication number: GB2121181A
Application number: GB08214667A
Authority: GB
Inventors: Laszlo Urmenyi; William Robert Urmenyi
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-05-20
Filing date: 1982-05-20
Publication date: 1983-12-14
Also published as: GB2121181B; DE3313487C2; DE3313487A1

Abstract

A member 2 in the vicinity of an object 1, has an opening leading to a protective enclosure 3 in which a temperature sensing element 4 is on mounted. Means 6 are provided to suck the ambient fluid, usually air, from the surface of the object into the protective enclosure, whereby the temperature sensing element 4 takes up the fluid temperature, providing a fluid temperature signal. The fluid flows in the gap between the object and the member before entering the opening and takes up a temperature between the object temperature and the member temperature. A second temperature sensing element 5 takes up the temperature of the member 2 providing a member temperature signal. Electronic means 8 combine the fluid temperature signal and member temperature signal in such a manner as to obtain an object temperature signal 10 which is a function of the surface temperature of the object unaffected by the temperature of the member. A diffentiator may be added which provides a signal which is a function of the rate of change of the fluid temperature and is combined with the fluid temperature signal and the member temperature signal to obtain an object temperature signal response of reduced time constant. <IMAGE>

Description

SPECIFICATION Improvements in non-contacting measurement of surface temperature This invention refers to the non-contacting measurement of the surface temperature of objects.

It has been suggested to measure the temperature of moving metal foil by mounting a temperature sensing element in a protective enclosure near the metal foil and using means to suck air from the foil surface into the enclosure, the temperature sensing element producing an electric signal which is a function of the temperature of the air entering the enclosure, which closely follows the foil temperature. The purpose of this proposed device was to apply the electric signal to an eddy current type foil thickness measuring device in a manner to compensate the influence of foil temperature variations on the foil thickness measurement. The proposed enclosure was part of an essentially plane member adapted to be mounted in the vicinity of and parallel to the moving metal foil so that the pumped air flows in the narrow gap between the foil and the said member.It was found that initially, when the said member is still cold, the air entering the enclosure does not quite reach the foil temperature but is cooled by the said member, the air temperature being essentially the arithmetic mean between foil temperature and member temperature. It was also found that when the foil temperature changed rapidly, there was some time delay till the temperature sensing element followed.

The object of the present invention is to provide non-contacting means to obtain an electric signal which is a function of the surface temperature of an object of any shape, free from the above mentioned disadvantages.

A further object of the invention is to provide means to obtain a temperature read-out in any convenient temperature scale from the above signal.

According to the invention, non-contacting means are provided to obtain an electric object temperature signal which is a function of the surface temperature of an object, comprising a first temperature sensing element mounted in a protective enclosure, a member adapted to be brought in the vicinity of the object, the shape of part of the surface of the said member being such that when it is in the operating position a gap is formed between the object and said member, said member having an opening leading to the said protective enclosure, pumping means adapted to suck the ambient fluid, usually air, from the surface of the object into the protective enclosure whereby the first temperature sensing element takes up the temperature of the inflowing fluid providing an electric fluid temperature signal, a second temperature sensing element adapted to sense the temperature of said member providing an electric member temperature signal, and means to combine the signals obtained from the two temperature sensing elements in a manner that the said electric temperature signal is obtained which is a function of the surface temperature of the object, unaffected by the temperature of the said member.

Also, according to the invention, means are provided to obtain a further electric signal which is a function of the rate of change of the fluid temperature signal, and means to combine the said further electric signal with the fluid temperature signal to obtain an object temperature signal of reduced time constant.

Also according to the invention means are provided to obtain from the object temperature signal a temperature read-out.

Also according to the invention, when greatest accuracy of measurement is required, electrical means may be provided to heat at least part of the member facing the object essentially to the temperature of the fluid sucked into the protective enclosure.

Alternatively, the member may be heated to a temperature which is preferably at least as high as the maximum temperature reached by the object and means are provided to keep the temperature of the member constant.

The object temperature signal may be utilised in various ways. E.g. it may be used in conjunction with an eddy-current type foil or sheet thickness measuring device to compensate for the effect of temperature variations of the foil or sheet on the measurement or in conjunction with any process where temperature variations are important.

Actual temperature read-out is not always required. Alternatively it may be utilised to obtain a temperature read-out.

The invention will now be more fully described by the way of examples with reference to the accompanying drawings in which Fig. 1 is an example of the invention applied to a plane object.

Fig. 2 is an example of the invention applied to a cylindrical object.

Fig. 3 is a block diagram of an example of the electronic circuit of the invention employing one resistance thermometer with positive and one thermistor with negative temperature co-efficient.

Fig. 4 is a block diagram of an example of the electric circuit of the invention employing two resistance thermometers both having positive or both having negative temperature co-efficients.

In Fig. 1, 1 is the object, e.g. aluminium foil, moving in the direction of the arrow, 2 is the member, 3 is the protective enclosure, 4 is the first temperature sensing element, e.g. a platinum wire thermometer, 5 is the second temperature sensing element, 6 is pumping means adapted to suck air from the surface of the object via tubing 7, 8 is an electronic device as shown in detail in Fig.

3, or 4, 9 is a heating element adapted to heat the surface of member 2 facing the object 1, 1 6 are leads carrying the current to 9, 10 is the output of 8 being the object temperature signal and 11 is means to provide the object temperature read-out.

In this example the object is plane and so is the surface of the member facing the object, in the operating position the surface of the member being essentially parallel to the object. The surface of the member may be slightly curved, the distance between member and object being smaller near the centre than near the edge. The air flows in the latter case slower near the edge than near the centre. Heating element 9 is optional and is only used when greatest accuracy of measurement is essential. Temperature readout 11 is also optional. In operation air flows in the gap between 1 and 2 and takes up a temperature between the temperature of 1 and 2. 3 takes up the temperature of the air and Stakes up the temperature of the member.The electronic circuitry of 8 provides an output signal which is a function of the temperature of the object 1 unaffected by the temperature of member 2.

Details of an example of the block diagram of the circuit are described with reference to Figs. 3 and 4. In Fig. 2, 1 is part of the object, e.g. a cylindrical rotating shaft, 2 is the member, which has a cylindrical surface, which, when in the operating position, may be concentric with 1, or may be slightly eccentric, the distance being smaller near the centre. Numerals 1 to 11 denote identical parts to Fig. 1 and are self explanatory.

In Fig. 3, 4 is a resistance thermometer, e.g.

platinum wire, having a positive temperature coefficient, 5 is a thermistor having a negative temperature co-efficient, 1 8 is a resistor, 12 is a signal conditioning amplifier, 1 7 is a differentiator, 15 is a summing amplifier, 10 is the output, 11 is a temperature read-out device. This example is suitable when only limited accuracy is required.

The thermistor on its own has a non-linear characteristic, but with a resistor of suitable value connected parallel to the thermistor, an approximately linear characteristic can be obtained over a wide temperature range. In operation, the fluid temperature being essentially the arithmetic mean between object temperature and member temperature, when the fluid temperature and member temperature are equal, then the fluid temperature must be equal to the object temperature. But when the member temperature is lower than the fluid temperature, then the resistance of 5 is greater and the cooling effect of the member on the fluid is compensated.

The output of 1 2 is therefore a linear function of the object temperature unaffected by the member temperature. The differentiator 1 7 produces an output proportional to the rate of change of the output of 12 and added to the output of 12 by means of summing amplifier 1 5 an output 10 of reduced time constant is obtained. 11 is a device giving a temperature read-out.

Referring now to Fig. 4, 4 is a temperature sensing element adapted to measure the temperature of the fluid, usually air, 5 is a temperature sensing element adapted to measure the temperature of the member, both temperature sensing elements having a positive temperature co-efficient, 12 and 1 3 are signal conditioning amplifiers, 14 is a difference amplifier also providing power for heating element 9, 1 5 is a summing amplifier, 1 6 is a difference amplifier, 17 is a differentiator. Heating element 9, difference amplifier 1 4 and differentiator 1 7 are optional. If 1 7 is not used, 1 5 becomes superfluous. 10 is the output and 11 the temperature read-out.

The operation of the circuit is best explained by the way of a numerical example. Let us assume that the object temperature is 1 000C and the member temperature is 600C. Then the fluid temperature will be 80"C. If the output of 1 3 is proportional to twice the fluid temperature, i.e.

1 600C and the output of 12 is proportional to the member temperature i.e. 600 C, then, disregarding summing amplifier 15, the inputs to difference amplifier 1 6 are proportional to 1 600C and 600C respectively, and the output of 1 6 is therefore proportional to 160 - 60 = 1000C i.e. the object temperature, unaffected by the member temperature.

Differentiator 1 7 produces an output proportional to the rate of change of fluid temperature and is added to the output of 13 in order to reduce the time constant of the measurement.

When greatest accuracy is required, heating element 9 is provided which heats the member to fluid temperature and therefore, since the fluid temperature is the arithmetic mean between object temperature and member temperature, the fluid temperature becomes exactly equal to the object temperature. The difference amplifier 14 is adapted to provide an output which is a function of the difference between half the output of 13 and the output of 12, i.e. a function of the difference between the temperatures of the fluid and the member and provides power to the heating element 9 until the difference becomes zero.

Claims

1. Device for non-contacting sensing of surface temperature of objects comprising a first temperature sensing element mounted in a protective enclosure, a member adapted to be brought in the vicinity of the object, the shape of part of the surface of the said member being such that when it is in the operating position a gap is formed between the object and said member, said member having an opening leading to the said protective enclosure, means adapted to suck the ambient fluid, usually air, from the surface of the object into the protective enclosure whereby the first temperature sensing element takes up the temperature of the inflowing fluid providing a fluid temperature signal, a second temperature sensing element adapted to sense the temperature of said member providing a member temperature signal and means to combine the signals obtained from the two temperature sensing elements in a manner that an object temperature signal is obtained which is a function of the surface temperature of the object unaffected by the temperature of the said member.

2. Device as claimed in Claim 1 in which one of the said temperature sensing elements, preferably the fluid temperature sensing element, has a positive temperature coefficient and the other temperature sensing element has a negative temperature coefficient, the two temperature sensing elements being connected in series, a signal conditioning amplifier, connecting means to connect the temperature sensing elements to the input of the signal conditioning amplifier, comprising also differentiating means to obtain a further electrical signal which is a function of the rate of change of the output of said signal conditioning amplifier and summing means to combine the said further electrical signal and the output of the signal conditioning amplifier to obtain an object temperature signal of reduced time constant.

3. Device as claimed in Claim 1 in which both said temperature sensing elements have temperature coefficients of the same sign, preferably both positive.

4. Device as claimed in Claim 3 comprising a first signal conditioning amplifier, connecting means to connect one of the said temperature sensing elements to the first signal conditioning amplifier, a second signal conditioning amplifier, connecting means to connect the other temperature sensing element to the second signal conditioning amplifier, a difference amplifier, connecting means to connect the outputs of the said two signal conditioning amplifiers to the inputs of the said difference amplifier, the output of the said difference amplifier being a function of the object temperature unaffected by the member temperature.

5. Device as claimed in Claim 4, in which the said first signal conditioning amplifier is adapted to have an output essentially proportional to twice the fluid temperature and the second signal conditioning amplifier is adapted to have an output essentially proportional to the member temperature.

6. Device as claimed in any of Claims 3, 4 and 5, comprising also differentiating means to obtain a further electric signal which is a function of the rate of change of the fluid temperature signal and means to combine the said further electric signal with the fluid temperature signal and the member temperature signal to obtain an object temperature signal of reduced time constant.

7. Device as claimed in any of Claims 1 to 5 comprising also electric heating means to heat at least that part of the member which, when in the operating position, is opposite the object, and means adapted to control the power supplied to the heating means such that the member temperature is kept equal to the fluid temperature.

8. Device as claimed in any of the preceding Claims comprising also means adapted to readout the object temperature.

9. Device essentially as described with reference to the enclosed drawings.