GB2215839A - A temperature sensor calibration device - Google Patents

Abstract

A temperature sensor calibration device e.g. for thermo couples comprises an elongate quartz casing 18 which sealingly surrounds a generally cylindrical tube 16. A freezing or melting point cell is positioned in a cavity 20 between the tube 16 and the casing 18. The tube 16 is open at both ends so that an elongate probe having a plurality of sensors thereon can be passed through the tube 16 and positioned at any desired location therealong. The device enables absolute calibration of any of the sensors positioned along the probe. <IMAGE>

Description

A TemPerature Sensor Calibration Device The present invention relates to temperature calibration in general and a device for calibration of an elongate multi-sensor probe in particular.

In some manufacturing processes, such as the fabrication of semiconductor substrates, it is required that use is made of a furnace which has a very specific temperature profile. In order to enable the required temperature profile to be established and maintained, special thermocouple probes have been developed. These probes typically comprise between 3 and 9 thermocouples strategically located along the length of the probe.

Difficulty arises in the calibration of such probes.

Conventional thermocouple calibration devices, for example using melting point or freezing point cells, comprise a hollow cylindrical receptacle open at one end. The probe is inserted into the receptacle through the open end, the other end being closed. A conventional calibration device of this type can only be used to calibrate the thermocouple(s) located adjacent the tip of the above described probe..

One device which would enable calibration of the probe involves a collar shaped bath provided with a standard thermocouple. The probe is passed through the collar until the thermocouple to be calibrated is adjacent the standard thermocouple. The temperature of the bath is raised until the required temperature is monitored by the standard thermocouple and the thermocouple of the probe is calibrated by comparison against the standard. However, this method of calibration and the calibration device used can be improved upon.

According to one aspect of the present invention there is provided a temperature sensor calibration device comprising a casing with a sensor receiving aperture passing therethrough, the casing housing a melting or freezing point cell.

According to a second aspect of the present invention there is provided a method of calibrating temperature sensors housed in an elongate probe, comprising the steps of: providing a calibration device having a casing with a sensor receiving aperture passing therethrough and housing a melting or freezing point cell; and providing relative movement between the probe and calibration device such that each sensor within the probe may be calibrated.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings. in which: Figure 1 is a diagrammatic cross-sectional view of a calibration device according to one embodiment of the invention; Figure 2 is a diagrammatic cross-sectional view of the main casing of the device illustrated in Figure 1; and Figure 3 is a diagrammatic cross-sectional view of the two portions (separated) of the insert received in the main casing illustrated in Figure 2.

A calibration device embodying the present invention is illustrated in Figure 1 and the main components thereof are shown in more detail in Figures 2 and 3. As illustrated, the calibration device 10 comprises a main casing 12 in which a freezing point cell 14 is positioned.

The main casing 12 is formed of quartz. As best seen in Figure 2, casing 12 comprises two concentric hollow tubes, 16 and 18. The annular space 20 between the tubes is closed at one end by a shoulder 22 in the outer tube 18 which is sealed against the outer surface of tube 16. A cap 24 is used to close the other end of annular space 20. An evacuation port 26 is provided in cap 24, which enables the annular space 20 to be evacuated once the device is assembled and cap 24 sealed with tubes 16 and 18.

As shown in Figure 1, a freezing point cell 14 is housed within casing 12. Ceramic wool 28 is used as packing within annular space 20. This provides thermal insulation and positional stability for the freezing point cell.

The freezing point cell comprises two components, which are shown separate from each other in Figure 3.

These components are an outer sheath 30 and an inner sheath 32. The inner sheath 32 is configured to be a push fit within the outer sheath 30 and in this embodiment both sheaths are formed of graphite. When assembled, the two sheaths are held relative to each other by graphite pegs (not shown) which extend through radial apertures 34, provided in both sheaths. Inner sheath 32 is dimensioned for push fit retention on tube 16 of casing 12, within annular space 20. The outer surface of sheath 30 is spaced apart from tube 18 and the gap therebetween filled by the ceramic wool 28.

Operation of the freezing point cell 14 is conventional and therefore will not be described herein.

The above described calibration device can be slid along the multi-sensor probe so as to enable precise calibration of the relevant sensor(s) regardless of their position along the length of the probe. It will be appreciated that this arrangement provides absolute calibration of the sensors, in contrast to the use of a standard thermocouple. Of course, the device is not limited to the use of a graphite freezing point cell or even to freezing point cells in general. Casing 12 could equally well house a melting point cell. More than one calibration device, i.e. each having different cells therein, could be used in the calibration of an elongate multi-sensor probe.

As will be redily apparent to those skilled in the art, various modifications can be made to the above described embodiment without departing from the scope of the present invention.

Claims (10)

1. A temperature sensor calibration device for enabling absolute calibration of temperature sensors, the device comprising a casing with a sensor receiving aperture passing therethrough, the casing housing a melting or freezing point cell.

2. A device according to claim 1, wherein the aperture passing through the casing is elongate and open at both ends thereby enabling an elongate probe to be passed therethrough such that any one of a plurality of sensors positioned along the probe can be positioned within the aperture.

3. A device according to claim 2, wherein the elongate aperture is defined by a generally cylindrical tube positioned within the casing such that at least part of the length of the tube is surrounded by the melting or freezing point cell.

4. A device according to claim 3, wherein a cavity is defined between the casing and tube, which cavity houses the melting or freezing point cell and comprises a ceramic wool packing for providing thermal insulation and positional stabililty for the melting or freezing point cell.

5. A device according to claim 4, wherein the cavity comprises an evacuation port for enabling evacuation of the cavity.

6. A device according to any preceding claim wherein the aperture is of sufficient length for a plurality of sensors along the probe to be simultaneously positioned therein.

7. A device according to any one of the preceding claims, wherein the casing is made of quartz.

8. A device according to any one of the preceding claims arranged for calibrating the sensors of a probe, which probe is intended for measuring the temperature profile of a furnace.

9. A method of calibrating temperature sensors housed along an elongate probe, comprising passing the probe through an aperture of a device according to any one of the preceding claims so that the sensor to be calibrated is positioned within the aperture.

10. A temperature sensor calibration device substantially as herein described with reference to Figures 1 to 3 of the accompanying drawings.