GB2114293A

GB2114293A - Equipment for calibration of instruments having a temperature sensing unit

Info

Publication number: GB2114293A
Application number: GB08301081A
Authority: GB
Inventors: Jens Schmidt Hansen
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-01-25
Filing date: 1983-01-14
Publication date: 1983-08-17
Also published as: DE3301627A1; GB8301081D0; DK147009C; DK31482A; DE3301627C2; JPS58129335A; DK147009B; GB2114293B

Abstract

An equipment for calibration of instruments having a temperature sensing unit (2) comprises a chamber or a pocket (7) for insertion and receiving the sensing unit (2), and means for adjusting and generating a desired temperature in the chamber or pocket. Furthermore, the equipment comprises means (6) for sensing the actual temperature in the chamber (7). In order to provide a calibration equipment, which is capable of being quickly re-set from one desired temperature to another, the chamber (7) comprises a HF-coil (4), the axis thereof being positioned centrally in the chamber (7), and said coil is connected with an adjustable HF-generator. <IMAGE>

Description

SPECIFICATION Equipment for calibration of instruments having a temperature sensing unit The present invention relates to equipment for calibration of instruments having a temperature sensing unit, said equipment comprising a chamber or a pocket for insertion and receiving the sensing unit, means for adjusting and generating a desired temperature in the chamber or pocket, and means for sensing the acutal temperature in the chamber or pocket.

In connection with many types of process surveying or process controlling there is a demand for temperature measuring or temperature registrating instruments, such as thermometers and temperature recorders, and temperature controlled instruments, such as thermostates. It is common to such instruments that a temperature is to be measured and sensed in a definite and often not very accessible place, and for this purpose a signalling temperature sensing unit is used, mounted in a suitable holder or probe which may be inserted and located so that the sensing unit is in the desired place. The signal from the sensing unit or sensor is applied e.g.

to a an indicating or registrating instrument or to other signal treating equipment. For instance in power plants or in engine rooms on ships such instruments are used to a wide extent, and it may often have serious consequences, if the instrument does not operate in a reliable and correct manner. Therefore, it is required that the instruments are calibrated precisely before taken into use and, besides, the operational conditions may necessitate that the instruments are checked and re-adjusted at regular intervals.

For this purpose different types of portable calibration equipment have been developed capable of generating and maintaining various well-defined temperatures in a chamber or a pocket in which the temperature sensing unit of an instrument may easily be inserted after having been removed from is usual place of use.

A type of calibration equipment is known based on a metal core defining a chamber or a pocket and which is provided with built-in electric heating elements. By means of controlling equipment comprising a thermosensor in the chamber, a desired temperature may be generated in the chamber, and e.g. the pointer or scale of a thermometer may then be controlled and adjusted as needed, when its sensing unit is in the chamber and thus is exposed to the adjusted temperature.

Actually, such a metal core functions very well, but still has the disadvantage that a certain period of time is required to stabilize the chamber temperature at a desired, adjusted value, and in particular when an instrument is to be calibrated in a number of succeeding scale points, the thermal inertia of the metal core causes the calibration operation to be time consuming. In particular when the core temperature is to be re-set from a higher to a lower value a cooling blower is used in order to accelerate a temperature decrease in the core, the blower being built into the calibration equipment.

Besides, core materials have been used, such as alumina and copper, of good heat conductivity, but such metals have the tendency to glow or oxide at higher temperatures in the area of 500-600"C. On the other hand, a metal, such as stainless steel, which may resist these high temperatures, has a considerably poorer heat conductivity and is consequently not quite suited, either.

The calibration equipment of the invention is characterized in that the chamber or pocket comprises or is surrounded by a HF-coil, the axis thereof being positioned centrally in the chamber or pocket, and preferably being coincident with a logitudinal axis of the chamber or pocket, and in that the coil is connected with an adjustable HF-generator.

Hereby, the metal core hitherto used having electric heating elements is completely eliminated and replaced by a heating means which is much faster, both when the temperature in the chamber is to be stabilized at a new, higher value, and when the temperature in the chamber is to be decreased. Besides, the equipment according to the invention is substantially lighter than calibration equipment with metal core, which is of importance in portable units, and the power consumption is minimal. Finally, the equipment of the invention is well suited for high temperatures, and the demand of the equipment for inspection and maintenance is considerably less than in known equipments with metal core and electric heating elements.

In the following, the invention will be described with reference to the drawing, wherein Figure 1 schematically shows a longitudinal section through a portion of an embodiment of the calibration equipment according to the invention, and Figure 2 is a schematical diagram for illustrating the function of the equipment according to the invention.

In Fig. 1 of the drawing a schematically shown thermo sensing unit is seen, comprising a housing 2 of metal. The thermo sensing unit shown is of a mercury type having a capillary tube 1 leading to a registrating instrument (not shown). Other types of thermo sensors may, however, also be suitable.

The housing 2 is inserted into a chamber or a pocket 7 defined within a HF-coil 4 and may be filled with gas or liquid.

A precision thermo sensor 6 is located in a suitable retainer which, preferably, may be displaced into the chamber 7 for contact with the active portion 5 of the housing. The precision thermo sensor 6 may, alternatively, be positioned centrally in the chamber 7, so that the free end of the thermo sensor housing 2 may be brought into touch and good thermical contact with the thermo sensor 6.

When the metal sensor housing 2 is inserted into the chamber 7, and when the coil 4 is provided with high frequency power, the field generated by the coil causes a heating of the thermo sensor housing 2, and the precision thermo sensor 6 reads the actual temperature value obtained.

As shown schematically in Fig. 2, the coil 4 is connected with an adjustable HF-generator C which is controlled in dependency of a desired temperature value, adjustable at A, and the actual temperature value, which may be sensed by the precision thermo sensor 6.

When the actual temperature value shown at F, if desired, is coinciding with the adjusted temperature value desired, the instrument belonging to or associated with the thermo sensor housing 2 may be calibrated or re-adjusted onto the temperature in question.

In Fig. 2, the generator C is controlled by a differential amplifier B, one input thereof receiving the desired temperature value signal from A, while the other input receives the actual temperature value signal from the thermo sensor 6 in the chamber 7.

As indicated in Fig. 1, the coil 4 may appropriately surround a thermo insulating non-metallic material 3, defining the chamber or pocket 7. Thereby, it is easier to obtain a uniform temperature in the chamber 7.

As already mentioned, the precision thermo sensor 6 may also be located centrally in the bottom of the chamber or pocket 7 and, if so, a socket for receiving the free end of the sensor housing 2 may be provided.

With a principle as that shown in Fig. 2, the acutal temperature of the chamber may quickly be brought to coincide with the desired temperature adjusted, and a number of subsequent calibrations or adjustments may be performed rather quickly, since the quantity of material, the temperature of which is to be changed by the transition from a desired temperature to the next one, is considerably less than in known equipment having a metal core.

If desired, the chamber 7 may, however, also comprise a suitable metal core, e.g. of temperature-resistent stainless steel, since HFheating in itself gives rise to a more uniform heating.

Furthermore, the thermo sensor 6 may be mounted on a clip arranged to be applied on the sensor housing 2 and thereby creating good thermal contact between the housing 2 and the thermo sensor 6.

Further variations from the embodiments illustrated in the drawing and described above may be resorted to without departing from the spirit of this invention, and the scope of the invention should be determined only as limited by a proper interpretation of the terms used in the following claims.

Claims

1. An equipment for calibration of instruments having a temperature sensing unit, said equipment comprising a chamber or a pocket for insertion and receiving the sensing unit, means for adjusting and generating a desired temperature in the chamber or pocket, and means for sensing the actual temperature in the chamber or pocket, CHARACTERIZED in that the chamber or pocket comprises or is surrounded by a HF-coil, the axis thereof being positioned centrally in the chamber or pocket, and preferably being coincident with a longitudinal axis of the chamber or pocket, and in that the coil is connected with an adjustable HF-generator.

2. The equipment of claim 1, CHARAC TERIZED in that the generator is controlled by the output signal from a differential amplifier, one input thereof being connected with said means for adjusting the desired temperature value, and the other input thereof being connected with said means for sensing the actual temperature value.

3. The equipment of claim 1 or 2, CHAR ACTERIZED in that the coil surrounds or is incorporated in a thermo insulating material defining said chamber or pocket.

4. Equipment for calibration of instruments having a temperature sensing unit substantially as hereinbefore described with reference to and as illustrated in Fig. 1 or in Fig. 2 of the accompanying drawings.