GB2182775A - Pressure and temperature sensing device - Google Patents

Abstract

The device mounted in the wall (13) of a liquid filled tank comprises in a single unit a temperature sensor and a pressure sensor whereby only one hole is required in the tank wall. The pressure sensor comprises a head (5) for immersion in the liquid in the tank and a shank (3) which leads out of the tank to information processing equipment. The temperature sensor is in the form of a probe which is fitted in a keyway (25) in the shank (3) with its probe end in a hole (24) bored in the head (5). Thus the probe takes the temperature of the liquid indirectly by measuring the temperature of the head (5) which is in contact with the liquid. <IMAGE>

Description

SPECIFICATION Tank data retrieval device The present invention relates to the retrieval of data in the form of pressure and temperature readings from a tank containing fluid, more usually liquid.

In order to obtain this data at the present time it is necessary to take separate temperature and pressure readings. From a series of pressure readings at different levels it is possible to calculate the depth and specific gravity of the contents of the tank. The equipment that is used is either a series of pitot tubes for the pressure readings, immersed in the tank contents up to different depths, or a series of pressure transmitters mounted in specially cut-out apertures in the tanks. The temperature readings are made either by suspending a temperature probe into the liquid from above, or by forming one or more further holes in the side of the tank through which respective temperature probes are mounted. In addition to the extra work involved in preparing the additional holes, the holes have also to be effectively sealed.

According to the present invention there is provided a tank data retrieval device comprising a single unit adapted to have at least one end immersed in the fluid in the tank, the said unit housing a pressure sensing device and a temeprature sensing device.

Preferably the unit is a pressure transmitter having a chamber partially defined by a moveable surface, the other side of which surface is in contact with the fluid in use of the device, means to equalise the pressure in the chamber with that of the said fluid at the point of contact wherebn a reading of chamber pressure is indicative of the pressure of the fluid at that level, the pressure transmitter being arranged to receive a temperature probe housed therein with the temperature sensing end of the probe being indirectly in contact with the fluid.

Advantagelusly the transmitter includes a head having a member in direct contact with the fluid in the tank in use of the device and a shank attached to the head which shank protrudes through the tank wall; the member being bored to receive a temperature probe which is fitted therein via a key-way in the shank.

The present invention will now be described, by way of example with reference to the accompanying drawings which is a longitudinal cross-section through a device according to the invention.

Referring to the drawing, there is shown a data retrieval device in the form of a transmitter which is slightly mushroom shaped having a head 1 and a stem 2. The stem, which is generally cylindrical, comprises a shank 3 which is an open ended tube having an inner diameter of 6mm counterbored to 7mm for about two-thirds of its length.

A generally cylindrical spindle 4 is mounted into the shank 3 with its nose 5 protruding from the tube 3 at the mushroom head end 1 of the shank 3. The spindle is formed from a 6mm diameter tube into one end of which the nose piece 5 is blazed. The nose piece 5 comprises a convex end 5a which protrudes from the shank 3, which end 5a has a passage 6 therethrough forming a bleed nozzle leading from outside the nose 5 to the inside of the tube 4. A tubular part 5b of the nose piece 5 fits into the tube end 4 and is blased thereto with a flange of the end 5a abutting the end of the tube 4. Remote from the nose 5, the tube 4 fits the shank bore exactly for a length of about three to four times the diameter of the tube.With the use of a suitable sealant between the contacting surfaces no further sealing is required at this end of the stem to prevent seepage between the contacting surfaces. Where the shank 3 is couterbored an annular space 7 is formed between the shank and the spindle 4, which forms part of a chamber 8.

A grub screw 9 is located in a screw threaded hole 10 in the shank 3 and may be tightened on to the spindle when the required position of the spindle 4 in the shank 3 has been achieved. Access to the chamber 8 is given through two screw threaded apertures 11 in the shank, only one of which is illustrated. Although the apertures 11 are shown as screw threaded, any method of pipe connection can be used. One aperture 11 forms the inlet for air under pressure to the chamber 8 and will be connected to an air compressor (not shown). The other aperture is connected to a pressure reading device for reading the pressure at any time existing in the chamber, particularly an equilibrium pressure.

The head of the transmitter comprises a mount 12 to which the shank is fixed, the shank having a narrower diameter end 3a to which the mount 12 is welded. The mount 12 is generally cylindrical having a larger diameter portion which bears against a tank wall 13 via a rubber washer 14, and a smaller diameter portion. A valve member 15 encloses a space 16 bounded also by the front end of the mount 12 which space is in flow communication with the space 7 and these spaces together form the chamber 8. The valve member 15 is stainless steel and comprises a circular wall or disc 17. The disc 17 is permanentally fixed throughout its circumference to a bellows section which is a section of convolutions cut from a length of steel bellows. The disc is of thicker material than the bellows material and is substantially inflexible under the conditions of use.The other end of the bellows section 18 is welded to the mount 12.

The bleed nozzle 6 in the nose 5 acts as the outlet of the chamber 8. The bleed nozzle leads directly into a wider diameter cylindrical channel 19 which extends along the length of the spindle tube 4 and exhausts to the atmosphere at the rear end of the spindle. The spindle 4 extends outside the shank 3 and this portion is chamferred to provide flats suitable for receiving a spanner to enable the spindle to be rotated or held in the shank.

To assemble the transmitter the spindle is moved into the shank until it touches the wall exerting no force on either component. The spindle is then locked in position by tightening the grub screw 9 against the spindle 4. The relaxed position of the wall 17 substantially blocks the bleed nozzle 6. The wall can move transversely off the bleed nozzle in the event of an incrase in pressure in the chamber 8 due to the continuing supply of gas under pressure from the inlet 11. The natural resilience in the bellows section of the valve member 15 enables the wall 1 7 to move back to the nose automatically as a result of a pressure drop occuring across the wall between the tank and the chamber 8.

The transmitter is mounted through an aperture in a tank 13 with the head inside the tank and most of the shank, including particularly the chamber inlet and chamber reading access outside the tank. A rubber washer 14 is fitted between the mount 12 and the tank wall 13 to seal the transmitter to the tank and a lock nut 21 tightens against the outside of the tank optionally through a second washer 22, by travel along the screw threaded outer portion 23 of the shank.

The operation of the pressure sensing aspect of the transmitter is as follows: air under pressure is supplied to the chamber 8 through the inlet port 11. If the pressure in the tank 13 is greater than that in the chamber 8 the wall 17 will substantially block off the outlet 6 so that a build up of pressure occurs in the chamber. When there is an equilibrium between the pressure in the tank 13 and in the chamber 8, the wall 1 7 is pushed away from the nose 5, unblocking the outlet 6 so that excess air can leave the chamber, thus maintaining in the chamber a fairly constant pressure which is equal to that in the tank. This pressure can be measured via the other port 11 by conventional means.

By virtue of its permanent contact with the liquid in the tank when the device is in use, the mount 12 will be at substantially the same temperature as the liquid. The effect of the flow of gas in the chamber 8 will not substantially effect this. Therefore by taking the temperature of the mount for the liquid temperature reasonable accuracy is assured. To make this possible the mount 12 is bored at 24.

The shank 3 is milled at 25, including the screw threaded section, to provide a keyway for a temperature probe 26, the thermocouple end of which is inserted into the bore 24. To prevent the temperature probe from falling out of the key-way during assembley or use the probe is bound into the keyway, for example by a length of wire wrapped round the shank.

By incorporating the temperature sensing in the same unit as the pressure sensing the number of data retrieval holes that need to be made in the tank is reduced by at least one. If the temperature probe is included in each pressure transmitter more information is retrieved than is presently the case. The added information of temperature levels at different levels in the tank may indicate a need for stirring.

Claims (5)

1. A tank data retrival device comprising a singie unit adapted to have at least one end immersed in fluid in the tank, the said unit housing a pressure sensing device and a temperature sensing device.

2. A device according to claim 1 wherein the temperature sensing device senses the temperature of the fluid indirectly.

3. A device according to claim 1 or 2 wherein the unit is a pressure transmitter having a head for immersion in the fluid and arranged to receive a temperature probe housed therein, with the temperature sensing head of the probe adapted to sense the temperature of the head of the unit.

4. A device according to claim 3 wherein the transmitter includes a shank attahced to the head, which shank protrudes through the tank wall, the head being bored to receive a temperature probe, which probe is fitted therein via a keyway in the shank.

5. A tank data retrieval device substantially as herein described with reference to the accompanying drawing.