GB2547463A

GB2547463A - Improvements in sensor assemblies

Info

Publication number: GB2547463A
Application number: GB1602933.2A
Authority: GB
Inventors: Mollinari Maurizio; Meacock David
Original assignee: KERAFLO Ltd
Current assignee: KERAFLO Ltd
Priority date: 2016-02-19
Filing date: 2016-02-19
Publication date: 2017-08-23
Also published as: GB201602933D0

Abstract

A sensor assembly comprising a sensing device which may be in the form of a pressure transducer 12 and a housing 11 for mounting the sensing device. The sensing device is connectable to a cable 14 for conveying signals from the sensing device to a remote location outside of the housing. The sensing device is retained in the housing by means of a plug 18. The assembly further comprises at least one sealing element 20 which is deformable under pressure to provide a liquid-tight seal around the cable. The plug is designed to be engagable with the housing, or a part within the housing, to cause deformation of the sealing element. The assembly also comprises locking means 25, 27 being provided for holding the plug in position in the housing which may be an elongate pin 25.

Description

Improvements in sensor assemblies

This invention relates to sensor assemblies and in particular, though not exclusively, to assemblies for sensing pressure.

The invention provides a sensor assembly comprising a sensing device, and a housing for mounting the sensing device, with the sensing device being connectable to a cable for conveying signals therefrom to a remote location outside the housing, the sensing device being retained within the housing by means of a plug, the assembly further comprising at least one sealing element deformable under pressure to provide a liquid-tight seal around the cable, with the plug being engagable with the housing and/or a part within the housing to cause deformation of the sealing element, with locking means being provided for holding the plug in position in the housing.

By way of example, embodiments of sensor assemblies will now be described with reference to the accompanying drawings, in which:

Figure 1 is an exploded view of the component parts of one form of sensor assembly according to the invention,

Figure 2 is a cross-sectional view through the sensor assembly without the cable or sealing gland,

Figure 3 is a cross-sectional view of the finished assembly with the cable in place, and

Figure 4 is a detail view of the plug fitting in the housing.

The sensor assembly 10 seen in the drawings is for sensing pressure, and is designed to be submersible in a tank of water. The pressure measurement will be indicative of the head of water above the assembly 10 and hence indicative of the water level in the tank.

The assembly 10 comprises a generally cylindrical elongate housing 11 in which is mounted a pressure transducer 12 and a printed circuit board (PCB) 13. A cable 14 is connected to the pressure transducer 12 via the PCB 13. The cable 14 serves to convey electrical signals generated by the pressure transducer to a remote control unit outside the housing 11, typically on top of the tank. The pressure transducer 12 may be a readily available standard item.

If the tank is one that is vented, i.e. open to the surrounding atmosphere, the cable 14 also serves to connect the assembly 10 to the surrounding atmosphere via a breather tube, so that the assembly is also similarly vented. In this way, the assembly 10 is able automatically to compensate for any changes in barometric pressure (which would otherwise affect pressure readings and hence depth measurements).

The cable 14 further serves to allow the assembly 10 to be lowered into the tank for operation and raised out of it from time to time for inspection and maintenance.

Traditionally, assemblies of this nature have been made with a housing of swaged brass. In this case, however, the housing 11 can more conveniently be made of plastics material and injection moulded.

At its free end, the housing 11 contains a weight 15. This is to provide ballast to ensure that the assembly 10 will sink. The housing 11 is apertured at this end with one or more openings 16. This is to allow water in the tank into contact with the pressure transducer 12 so that it can measure the water pressure. However, it is of course vital that the PCB 13 and the electrical circuitry of the assembly 10 remain insulated from the water. Hence, the housing 11 is designed to have a watertight interior.

At the free end of the housing 11, an O-ring seal 17 around the pressure transducer 12 (normally fitted as standard) forms a watertight seal with the housing.

The cable 14 is mounted in the housing 11 via an annular plug 18. The plug 18 is insertable axially into the housing 11 (in the direction of arrow A in Figure 1) and seals against its inner bore 19 in a watertight manner via an O-ring seal 20.

To seal off the cable 14, an annular sealing gland 21 is interposed between it and a counterbore 22 in the plug 18 and a corresponding counterbore 23 in a chassis 24 which fits within the bore 19 of the housing 11 and which mounts the PCB 13. The sealing gland 21 has an axial length which is slightly in excess of the combined axial length of the counterbores 22 and 23 in which it is located. The sealing gland 21 is of a suitable resiliently flexible material such as rubber. The chassis 24 is located axially in the housing 11 by means of a shoulder 28 in the bore 19 of the housing and by a corresponding shoulder 29 on the pressure transducer 12.

Axial pressure applied to the plug 18 in its direction of insertion into the housing 11 (arrow A) will cause compression of the sealing gland 21. The axial clamping action on the sealing gland 21 will have the effect of deforming it so that it expands laterally into tight contact with both the cable 14 and the counterbores 22, 23, thus creating a watertight seal around the cable. With the O-ring seal 20 sealing the plug 18 against the bore 19 of the housing 11, the PCB 13 and the electrical connections between it, the pressure transducer 12 and the cable 14 in the interior of the housing are thus effectively sealed off from the water in the tank.

It will be understood that the various component parts of the assembly 10 are dimensioned so as to allow sufficient axial movement of the plug 18 within the housing 11 to cause the intended deformation of the sealing gland 21 to effect a watertight seal. In practice, this will typically involve compression of the sealing gland 21 by about 10% of its axial length.

The plug 18 is designed to be held in its sealing position by means of a locking mechanism, in this case pair of parallel pins 25. These pins 25 are arranged to be engagable with the housing 11 in a direction transverse to its longitudinal axis (as illustrated by arrow B in Figure 1). As seen in Figure 4, two pairs of aligned holes 26 are formed through the housing 11 to receive respective pins 25. Similarly, holes 27 are formed transversely through the plug 18 for receipt of the pins 25. At rest, i.e. before deformation of the sealing gland 21, the holes 27 in the plug 18 will not align with the holes 26 in the housing 11. However, once sufficient axial pressure has been applied to the plug 18 to compress the sealing gland 21, the respective holes 26, 27 will come into alignment. The pins 25 are inserted at this stage to hold the plug 18 in its sealing position and hence render the interior of the housing 11 watertight.

To ensure correct alignment of the holes 26 and 27 for receipt of the pins 25 during manufacture, the plug 18 is conveniently keyed to the housing 11 - illustrated by reference numeral 30 in Figure 4.

The pins 25 also perform another function. They are arranged to be spaced apart by a distance x (as seen in Figure 4) that is slightly less than the outer diameter of the cable 14. Thus, when the pins 25 have been inserted into the housing 11 and the plug 14 in the manner described above, they will straddle the cable 14 with an interference fit. This is useful, because it will help to prevent the cable 14 from detaching from the housing 11 and thus retain the integrity of the assembly 10 in use.

It will be understood that the locking mechanism for holding the plug in position in the housing may take different forms. For example, instead of using pins, the mechanism could alternatively comprise a circlip or the like fitted into a groove in the bore of the housing.

The sensor assemblies described above have the advantage of being relatively simple to manufacture in terms of process, materials and cost. They have the further advantage that they are capable of disassembly and re-assembly, eg for maintenance purposes.

Claims

1. A sensor assembly comprising a sensing device, and a housing for mounting the sensing device, with the sensing device being connectable to a cable for conveying signals therefrom to a remote location outside the housing, the sensing device being retained within the housing by means of a plug, the assembly further comprising at least one sealing element deformable under pressure to provide a liquid-tight seal around the cable, with the plug being engagable with the housing and/or a part within the housing to cause deformation of the sealing element, with locking means being provided for holding the plug in position in the housing.

2. An assembly as claimed in claim 1 wherein the housing is elongate and the plug is insertable into the housing in the direction of its longitudinal axis.

3. An assembly as claimed in claim 2 wherein the locking means is operable in a direction transverse to said longitudinal axis.

4. An assembly as claimed in claim 3 wherein the at least one sealing element is deformable under pressure applied in the direction of the longitudinal axis.

5. An assembly as claimed in claim 4 wherein the locking means comprises at least one elongate pin engagable by both the plug and the housing.

6. An assembly as claimed in claim 5 wherein both the plug and the housing have holes to receive the at least one pin, with the holes being arranged to be aligned when the sealing element is under deformation.

7. An assembly as claimed in claim 5 or claim 6 wherein the locking means comprises two elongate pins spaced apart with their longitudinal axes parallel.

8. An assembly as claimed in claim 7 wherein the spacing of the pins is arranged to be less than the diameter of the cable, with the pins being arranged to straddle the cable in use and grip it with an interference fit, thereby helping to prevent its detachment from the housing.

9. An assembly as claimed in any preceding claim wherein the plug and housing are keyed together so as to remain in the same rotational orientation with respect to each other.

10. An assembly as claimed in any preceding claim wherein the at least one sealing element is an annular body of resiliently flexible material.

11. An assembly as claimed in any preceding claim wherein the housing is made of plastics material.

12. A sensor assembly substantially as herein described with reference to the accompanying drawings.