GB2212668A - Circuit housings - Google Patents

Abstract

A circuit housing, for a probe (18) for a fluid vessel, has a hollow body (2) and a cap (1). The probe (18) is attached to the base of the body and connector wires (19) from the probe pass up through the body (2) and the cap (1) to be secured to terminals (5) recessed into the exterior of the cap. A printed circuit board (20), profiled to match the interior of the body (2), fits into the latter and connections from that board to the terminals (5) pass up through the cap and are similar within the recesses. The probe contains a thermocouple or resistance thermometer. <IMAGE>

Description

"Improvements relating to Electric and Electronic Components" This invention relates to electric and electronic component housings, and is particularly concerned with housing for circuitry associated with thermocouples and resistance thermometers.

Such a housing is usually mounted externally of a vessel whose contents are to be monitored, and a probe extends from it through the wall of the vessel, there being appropriate sealing and safety measures interposed.

The response from the probe is translated into one or more signals by the electric and electronic components in the housing and these signals are transmitted on to operate warning and indicator devices for example.

Such an assembly as a whole is known and will be referred to in this Specification as a transmitter.

It is important to have a housing to which access is easy and which, when assembled, is safe.

According to the present invention there is provided a transmitter housing comprising a hollow body and a closure cap therefor, the hollow body being adapted to receive a printed circuit board (PCB) and to have a probe extending therefrom on the opposite side from the cap, and the cap having recesses in its outer face in the bases of which there are terminals, connections from the probe to the terminals being led through the body and the cap for external attachment, but within the recesses.

Connections from the PCB to the terminals will preferably be led through the cap for external attachment to those terminals within the recesses.

Conveniently, the terminals include screw members adjustable between setting-up positions partially proud of the cap, (where connecting wires can be wrapped round) and securing positions wholly below the mouths of the recesses and inaccessible by hand.

Preferably, the PCB will be generally parallel to the cap and be profiled closely to correspond to the interior of said body.

The housing may be generally cylindrical, in which case the probe will be substantially co-axial therewith. It may then have a hollow co-axial column through which the connections from the probe to the terminals are led, the PCB being apertured to fit around the column.

The probe is conveniently attached by a plate secured to the underside of the body, and the cap and body may then have aligned apertures registering with smaller apertures in the plate. These will receive mounting bolts with springs surrounding the bolt shanks and acting between the plate and the bolt heads within the aligned apertures.

Some cap recesses and terminals may serve for connection of an external power supply, and conveniently the output signals from the PCB are superimposed on the power supply. The cap may also be apertured for the adjustment of a component on the PCB within the housing, and preferably the PCB will be encapsulated by material injected through the cap after assembly.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of the cap of a transmitter housing, Figure 2 is a plan view of the main body of the transmitter housing with the cap removed, Figure 3 is a vertical section, to an enlarged scale, through the housing, on the lines III-III of Figures 1 and 2 combined, Figure 4 shows both sides of a PCB for mounting within the housing, and Figure 5 is a circuit diagram associated with the PCB.

The housing is a generally cylindrical twopart moulded plastics construction with a flat on one side, both in the cap 1 and the main body 2.

It will itself-be housed in an outer shell or head (not shown) which does not form part of this invention.

The cap 1 has recesses in its upper, outer face, a central one 3 extending from near the flat diametrically across the cap and splitting into three fingers 4 on the opposite side. Inset into the base of each of these fingers there is a terminal 5 comprising an internally screw-threaded sleeve 5a which receives a screw 5b, and adjacent each of these terminals is a narrow through passage 6 just large enough for an insulated, single core signal wire 7 to be threaded through. Above these passages they will generally be secured to tabs or washers through which the screws 5b will pass to clamp them.

On either side of the recess 3 there are two keyhole shaped recesses 8 diverging from the flat, to which they are open, and in the base of the-circular portion of each of these recesses there is a hexagonal hole 9 to locate a correspondingly shaped nut (not shown) which receives a terminal screw (also not shown) for power supply connection. The power supply wires, which will also be arranged to carry the output signals superimposed on the supply voltage, will be from an external source and be led through the shell or head into a space created by the flat.

Also on either side of the recess 3, on the diameter transverse to the section line III-III, there are holes 10, and between each of them and the nearest finger 4 another, smaller hole 11.

Within the recess 3 there is a central aperture 12, and, near the flat, a further hole 13.

The body 2 is hollow and has a central upstanding hollow column 14, which registers with the aperture 12. On either side of this there are hollow bosses 15 against the inside of the cylindrical wall, their through passages registering with, and being of the same diameter as, the holes 10. On the base there are two thickened portions 16 drilled into from the underside and used for securing to a mounting plate 17 at the head of a probe 18 which extends co-axially away from the housing. Wiring 19 from within the probe is led through the column 14 and the aperture 12 to the terminals 5 within the finger recesses 4.

The screws 5b are sufficiently long to be still engaged with sleeves 5a when their heads are proud of the cap 1. This makes placement of the wires 7 and the probe wiring 19 simple; but when they are fully screwed down to clamp those wires the screw heads are well down below the mouths of the recesses 4 and are not accessible by finger. The same applies to the power supply terminals in the recesses 8.

The complete terminal assembly therefore forms an enclosure with a degree of protection to "I.P.20" without any need for additional covers.

The body 2 receives a printed circuit board (PCB) 20 shaped to fit closely within it and to lie parallel to the cap I as seen from Figures 2, 3 and 4.

The wire connections 7 lead from the PCB 20 and there will be further wires (not shown) to the power supply which is brought to the terminals within the recesses 8. Two variable resistors on the PCB 20 can be adjusted by a screwdriver through the small holes 11. Clearance and creepage distances from any terminal to any earthed part are sufficient fully to comply with the requirements of B.S.5501 Pt. 7 (Intrinsic Safety "i"), and after assembly the PCB 20 is encapsulated by injecting suitable setting material through the hole 13. The adjustment screws for the variable resistors will, however, remain exposed within the lower ends of the holes 11.

The mounting plate 17, and thus the housing itself, is resiliently mounted in the shell or head.

Bolts within the hollow bosses 15 and accessible through the holes 10 screw into the head through smaller holes in the plate 17, and springs surrounding the shanks of the bolts act between the bolt heads and the plate.

Figure 5 shows an example of a circuit diagram of the PCB.

Claims (13)

1. A transmitter housing comprising a hollow body and a closure cap therefor, the hollow body being adapted to receive a printed circuit board (PCB) and to have a probe extending therefrom on the opposite side from the cap, and the cap having recesses in its outer face in the bases of which there are terminals, connection from the probe to the terminals being led through the body and the cap for external attachment, but within the recesses.

2. A housing as claimed in claim 1, wherein connections from the PCB to the terminals are led through the cap for external attachment to those terj#ina'..s within the recesses.

3. A housing as claimed in claim 1 or 2, wherein the terminals include screw members adjustable between setting-up positions partially proud of the cap and securing positions wholly below the mouths of the recesses.

4. A housing as claimed in claim 1, 2 or 3, wherein the PCB lies generally parallel to the cap and is profiled closely to correspond to the interior of the said body.

5. A housing as claimed in any preceding claim, wherein the housing is generally #cylindrical and the probe is substantially co-axial therewith.

6. A housing as claimed in claim 5, wherein the body has a hollow co-axial column through which the connections from the probe to the terminals are led, the PCB being apertured to fit around the column.

7. A housing as claimed in any preceding claim, wherein the probe is attached by a plate secured to the underside of the body.

8. A housing as claimed in claim 7, wherein the cap and body have aligned apertures registering with smaller apertures in the plate, these receiving mounting bolts with springs surrounding the bolt shanks and acting between the plate and the bolt heads within the aligned apertures.

9. A housing as claimed in any preceding claim, wherein some cap recesses and terminals are for the connection of an external power supply.

10. A housing as claimed in claim 9, wherein the output signals from the PCB are superimposed on the power supply.

11. A housing as claimed in any preceding claim, wherein the cap is apertured for the adjustment of a component on the PCB within the housing.

12. A housing as claimed in any preceding claim, wherein the PCB is encapsulated by material injected through the cap after assembly.

13. A transmitter housing substantially as hereinbefore described with reference to the accompanying drawings.