GB1571754A - Thermal switch - Google Patents

Description

(54) THERMAL SWITCH (71) We, STANDARD TELE PHONES AND CABLES LIMITED, a British Company of 190 Strand, London W.C.2., England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to thermal switches, i.e. to switches which respond when the tern- perature to which they are subjected reaches or exceeds a preset level.

Many conventional switches for the above purpose rely on the use of hi-metallic strips, which tend to inaccuracy, especially as they age. Also they tend to be relatively costly.

Hence an object of this invention is to provide a thermal switch which is relatively cheap and simple, and has good accuracy.

According to the invention there is provided a thermal switch which includes a sealed enclosure containing a liquid halocarbon, one wall of the enclosure being a bowed disc, wherein when the temperature to which the switch is subjected passes through a preset value the fluid pressure within the enclosure changes in such a way as to cause the bowed disc to change from a concave state to a convex state or vice-versa, and wherein the change of state of the bowed disc causes a switching operation on electrical contacts forming part of the switch.

Embodiments of the invention will now be described with reference to the accompanying drawings, which show schematically a number of embodiments of the present invention, the embodiments being shown sectionalised.

The switch shown in section in Fig. 1 has a cylindrical capsule 1 containing a volatile liquid such as dichlorodifluoro methane (CC12F2), sold as FREON (Registered Trade Mark), the lower side of the capsule being a thin metallic disc 2, which is bowed inwardly.

This capsule is mounted in a suitable electrically insulating material member 3.

This disc 2 has on its outer face a pillar 4 which is in driving relation with the centre portion of a slotted metallic disc 5. The rim of this disc is secured as shown to the structure of the switch.

Below the disc 5, but out of contact therewith there is a further metallic disc 6, such as a Belleville washer, whose rim is secured to the structure of the switch. There are two electrical contacts heaving pins 7 and 8 for connection to an electrical unit. The first contact is formed by the disc 5, which is electrically connected to the pin 8 via the portion 9, while the second contact is formed by the disc 6, which is electrically connected to the pin 7.

When the temperature reaches the level to which the switch is set, vapour pressure in the enclosure flips the bowed disc 2 from its concave to its convex state, which causes the piller 4 to drive the central portion of the slotted disc 5 into engagement with the disc 6, thus completingthe electrical circuit.

The switch shown in section in Fig. 2 is similar in many respects to that of Fig. 1, but provides a break contact. Hence only the elements which differ from Fig. 1 will be described. The slotted disc 10 which is driven by the capsule 1 is not directly connected to either of the terminal pins 7 and 8. However, its central portion bridges two metallic cont tact members 11 and 12 which are connected respectively to the pins 8 and 7. Hence it will be seen the contacts of the switch are normally closed.

When the temperature reaches the level at which the switch is intended to operate, the disc 2 drives the disc 10 down, so that the connection between the members 11 and 12 is broken.

In both of the switches described above, when the temperature falls below the preset level, condensation of the vapour causes the bowed disc 2 to revert to its condition shown in the drawings.

A change-over switch can be made by producing what is in effect a combination of Figs. 1 and 2. Such a switch would be like Fig. 2, but with a connection to the disc 10 and a disc such as the disc 6 below the disc 10, also with an electrical connection to it.

By suitably coupling these connections we produce a change-over.

Fig. 3 shows a variant of the switch of Fig. 1 in which the disc 2 moves against a resetting spring 15 held in place in the structure by a set screw 16, which is adjustable to vary the effect of the spring on the disc 2.

Thus when the preset temperature is reached the disc 2 flips over to engage a Belleville washer 17, the disc 2 and Belleville washer 17 being connected respectively to the terminal pins 18 and 19.

Fig. 4 shows in highly schematic form how a switch such as described above can be rendered adjustable by the use of a heater 20 in the capsule: this preheats the filling to an adjustable level as decided by the variable resistor 21.

Fig. 5 shows a switch generally similar to that of Fig. 2, but with a heater in its capsule, the heater being connected in series with the controlled contacts.

The basic structure of the capsule is welded together, and the capsule may contain a spring to assist in the definition of the temperature at which the device responds. In the devices described above the filling for the capsule is CC12F2 which is only one of a number of fluorinated halocarbons from which the capsule filling is selected. By suitable choice of the filling, the device's operating temperature can be chosen to lie anywhere in a wide temperature range, e.g. from - 200 C to +20O0C.

The characteristic on which operation depends are the curves which relate tem- perature and vapour pressure, and these curves, unlike those for the gas laws, have a logarithmic characteristic.

WHAT WE CLAIM IS:- 1. A thermal switch which includes a sealed enclosure containing a liquid halocarbon, one wall of the enclosure being a bowed disc, wherein when the temperature to which the switch is subjected passes through a preset value the fluid pressure within the enclosure changes in such a way as to cause the bowed disc to change from a concave state to a convex state or vice-versa, and wherein the change of state of the bowed disc causes a switching operation on electrical contacts forming part of the switch.

2. A thermal switch as claimed in claim 1 and wherein the halocarbon is dichloro difluoro methane (CC12F2).

3. A thermal switch as claimed in claim 1 or 2, wherein the enclosure is substantially cylindrical with the bowed disc forming one of its end faces.

4. A thermal switch as claimed in claim 3, wherein a pillar is mounted on the bowed disc outside of the enclosure, which pillar carries a movable contact for co-operation with a stationary contact.

5. A thermal switch as claimed in claim 4, wherein said movable contact is a disc on the end of the pillar and the stationary contact is a Bellevllle washer, the contact set being normally open.

6. A thermal switch as claimed in claim 4, wherein said movable contact is a disc on the end of the pillar which in the rest condition bridges two stationary contacts so that the switch has a break contact.

7. A thermal switch as claimed in any one of the preceding claims, and wherein the bowed disc moves against the urgence of a resetting spring which is adjustable.

8. A thermal switch as claimed in any one of the preceding claims, and wherein the enclosure has a heater to control the temperature to which the bowed disc responds.

9. A thermal switch substantially as described with reference to Fig. 1, 2, 3, 4 or 5 of the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. By suitably coupling these connections we produce a change-over. Fig. 3 shows a variant of the switch of Fig. 1 in which the disc 2 moves against a resetting spring 15 held in place in the structure by a set screw 16, which is adjustable to vary the effect of the spring on the disc 2. Thus when the preset temperature is reached the disc 2 flips over to engage a Belleville washer 17, the disc 2 and Belleville washer 17 being connected respectively to the terminal pins 18 and 19. Fig. 4 shows in highly schematic form how a switch such as described above can be rendered adjustable by the use of a heater 20 in the capsule: this preheats the filling to an adjustable level as decided by the variable resistor 21. Fig. 5 shows a switch generally similar to that of Fig. 2, but with a heater in its capsule, the heater being connected in series with the controlled contacts. The basic structure of the capsule is welded together, and the capsule may contain a spring to assist in the definition of the temperature at which the device responds. In the devices described above the filling for the capsule is CC12F2 which is only one of a number of fluorinated halocarbons from which the capsule filling is selected. By suitable choice of the filling, the device's operating temperature can be chosen to lie anywhere in a wide temperature range, e.g. from - 200 C to +20O0C. The characteristic on which operation depends are the curves which relate tem- perature and vapour pressure, and these curves, unlike those for the gas laws, have a logarithmic characteristic. WHAT WE CLAIM IS:-

1. A thermal switch which includes a sealed enclosure containing a liquid halocarbon, one wall of the enclosure being a bowed disc, wherein when the temperature to which the switch is subjected passes through a preset value the fluid pressure within the enclosure changes in such a way as to cause the bowed disc to change from a concave state to a convex state or vice-versa, and wherein the change of state of the bowed disc causes a switching operation on electrical contacts forming part of the switch.

2. A thermal switch as claimed in claim 1 and wherein the halocarbon is dichloro difluoro methane (CC12F2).

3. A thermal switch as claimed in claim 1 or 2, wherein the enclosure is substantially cylindrical with the bowed disc forming one of its end faces.

4. A thermal switch as claimed in claim 3, wherein a pillar is mounted on the bowed disc outside of the enclosure, which pillar carries a movable contact for co-operation with a stationary contact.

5. A thermal switch as claimed in claim 4, wherein said movable contact is a disc on the end of the pillar and the stationary contact is a Bellevllle washer, the contact set being normally open.

6. A thermal switch as claimed in claim 4, wherein said movable contact is a disc on the end of the pillar which in the rest condition bridges two stationary contacts so that the switch has a break contact.

7. A thermal switch as claimed in any one of the preceding claims, and wherein the bowed disc moves against the urgence of a resetting spring which is adjustable.

8. A thermal switch as claimed in any one of the preceding claims, and wherein the enclosure has a heater to control the temperature to which the bowed disc responds.

9. A thermal switch substantially as described with reference to Fig. 1, 2, 3, 4 or 5 of the drawings.