GB2071913A - Thermostat - Google Patents

Abstract

A thermostat particularly for controlling a central heating installation has three push buttons 16, 17, 18, operation of which selects three different temperatures at which the installation is then controlled. The temperatures represent frostguard, background and comfort levels and may be achieved by moving a pivoted lever 12 through different angles. A bimetallic strip 11 has one end mounted on the lever 12 and the other end secured to an over-centre spring 13. A microswitch 14 is operated when the spring goes over centre. Other embodiments described have expansible capsules or bellows or thermistors as their temperature sensing means. <IMAGE>

Description

SPECIFICATION Thermostats This invention relates to thermostats of the kind which operate electrical switch means at a predetermined sensed temperature.

The invention provides a thermostat connected to operate electrical switch means and having selecting means for selecting two or more different temperatures at which the electrical switch means is operated.

Preferably the selecting means comprises two or more manually operable push buttons.

The thermostat may have a bimetallic strip sensing ambient temperature and located to operate said electrical switch means, and said selecting means may operate to apply different biases to said strip for the different temperatures. Said selecting means may move the strip toward or away from said switch means. There may be an over-centre spring device operated by said strip when the selected temperature is achieved.

Alternatively the thermostat may be an expansible capsule or bellows.

The thermostat may be thermistor and the electrical switch means a Schmidt type trigger device responsive to the thermistor output. The selecting means may be a plurality of biasing resistors connected to the trigger through selecting switches.

Specific embodiments of different forms of the invention are shown in the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a bimetallic strip thermostat, Figure la is a detail of a push button of Figure 1, Figure 2 is a diagrammatic representation of a capsule thermostat, Figure 3 is a diagrammatic representation of an electronic thermostat, and Figure 4 is an exterior perspective view of a thermostat according to the invention.

Referring first to Figure 1, a thermostat for sensing a room temperature has as its temperature-sensing element a bimetallic strip 11. The strip is secured at one end to an adjustable mount 12, and at its other end to an over-centre spring device 13. Adjacent the over-centre spring device is a microswitch 14 located to be operated by the end of the bimetallic strip as it senses increased temperature and bends upwardly.

It will be seen that the over-centre spring device 13 opposes upward movement of the bimetallic strip until it reaches its unstable central position when it snaps over into a position of opposite curvature to that shown in the drawing, causing the strip to move rapidly upwardly and operate the microswitch.

The mounting 12 carrying the opposite end of the bimetallic strip has an arm which is pivotally mounted at 15 to provide for up and down movement of the bimetallic strip. Three push-button operated abutments 16, 17, 18 are lined up along the arm at different radii from the pivot point 15. A spring 19 tends to maintain or return the arm to its lowest position. When any of the push buttons is operated its abutment pushes the arm up against the resistance of spring 19 and holds the arm in that position until it is released by the operation of another button. This upward movement moves the end of the bimetallic strip up and thereby alters the temperature at which the over-centre spring will snap over and the microswitch will be operated.

Since the push buttons are at different radii from the pivot point, the same upward linear motion from each one will provide a different upward motion of the bimetallic strip and thereby a different sensed temperature at which the microswitch is operated.

In this specific example, the three different sensed temperatures are a frost protection temperature of say 40"F, a background temperature of say 65"F, and a comfort temperature of say 70"F. The microswitch is connected into a heating appliance circuit heating the space in which the thermostat is located, e.g. into a central heating system having a radiator in the space. When the microswitch has not been operated, more heat is called for, until the selected temperature is reached. By simple manual operation of the selected push button, the central heating system can be operated as a frost protection, e.g. overnight or when the space is unoccupied, or can be operated to give background heat only, or can be operated to give a higher comfort level, for instance when the occupants are not active.

Figure 4 shows the thermostat as it would be mounted in the space to be heated with the push buttons marked appropriately. An actual temperature indication is shown at 20 so that the operation of the heating appliance can be checked.

While the selected temperature may be fixed, there is shown in Figure la means for adjusting the selected temperature. Each push button has a removable cap 41 allowing access to a screw 42. By turning the screw the abutment may be moved toward or away from the arm so altering the movement imparted by the push button to the arm and so the selected temperature.

A similar effect can be obtained by the diagrammatic representation of Figure 2. This has an expansible capsule 22 as its temperature sensitive element. The capsule is filled with a fluid which expands and contracts with the varying temperature so causing the sides of the capsule to flex. As the capsule expands it contacts, directly or indirectly, a microswitch 24. In order to select different temperatures the capsule 22 is adjustably movable up and down with respect to the microswitch by different amounts. The Movements are provided by three push buttons 25, 26, 27 arranged to give incremental movements to a pivoted lever 28 on which the capsule 22 is mounted. The lever 28 is mounted at one end in a fixed support 29 so that its movement is substantially up or down, so adjusting the position of the capsule.A spring 21 returns the lever to its original position when the buttons are released. In an alternative version the capsule is replaced by a bellows and phial temperature sensor.

Another way of carrying out the invention using electronic components is shown diagrammatically in Figure 3. A Schmidt type trigger circuit 30 receives an electrical input on line 31 from a temperature sensor, e.g. a thermistor 44, the electrical input being related to the sensed temperature.

Comfort, frostguard and background temperatures are set by switching in combinations of resistors 33, 34, 35 via switches S1 and S2. The resistors may be variable so that the set temperature can be altered. The selected resistance is connected to the trigger circuit on line 31 together with the thermistor output. The trigger circuit produces an output on line 40 to operate relay 45 when the threshold set by the selected resistance is exceeded.

Feedback resistance 46 ensures sharp switching as the trigger starts to turn on. Push buttons (not shown) operate switches S1, S2 in appropriate combinations.

As with the other embodiments, operation of the push buttons therefore selects which temperature level sensed will produce an output. The output may be used to control a central heating installation or other heating appliance, so as to achieve the temper ature level selected.

The push buttons in all three embodiments may be latched by a conventional latch bar mechanism shown in Figures 1 and la at 43 so as to stay in the operated position until released by operation of another button.

There may be an additional "off' button (not shown) which operates effectively to shut the central heating installation off.

Claims (15)

1. A thermostat connected to operate electrical switch means and having selecting means for selecting from two or more different temperatures at which the electrical switch means is to be operated.

2. A thermostat as claimed in claim 1, wherein said selecting means comprises two or more manually operable push buttons.

3. A thermostat as claimed in claim 1 or claim 2, including means for adjusting said different temperatures.

4. Athermostat as claimed in any of claims 1 to 3, having a bimetallic strip for sensing ambient temperature, located to operate said electrical switch means, said selecting means operating to apply a different bias to the said strip for each different selected temperature.

5. A thermostat as claimed in claim 4, as appendank to claim 2, wherein each push button when operated pushes the strip toward the switch means by a predetermined distance.

6. A thermostat as claimed in claim 5, wherein there is an overcentre spring device operated by said strip when the selected temperature is sensed.

7. A thermostat as claimed in claim 4 or claim 5, wherein one end of the strip is mounted on a pivoted arm, the selecting means operating to move the arm about its pivot.

8. Athermostat as claimed in any of claims 1 to 3, having an expansible capsule for sensing ambient temperature, located to operate said electrical switch means, said selecting means operating to move the capsule toward the electrical switch means by a different amount for each different selected temperature.

9. A thermostat as claimed in claim 8, wherein said capsule is mounted on a pivoted lever, the selecting means operating to move said lever.

10. Athermostat as claimed in any of claims 1 to 3, having a bellows and phial for sensing ambient temperature.

11. Athermostat as claimed in any of claims 1 to 3, having a thermistor for producing an electrical output related to ambient temperature and an electrical circuit controlling a relay operating said electrical switch means.

12. A thermostat as claimed in claim 11, wherein said selecting means connect selected resistances into said electrical circuit, the values of the resistances being related to the selected temperatures.

13. Athermostat as claimed in claim 2 or any claim appendantthereto, having a latching bar for holding a push button in the operated position until released by operation of another button.

14. A thermostat as claimed in any of claims 1 to 13, for use in controlling a central heating installation, there being three different selected temperatures, a low temperature above freezing point, a medium, background, temperature, and a higher, comfort, temperature.

15. Athermostat substantially as described hereinbefore with reference to Figures 1, la and 4, Figure 2 or Figure 3 of the accompanying drawings.