GB2122390A

GB2122390A - Electronic thermostat

Info

Publication number: GB2122390A
Application number: GB08314272A
Authority: GB
Inventors: Michael Leonard Kelly; Colin Baker
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-05-24
Filing date: 1983-05-23
Publication date: 1984-01-11
Also published as: GB8314272D0; GB2122390B

Abstract

A thermostat comprises a sensor (22) in the form of a thermistor for sensing ambient temperature and a digitally controllable reference signal source comprising a plurality of resistances (26) connectable in parallel by respective switches (24) so that the reference signal is variable in discrete steps. The thermistor and the plurality of resistances (26) form connected arms of opposite sides of a Wheatstone bridge circuit, the voltage difference between the thermistor and the resistance arms being used to control a power switch (18) controlling a heating system. A user-actuable switch (27) is provided which when depressed causes the reference signal source to vary the reference signal in discrete steps. <IMAGE>

Description

SPECIFICATION Electronic thermostat THE PRESENT INVENTION relates to thermostats such as are used in hotels, offices and houses for the control of room heating, central heating and zone heating systems.

Accordingly, the present invention provides a thermostat comprising a sensor for sensing ambient temperature and providing a signal which is variable in dependence thereon, a reference signal source means for comparing said signals and providing a control signal dependent on the comparison, the reference signal source being digitally controllable for providing a reference signal variable in discrete steps and a user-actuable switch which when depressed causes the reference signal source to vary the reference signal in discrete steps.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawing which is a schematic diagram of a preferred embodiment of the present invention.

The drawing shows a thermostat 10 which has a D.C. voltage source 12 supplying an operating voltage to opposing corners of a Wheatstone bridge circuit 14, the remaining corners of which are connected to respective inputs of voltage comparator 1 6 in turn driving a power switch 18. The latter may be in the form of a relay or solid-state switch such as a triac controlling a solenoid valve, heat exchanger fan or pump or the like in a typical heating or air conditioning system in the normal manner.

As with known thermostats the two resistances 20 connected to one terminal of the voltage source 1 2 are fixed resistances, normally equal in value, while the third resistance 22 is a temperature dependent resistance, normally a negative temperature coefficient thermistor. In the preferred embodiment of the present invention, however, the fourth resistance of the bridge, normally a potentiometer, is replaced by a set of parallel resistance arms each comprising a fixed value resistance 24 and a series connected switch 26. Each of the resistances 24 has a value chosen to provide a unique discrete temperature setting when the corresponding switch 26 is closed and the remaining switches open.

The switches 26 are electrically controlled by a control circuit 28 which operates to actuate the switches 26 in a sequential manner. The switches 26 can be controlled so that only one switch is closed at any one time or such that a selected combination of switches is controlled to provide a greater number of temperature settings than there are resistances 24. The control circuit 28 is conveniently a counter which can be locked under control of a user-actuable switch 27 in the form of a push-button or the like by an operator to actuate the switches 26 in the preselected sequence until the desired temperature setting is set by the resistances 24 and switches 26.

The arrangement may be such that the counter steps through one step to actuate a successive switch each time the push-button is pressed. Alternatively, the arrangement can be such that the counter continues to count at a sufficiently slow rate while the push button is maintained pressed until the desired temperature setting is achieved.

A temperature setting indicator 32 may be provided to indicate, for example, using lightemitting diodes, the desired temperature setting, the indicator also being controlled by the control circuit 28. The light-emitting diodes 33 can be arranged to provide a digital readout or simply located adjacent a calibrated temperature scale. CMOS integrated circuits are preferably used for the reference voltage source switches 26 (which may comprise a CMOS analogue switch circuit), control circuit and indicator.

The above-described thermostat provides a greater temperature accuracy because of its use of fixed value resistors which may have tolerances as little as 1%. In addition, the use of fixed value resistances allows the gradient of the temperature control range to be selected to suit particular requirements.

In addition, the thermostat according to the present invention is capable of being remotely controlled. The control circuit 28 does not have to be located adjacent the reference voltage source and can be positioned in, for example, a control room in a building and used to control several thermostats positioned in various rooms in the building. In addition, the control circuit may be preprogrammed to adjust the temperature setting automatically to take account of variations in building.

1. A thermostat comprising a sensor for sensing ambient temperature and providing a signal which is variable in dependence thereon, a reference signal source, means for comparing said signals and providing a control signal dependent on the comparison, the reference signal source being digitally controllable for providing a reference signal variable in discrete steps and a user-actuable switch which when depressed causes the reference signal source to vary the reference signal in discrete steps.

2. A thermostat according to Claim 1, wherein, the number of discrete steps by which the reference signal is varied when the control switch is depressed is determined by the time period for which the user-actuable switch is depressed.

3. A thermostat according to Claim 1, wherein, each time the user actuable switch is

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electronic thermostat THE PRESENT INVENTION relates to thermostats such as are used in hotels, offices and houses for the control of room heating, central heating and zone heating systems. Accordingly, the present invention provides a thermostat comprising a sensor for sensing ambient temperature and providing a signal which is variable in dependence thereon, a reference signal source means for comparing said signals and providing a control signal dependent on the comparison, the reference signal source being digitally controllable for providing a reference signal variable in discrete steps and a user-actuable switch which when depressed causes the reference signal source to vary the reference signal in discrete steps. The present invention is further described hereinafter, by way of example, with reference to the accompanying drawing which is a schematic diagram of a preferred embodiment of the present invention. The drawing shows a thermostat 10 which has a D.C. voltage source 12 supplying an operating voltage to opposing corners of a Wheatstone bridge circuit 14, the remaining corners of which are connected to respective inputs of voltage comparator 1 6 in turn driving a power switch 18. The latter may be in the form of a relay or solid-state switch such as a triac controlling a solenoid valve, heat exchanger fan or pump or the like in a typical heating or air conditioning system in the normal manner. As with known thermostats the two resistances 20 connected to one terminal of the voltage source 1 2 are fixed resistances, normally equal in value, while the third resistance 22 is a temperature dependent resistance, normally a negative temperature coefficient thermistor. In the preferred embodiment of the present invention, however, the fourth resistance of the bridge, normally a potentiometer, is replaced by a set of parallel resistance arms each comprising a fixed value resistance 24 and a series connected switch 26. Each of the resistances 24 has a value chosen to provide a unique discrete temperature setting when the corresponding switch 26 is closed and the remaining switches open. The switches 26 are electrically controlled by a control circuit 28 which operates to actuate the switches 26 in a sequential manner. The switches 26 can be controlled so that only one switch is closed at any one time or such that a selected combination of switches is controlled to provide a greater number of temperature settings than there are resistances 24. The control circuit 28 is conveniently a counter which can be locked under control of a user-actuable switch 27 in the form of a push-button or the like by an operator to actuate the switches 26 in the preselected sequence until the desired temperature setting is set by the resistances 24 and switches 26. The arrangement may be such that the counter steps through one step to actuate a successive switch each time the push-button is pressed. Alternatively, the arrangement can be such that the counter continues to count at a sufficiently slow rate while the push button is maintained pressed until the desired temperature setting is achieved. A temperature setting indicator 32 may be provided to indicate, for example, using lightemitting diodes, the desired temperature setting, the indicator also being controlled by the control circuit 28. The light-emitting diodes 33 can be arranged to provide a digital readout or simply located adjacent a calibrated temperature scale. CMOS integrated circuits are preferably used for the reference voltage source switches 26 (which may comprise a CMOS analogue switch circuit), control circuit and indicator. The above-described thermostat provides a greater temperature accuracy because of its use of fixed value resistors which may have tolerances as little as 1%. In addition, the use of fixed value resistances allows the gradient of the temperature control range to be selected to suit particular requirements. In addition, the thermostat according to the present invention is capable of being remotely controlled. The control circuit 28 does not have to be located adjacent the reference voltage source and can be positioned in, for example, a control room in a building and used to control several thermostats positioned in various rooms in the building. In addition, the control circuit may be preprogrammed to adjust the temperature setting automatically to take account of variations in building. CLAIMS

3. A thermostat according to Claim 1, wherein, each time the user actuable switch is depressed, the reference signal is varied by one discrete step.

4. A thermostat according to Claim 1, 2 or 3, wherein the reference signal is determined by a plurality of resistances connectable in parallel by respective resistance connector switches.

5. A thermostat according to Claim 4, wherein the resistance connector switches are closed in response to clock pulses from a counter actuated by the user-actuable switch so that the resistance connector switches are closed in a preselected sequence.

6. A thermostat substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

7. Any novel feature or combination of features described herein.