GB1589264A

GB1589264A - Immersion control switch unit

Info

Publication number: GB1589264A
Application number: GB1474976A
Authority: GB
Original assignee: Horstmann Gear Co Ltd
Current assignee: Horstmann Gear Co Ltd
Priority date: 1977-07-12
Filing date: 1977-07-12
Publication date: 1981-05-07

Description

(54) AN IMMERSION HEATER CONTROL SWITCH UNIT (71) We, THE HORSTMANN GEAR COM PANY LIMITED, a British Company, of Newbridge Works, Bath BA1 3EF, Avon, 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 an immersion heater control switch unit having a by-pass or over-ride facility which is maintained by a predetermined current dmand.

These switch units are particularly useful in the control of immersion heaters which are subject to on/off thermostatic control. In the case of such applications it is useful for the purpose of energy saving to arrange that the heater is switched off when a predetermined temerpature is achieved and is not turned on again by the thermostat when this temperature drops. This enables a tank of water to be heated to the temperature set by the thermostat but avoids further unrequired heating as water is drawn off. Such a facility can be particularly useful in the case of timeswitch control of immersion heaters, which is often employed both for energy saving and for maximum demand control, as there is sometimes a requirement by the user during the time switch off period for additional water to be heated.To provide for this requirement a separate over-ride switch may be provided, but this must be re-set manually as soon as the required amount of water has been heated and if this is forgotten the timeswitch control will not operate so the heater will remain on and the energy will be wasted.

On some timeswitches, an advance facility is provided to allow switching ON during an OFF period. When this is used the timeswitch dial will take over after the next 'OFF' move.

This will not always prevent the immersion heater from operating for a longer period than is necessary.

The construction of many heaters does not allow for easy access to the thermostat circuit so that operation directly from the thermostat to revert to time switch control when the thermostat contacts open is difficult and in any case additional wiring is necessary.

This invention seeks to provide a switch with an over-ride facility in which the over-ride facility is maintained as long as a predetermined through current is maintained as long as a predetermined through current is maintained.

According to the invention, there is provided an immersion heater control switch unit comprising a pair of switch contacts controlling current feed to the immersion heater and a self holding relay having a pair of normally open relay contacts coupled across the switch contacts, the relay being biased to an open state of said relay contacts and actable against said bias to by-pass the open contacts of the switch and energise the immersion heater as long as the predetermined current through the relay is maintained A plurality of self holding relays may be coupled across the switch contacts.

The or each self holding relay may comprise a current sensing relay with its winding connected in series arrangement with said pair of normally open relay contacts which relay contacts are closable manually, the series arrangement being connected across said switch contacts.

Indicator means may be provided which is actuated upon actuation of the relay to provide an indication that the switch contacts are bypassed.

In a particularly advantageous form of the invention the switch contacts are actuable periodically by a time clock to provide a time switch having an over-ride facility which is actuable during the normally off period.

In order that the invention and its various other features may be understood more easily an embodiment thereof will now be described, by way of example only, with reference to the drawings in which: Figure 1 is a front view of a timeswitch constructed in accordance with the invention, Figure 2 is a circuit diagram showing the circuit layout of the timeswitch of Figure 1, Figure 3 is a circuit diagram of an alterna tive connection of the timeswitch over-ride facility, and Figure 4 is a circuit diagram based on Figure 2 in which three timeswitch over-ride facilities are provided.

Figure 1 shows a timeswitch having a housing 10 having a front panel 11. On the front panel there is located a time pointer 12 and a time clock dial 13 which is rotatable by a synchronous electric clock mechanism. The dial makes one revolution every 24 hours and turns in a clockwise direction. It is numbered 1-24 in hourly intervals with i hour subdivisions. The pointer 12 indicates the time shown on the dial. It is important that when setting up the timeswitch or after any interruptions of supply ot the timeswitch, that the dial reads the correct time of day in relation to the Time Pointer. The dial 13 is equipped with tappets 14 which serve to actuate switch contacts (not shown) in this case to provide one switch on and one switch off each revolution of the dial in a conventional manner.

The tappets are adjustably mounted on the dial to enable adjustment of switch on and switch off times. The front panel also carries a main two pole isolator switch 15, a neon indicator light 16 and a time switch override push button 17.

The circuit arrangement of the timeswitch is shown in Figure 2. Mounted on the housing there is a connector 18 having input connections 21 and 22 for line and neutral supply inputs respectively and output connections 23 and 24 for connection to a series connection of an immersion heater 25 and water tank thermostat 26.

The inputs 21 and 22 are coupled to the main isolator switch 15. The switch 15 is effective when closed to connect the input 22 to the output 23 and the input 21 to a connector 30 and also to one end of an armature coil 27 of a relay 28. The other end of the relay coil is connected via normally open contacts 29 of the relay to a connector 31 and also to the output 24. The neon lamp 16 is connected in series with a current limiting resistor 32 between the input 22 and the output 24.

The connectors 30 and 31 are connected to switch contacts 33 which are closeable periodically by the time clock (not shown in Figure 2).

The arrangement operates as follows:- Under time switch control the contacts 33 are closed and opened periodically and when the main switch 15 is closed, the neutral input is connected continuously to the output 23 and one side of the immersion heater 25 whilst the line input is connected periodically to the output 24 and to the other side of the immersion heater 25 via the thermostat 26. Accordingly water is heated during the time switch on period under the control of the thermostat 26. When heating of water in the tank is required during the time switch off period this can be accomplished without altering the time clock by depressing the button 17 which is coupled to the armature of the relay 28 and which effects closure of the relay contacts 29 and thus switching of the line input to the immersion heater.The current flowing to the immersion heater 25 via the armature coil 27 is sufficient to hold the relay in the operated state and so maintain the contacts 29 in the closed state. When the water in the tank is raised to a temperature set by the thermostat 26, the thermostat contacts open and this cuts off the flow of current to the immersion heater via the armature coil 27 and the relay is de-energised so that the contacts are opened under the action of suitable biassing means e.g. a spring. The heater is not re-energised via the relay 28 when the thermostat contacts close again unless the button 17 is again depressed.It will be clear that depression of the button 17 enables a predetermined quantity of water, which depends on the quantity of water in the tank and the position of the thermostat to be raised to a predetermined temperature and that no energy wastage as a result of failure to switch off the heater results as would occur in the case of conventional manual switch override facilities. In addition the time switch facility operates continuously and reversion to time switch control occurs at the end of the over-ride function. The neon lamp 16 is energised and illuminated whenever a line voltage is available at the output 24 and therefore is illuminated to provide an indication that the ime switch "ON" period is in force or that the over-ride facility is in operation.

Various alternative arrangements can be made for providing an audible or visual indication mechanically or electrically, that the over-ride cycle is in operation or has been completed. For example a mechanical indicator could be in the form of a flag attached to the moving armature of the relay. As this armature moves, the flag would be displayed through a window in the front panel of the housing and would therefore show the position of the armature and hence when it is no longer controlling the heating load.

Similarly, an electrical indication may be given by means of an indicator lamp or buzzer which may be switched on by means of auxiliary contacts mounted on the relay armature which would close the circuit to operate the lamp or buzzer when the heating circuit is broken.

Although the embodiment described has time switch contacts on the line input only it will be appreciated that ganged contacts could also be provided on the neutral input so that the time switch effects isolation of the outputs 23 and 24. In such a construction an additional pair of contacts would be provided on the relay 28 which would be closeable on operation of the relay to bypass the additional contacts of the time switch to effect the over ride function.

Although the preferred embodiment of the invention provides over-ride facility for switch contacts which are operated by a time mechanism the switch contacts may be operable by any other alternative means e.g.

manually or by a machine function.

Figure 3 shows an alternative connection between the relay 28 and switch contacts 33 which can be employed in the circuit layout of Figure 2. In this connection the switch 15 is coupled to the connector 30 via the armature coil 27 and the normally open relay contacts 29 are connected directly in parallel with the switch contacts 33. In this way when the button 17 is depressed current is fed to the immersion heater via the relay contacts 29, and 33 in parallel and the relay is maintained in that state even though contacts 33 are closed and provides a current path through the contacts 29 if the contacts 33 are subsequently opened, due to the completion of a time period, so long as there is a current demand due to the thermostat contacts being closed. As soon as the thermostat contacts open the relay is de-energised and the contacts 29 open.The heater is not re-energised when the thermostat contacts close again unless the button 17 is depressed. The alternative arrangement is useful in that at the end of a timed period provided the button 17 has been depressed and the relay is in the maintained state the heater will continue to operate until the tank of water is raised to a temperature set by the thermostat 26 and thereby ensures a reserve of hot water for use in the timeswitch off period.

In the circuit of Figure 3 the self maintaining relay 28 may be arranged to be also self actuating so that it is actuated automatically when current is fed to the immersion heater via the contacts 33 and is maintained when the contacts 33 open at the end of the time period as long as the thermostat contacts are closed. This ensures that there will always be a full tank of hot water at or after the expiry of the time period but suffers from the disadvantage that the relay is actuated each time the thermostat closes during the timeswitch "on" period.

The relay may be a double wound relay one winding providing a purely self maintaining facility and the other winding providing a self actuating function and means may be provided for selecting which type of operation is required for example by means of a function selector switch.

Figure 4 shows another circuit, based on the circuit of Figure 2, for operating a plurality of relays (in this case 3) 34, 35, 36 in conjunction with separate immersion heaters 37, 38, 39.

These immersion heaters can be arranged each in a respective tank or with two or more in one tank in order to provide over-ride facilities in respect of different quantities of water by, for example, providing immersion heaters of different length or to provide override facilities in respect of different temperatures of water. In these cases it is necessary to employ some means for isolating the immersion heaters one from another and in this example this is effected by means of auxiliary contacts 40, 41, 42 on the relays, which open circuit the current path to the immersion heater via the contacts 33.

It will be appreciated that the circuit configuration of Figure 3 can be employed for a plural heater operation similar to the configuration of Figure 4.

WHAT WE CLAIM IS: 1. An immersion heater control switch unit comprising a pair of switch contacts controlling current feed to the immersion heater and a self holding relay having a pair of normally open relay contacts coupled across the switch contacts, the relay being biased to an open state of said relay contacts and actuable against said bias to bypass the open contacts of the switch and energise the immersion heater as long as a predetermined current through the relay is maintained.

2. A switch unit as claimed in claim 1, wherein a plurality of self holding relays are coupled across the switch contacts.

3. A switch unit as claimed in claim 1 or 2, wherein the or each self holding relay comprises a current sensing relay with its winding connected in series arrangemet with said pair of normally open relay contacts which relay contacts are closable manually, the series arrangement being connected across said switch contacts.

4. A switch unit as claimed in claim 1 or 2, wherein the or each self holding relay comprises an armature winding connected in series with said switch contacts which switch contacts are connected in parallel with the pair of normally open contacts of the relay.

5. A switch unit as claimed in claim 4, wherein the br each relay is self energising in response to current through its armature winding.

6. A switch unit as claimed in any preceding claim, wherein one of said pair of normally open relay contacts of the or each relay is coupled with one of said pair of switch contacts and the other of said pair of normally open relay contacts is coupled with the other said pair of switch contacts via a pair of normally closed contacts of said relay.

7. A switch unit as claimed in any one of the preceding claims, including indicator means which is actuated upon actuation of the or each relay to provide an indication that the switch contacts are bypassed.

8. A switch unit as claimed in any one of the preceding claims including indicator

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. contacts of the time switch to effect the over ride function. Although the preferred embodiment of the invention provides over-ride facility for switch contacts which are operated by a time mechanism the switch contacts may be operable by any other alternative means e.g. manually or by a machine function. Figure 3 shows an alternative connection between the relay 28 and switch contacts 33 which can be employed in the circuit layout of Figure 2. In this connection the switch 15 is coupled to the connector 30 via the armature coil 27 and the normally open relay contacts 29 are connected directly in parallel with the switch contacts 33. In this way when the button 17 is depressed current is fed to the immersion heater via the relay contacts 29, and 33 in parallel and the relay is maintained in that state even though contacts 33 are closed and provides a current path through the contacts 29 if the contacts 33 are subsequently opened, due to the completion of a time period, so long as there is a current demand due to the thermostat contacts being closed. As soon as the thermostat contacts open the relay is de-energised and the contacts 29 open.The heater is not re-energised when the thermostat contacts close again unless the button 17 is depressed. The alternative arrangement is useful in that at the end of a timed period provided the button 17 has been depressed and the relay is in the maintained state the heater will continue to operate until the tank of water is raised to a temperature set by the thermostat 26 and thereby ensures a reserve of hot water for use in the timeswitch off period. In the circuit of Figure 3 the self maintaining relay 28 may be arranged to be also self actuating so that it is actuated automatically when current is fed to the immersion heater via the contacts 33 and is maintained when the contacts 33 open at the end of the time period as long as the thermostat contacts are closed. This ensures that there will always be a full tank of hot water at or after the expiry of the time period but suffers from the disadvantage that the relay is actuated each time the thermostat closes during the timeswitch "on" period. The relay may be a double wound relay one winding providing a purely self maintaining facility and the other winding providing a self actuating function and means may be provided for selecting which type of operation is required for example by means of a function selector switch. Figure 4 shows another circuit, based on the circuit of Figure 2, for operating a plurality of relays (in this case 3) 34, 35, 36 in conjunction with separate immersion heaters 37, 38, 39. These immersion heaters can be arranged each in a respective tank or with two or more in one tank in order to provide over-ride facilities in respect of different quantities of water by, for example, providing immersion heaters of different length or to provide override facilities in respect of different temperatures of water. In these cases it is necessary to employ some means for isolating the immersion heaters one from another and in this example this is effected by means of auxiliary contacts 40, 41, 42 on the relays, which open circuit the current path to the immersion heater via the contacts 33. It will be appreciated that the circuit configuration of Figure 3 can be employed for a plural heater operation similar to the configuration of Figure 4. WHAT WE CLAIM IS:

1. An immersion heater control switch unit comprising a pair of switch contacts controlling current feed to the immersion heater and a self holding relay having a pair of normally open relay contacts coupled across the switch contacts, the relay being biased to an open state of said relay contacts and actuable against said bias to bypass the open contacts of the switch and energise the immersion heater as long as a predetermined current through the relay is maintained.

means which is actuated when the or each said relay is in said open state to provide an indication that the switch contacts are not bypassed.

9. A switch unit as claimed in Claim 7 or 8, wherein the or each indicator means comprises an indicator element movable by the armature of the relay to provide a visible indication of the operational state of the or each relay.

10. A switch unit as claimed in Claim 7 or 8, wherein the or each indicator means comprises for the or each relay an additional pair of relay contacts operatively coupled with an audible or visible indicator device.

11. A switch unit as claimed in Claim 7, wherein the or each indicator means comprises an indicator device electrically coupled to the output contact of said pair of switch contacts of its associated relay and actuable upon closure of the relay contacts.

12. A switch unit as claimed in Claim 10 or 11, wherein the or each indicator means comprises an electric indicator lamp.

13. A switch unit as claimed in any preceding claim having first and second inputs for connection to opposite sides of a source of supply potential the first input being coupled to a first output and the second input being coupled via the said switch contacts to a second output.

14. A switch unit as claimed in Claim 13, wherein the switch has a second pair of switch contacts which are closeable with said switch contacts and which are connected in circuit between the first input and first output to enable isolation between inputs and outputs, and the or each relay has a pair of contacts arranged to bridge said second pair of switch contacts when the relay is actuated.

15. A switch unit as claimed in Claim 13, including an isolator switch having two pairs of ganged isolator contacts which are closeable together, one pair of isolator contacts being connected in series between the first input and the first output and the other pair of isolator contacts being connected in series between the second input and said switch contacts and second output.

16. A switch unit as claimed in any preceding claim, wherein said switch contacts are actuable periodically by a time clock.

17. An immersion heater installation comprising one or more immersion heaters coupled with a source of supply potential via a series arrangement of a respective thermostatically operable switch and a switch unit as claimed in any preceding claim, the arrangement being such that with said switch contacts open, actuation of the or each relay effects energisation of the immersion heater or a respective one of the immersion heaters from said supply potential which actuation is maintained until the energisation is cut off upon operation of its associated thermostatically operable switch at a predetermined water temperature.

18. A switch unit substantially as described herein with reference to and as illustrated in the drawings.

19. An immersion heater installation substantially as described herein with reference to and as illustrated in the drawings.