GB2209616A - Changeover switch - Google Patents

Abstract

A changeover switch is provided comprising first and second contact devices i.e. relays, a programmable electronic timeswitch 3, a frequency to voltage converter 4 for producing a pulse corresponding to a particular day of the week, a counter A2 for counting said pulses and a changeover circuit A3, SW1 for switching the energising of said first and second contact devices at selected intervals of one or more weeks. The first and second contact devices control respectively a duty and a standby apparatus e.g. pumps, compressors for heating, air conditioning installations. The changeover circuit comprises a counter A3 which causes the energisation of the contact devices to be switched in dependence upon the setting of a manual switch SW1 supplying pulses corresponding to every 1, 2 or 4 pulses counted by the counter A2. LEDs A, B indicate which contact device or apparatus is currently energised and LEDs 1-4 indicate the current week of operation. The time-switch 3 may provide a further output for controlling the normal daily on/off sequence of the duty apparatus. <IMAGE>

Description

CHANGEOVER SWITCH The present invention relates to changeover switches.

When apparatus such as pumps and compressors, e.g., for heating and air conditioning installations, are installed in industrial and commercial premises it is common practice to duplicate the apparatus so that there will always be a standby in the event of a failure of the duty apparatus or while maintenance is being carried out on one apparatus. Generally the arrangement is such that the standby apparatus will start automatically if the duty apparatus should fail. It is also common practice to provide a timeswitch for switching the duty apparatus on and off at selected times each day.

Unless the sequence of duty of the duplicated apparatus is changed at regular intervals, the standby apparatus can become seized-up through misuse so that in the event of a failure of the duty apparatus a complete shutdown occurs. If the apparatus is a so-called "twin" unit comprising in-built duty and standby apparatus the whole unit could require scrapping if the duty unit were to fail despite the fact that the standby apparatus should still be serviceable.

The duty sequence of the duplicate apparatus should be changed regularly, e.g., every one, two, three or four weeks, and the changeover is normally effected manually and is normally the responsibility of a maintenance engineer. Unfortunately, the changeover from one apparatus to the other is something which is frequently overlooked so that the changeovers either become very irregular or no changeover is effected ac all with the sequence thac the standby apparatus seizes-up through misuse resulting in a complete shutdown and/or uneven wear of the duplicate apparatus.

The present invention has as its object to provide a changeover switch for automatically switching the duty cycle between duplicate apparatus.

The present invention provides a changeover switch comprising first and second contact means, a programmable 7-day electronic timeswitch, means for deriving a signal from the timeswitch and producing a pulse corresponding to a particular day of the week, counter means for counting said pulses and changeover means for changing the energising of said first and second contact means from one to the other at selected intervals of one or more weeks.

The said contact means may comprise first and second sets of relay contacts to each of which one of duplicate apparatus may be connected for selectively energising one or other of the apparatus.

ks well as providing the signal for the changeover switch of the present invention, the said timeswitch may also be used to control the normal daily on/off sequence of the duty apparatus and any other apparatus requiring timeswitch operation.

Said means for deriving a signal from the timeswitch and producing an output pulse may comprise a frequency to voltage converter which converts a signal at a frequency corresponding to a particular day of the week to an output voltage. The signal from the timeswitch may be a square wave which changes in frequency with the indication of a particular day of the week, e.g., Monday.

Thus, the signal from the timeswitch may be at a particular frequency with the indication of Monday and at a higher frequency on any other day of the week and the frequency to voltage converter may be adapted to produce an output voltage at a frequency intermediate said frequencies.

Said counter means may comprise a first counter, which may be a decade counter, which counts said pulses from the frequency to voltage converter and produces a weekly output signal and said changeover means may comprise a second counter, which may be a second decade counter, which receives the signals from said first counter and changes said contact means over at the selected intervals.

Said changeover means may further comprise manually operable switch means interposed between said first and second counters whereby a said interval of one or more weeks can be selected.

Said first counter may operate over a four week cycle whereby said changeover can be effected at selected intervals of, say, one, two or four weeks.

Visual indicator means may be provided for providing a visual indication of the particular week reached in said cycle. Such visual indicator means may comprise an LED for each weeK in said cycle and a transistor connecting each said LED to the first counter, each output signal of the first counter means switching on the transistor for the appropriate week in said cycle to energise the LED indicative of that week.

Likewise, second visual indicator means may be provided for vindicating which of said first and second contact means is energised at any particular time. Such second visual indicator means may comprise an LED corresponding to each of said first and second contact means and a transistor connecting each said LED to said second counter, each output signal of the second counter switching on the transistor for the appropriate contact means to energise che LED indicative of the energised contact means.

The invention will be more particularly described with reference to the accompanying drawings, in which Figure 1 is a circuit diagram of power and relay circuits of a preferred embodiment of changeover switch according to the present invention, Figure 2 is a circuit diagram of the remaining circuits of the changeover switch of Figure 1, and Figure 3 indicates the kind and value of the components used in the circuits of Figures 1 and 2.

The power supply circuit comprises a 6V.x.

transformer 1 which steps down a 240v ac voltage to 24v ac which is then rectified and smoothed by D4 and C1 respectively to produce a voltage of approximately 30v dc which is used to power relay coils RLl and RL2. The 30v dc output is also supplied to a 15v regulator 2 which produces a stable 15v dc output for energising the circuits of Figure 2. The power supply circuit is connected to the relays RLl and RL2 by transistors T1 and T2 respectively which are selectively energised by the circuits of Figure 2.

Referring now to Figure 2 it will be seen that the circuits illustrated therein comprise a digital clock and timeswitch 3, a converter circuit 4, a counter 5 and a changeover circuit 6.

The digital clock and timeswitch 3 is a standard programmable 7-day electronic clock and timeswitch which can be used to switch equipment on and off at selected times each day. 4 signal is tapped from the timeswitch 3 by means of an electrical conductor 7, said signal being in the form of a square wave changing in frequency with the indication of "Mon" (Monday). When the timeswitch 3 is indicating "Mon" the frequency of the signal is 166he whilst on any other day of the week the signal is at 250Hz. This signal is fed into a frequency to voltage converter i.c.8 which is set up to switch its output from o to 12v at 208Hz and a resistor Ril is placed in series with the frequency to voltage to converter 8 to prevent the frequency to voltage converter affecting the operation of the clock and timeswitch 3. C2 and R7 form an RC network that determines the frequency at which the circuit will switch (208Hz) to provide a pulse through the conductor 7 only when "Mon" is indicated by the clock. Capacitor C4 smooths the switched output. The output signals from the frequency to voltage converter 8 are counted by the counter circuit 5.

Counter circuit 5 comprises a decade counter which is connected Q0 equals week 1, Q1 equals week 2, Q2 equals week 3, Q3 equals week 4 and Q4 to reset. The operation of the counter R2 is shown in Table I.

TABLE I INPUT OUTPUT PULSE FROM F to V RESET Q0 Q1 Q2 Q3 Q4 FIRST - 15v Ov 0v 0v 0v SECOND 0v 0v 15v 0v 0v 0v THIRD 0v 0v 0v 15v 0v 0v FOURTH 0v 0v 0v 0v 15v 0v FIFTH 15v 15v 0v 0v 0v 15v WEEK LED 1 2 3 4 Each output of the counter R2 will switch on a transistor T3' T4, T5 or T6 which in turn energises an LED 1, 2, 3, or 4 to indicate the week reached in a four week cycle.

The changeover circuit 6 comprises a second counter A3 which is connected Q0 equals A (Rl1 energised), Q1 equals B (RL1 de-energised) and Q2 to reset. The operation of the counter 3 is shown in Table II TABLE II INPUT OUTPUTS PULSE FROM F to V RESET Q0 Q1 Q2 FIRST - 15v 0v Cv SECOND 0v 0v 15v 0v THIRD 15v 15v 0v 15v OUTPUT LED A B outputs Q0 and Qi are connected respectively to transistors T7 and T8 which in turn energise LEDs marked B and A respectively which indicate whether relay RLl or RL2 is energised. Output Q0 of counter x3 is connected to transistor T1 which drives relay RL1 of the relay circuit.The changeover circuit 6 further includes a manually operable switch SW1 for selecting a changeover period of one, two or four weeks. In the "one week" position the output from the convertor circuit 4 is connected to the input of both counters X2 and R3. The incoming pulses move the first counter A2 on indicating weeks and the second counter A3 alternates its outputs between A and B with every pulse.With switch SW1 in the "two weeks position, outputs Q1 and Q3 of counter R2 are fed via blocking diodes D2, D3 to the second counter causing the output of the counter A3 to change at every other incoming pulse from the first counter A2 With switch SWl in the "four week" position output Q3 of counter A2 is fed directly to the second counter A3 causing the output of the second counter R3 to change on every fourth pulse. These sequences of operations are shown in Table III.

TABLE III SW1 PULSE FROM F to V WEEKLY TWO WEEKLY FOUR WEEKLY FIRST CHANGE OVER NO CHANGE NO CHANGE SECOND " " CHANGEOVER " THIRD " " NO CHANGE " " FOURTH " " CHANGEOVER CHANGEOVER FIFTH " " NO CHANGE NO CHANGE A battery backup circuit 9 is provided for use in case of a power failure. The batteries are 9 x 1.2v Ni cad. batteries which provide 10.dv for maintaining the converter circuit 4 and the counters x2 and 3 in the correct condition whilst the power is off. In addition, one cell of the battery pack is used to provide power for the clock and timeswitch 3 in the event of a power failure. Full charge of the battery pack is maintained by R2 which limits the charging current to 22m9 while the power is on. Diode D1 blocks backfeed into the power supply circuit when the power is off to prevent unnecessary discharge of the batteries. Likewise, in the event of a power failure, all of the LED's are taken to Ov via transistor Tg the base of which is connected to the 15v supply before diode D1, whereby transistor T9 switches off all of the LED's so as not to drain the batteries unnecessarily.

Preferably the power supply and relay circuits are provided on a first PCB (printed circuit board) whilst the remainder of the circuitry is provided on a second or main PCB. This allows the main PCB to be mounted as far as is practicably possible away from the mains transients and switching spikes which might occur in the power supply and relay circuits of the first PCB.

Claims (12)

1. x changeover switch comprising first and second contact means, a programmable 7-day electronic timeswitch, means for deriving a signal from the timeswitch and producing a pulse corresponding to a particular day of the week, counter means for counting said pulses and changeover means for changing the energising of said first and second contact means from one to the other at selected intervals of one or more weeks.

2. 9 changeover switch according to claim 1, wherein said contact means comprise first and second sets of relay contacts.

3. 9 changeover switch according to claim 1 or 2, wherein said means for deriving a signal from the timeswitch and producing an output pulse comprises a frequency to voltage converter which converts a signal at a frequency corresponding to a particular day of the week to an output voltage.

4. k changeover switch according to claim 1, 2 or 3 wherein said counter means comprises a first counter which counts said pulses and produces a weekly output signal and said changeover means comprises a second counter which receives the signals from said first counter and changes said contact means over at the selected intervals.

5. k changeover switch according to claim 4, wherein said first and second counters are decade counters.

6. 9 changeover switch according to claim 4, or 5, wherein said changeover means includes manually operable switch means interposed between said first and second counters whereby a said interval of one or more weeks can be selected.

7. k changeover switch according to claim 4, 5 or 6, wherein said first counter operates over a cycle of a predetermined number of weeks.

8. x changeover switch according to claim 7, wherein visual indicator means is provided for providing a visual indication of the particular week reached in said cycle.

9. x changeover switch according to claim 8, wherein said visual indicator means comprises an LED for each week in said cycle and a transistor connecting each said LED to the first counter, each output signal of the first counter means switching on the transistor for the appropriate week in said cycle to energise the LED indicative of that week.

10. 9 changeover switch according to any one of claims 4 to 9, wherein second visual indicator means is provided for indicating which of said first and second contact means is energised at any particular time.

11. 9 changeover switch according to claim 10, wherein said second visual indicator means comprises an LED corresponding to each of said first and second contact means and a transistor connecting each said LED to said second counter, each output signal of the second counter switching on the transistor for the appropriate contact means to energise the LED indicative of the energised contact means.

12. k changeover switch substantially as herein described with reference to the accompanying drawings.