GB2230340A - Service interval indicator - Google Patents

Abstract

A service interval indicator, for connection to a device the service interval of which is to be measured, comprises counter means U1 to U3 which count mains pulses while the device is energized, and a red LED (light emitting diode) LED2, and a green LED LED1 in close juxtaposition. The counter means energizes LED1 up to a count slightly above the nominal service interval and LED2 from a count slightly below that interval, so that amber/yellow (green plus red) indicate the servicing is due and red indicates that it is overdue. The indicator may be directly mains powered and connected across or in one of the mains to the apparatus whose service interval is to be indicated where it preferably includes a triac TR1 with a zener diode ZD1 and resistor R2 connected in series across the triac and the triac gate connected to the junction of the zener diode and resistor. Pulses are developed across the triac, and these pulses are rectified (D2, C2) to provide a power supply for the counting means and fed to the counting means to be counted <IMAGE>

Description

Service III t erval Id ica t or The present invention relates to a service interval indicator; that is, to means which accumulate the total operating time of an electrical device and indicate when the total time reaches a predetermined value. The value is normally chosen as that at which the device should be serviced in some way.

Many electrical devices are designed to require servicing at predetermined intervals. Examples of such devices are certain types of lighting appliance (which may require the lighting elements to be changed either to minimize the possibility of the elements burning out or because their lighting efficiency falls with time), video recorders (which should have their heads cleaned at suitable intervals), and microwave cookers (for which testing for leakage may be desirable at suitable intervals).

These intervals ought to be measured by the accumulated operating time (on time) of the device. This is however not easily measured. A calendar measurement is often used, the interval being taken as, e.g., a week or a quarter. If the usage of the device is substantially constant and unchanging throughout the year, such a measurement may be reasonable. However, in many instances the usage of the device may vary widely between substantially continuous service and only rare use. A simple calendar measurement is therefore often totally inappropriate. What is required is timer means which accumulates only the on time of the device.

Such timer means might be constituted by a mechanical clock, which is energized when the device is turned on. This is however unsatisfactory for a variety of reasons. For example, a mechanical counter tends to be expensive and inconveniently bulky, and the indication from it may tend to be overlooked.

Accordingly the present invention provides a service interval indicator for connection to a device the service interval of which is to be measured, the indicator comprising counter means which count mains pulses while the device is energized, and signalling means operable at predetermined counts of the counter to give an indication when the counter reaches predetermined a count or counts.

To ensure that the count of the service interval indicator is not lost if it is disconnected from the mains1 it may incorporate 8 back-up battery to preserve the count in the counters; alternatively, the counters may be of a type the state of which is not lost on loss of power.

The predetermined count or counts may be set stable by means of internal setting means.

The signalling means preferably comprise a plurality of differently coloured lighting elements1 which preferably consist of a red LED (light emitting diode) and a green LED in close juxtaposition, and the counter means preferably energizes the green LED up to a count slightly above the nominal service interval and the red LED from a count slightly below that interval.

The service interval indicator may be directly mains powered and connected across the mains to the apparatus whose service interval is to be indicated (with, obviously, the mains switch of the apparatus between the service interval indicator and the main supply). Preferably, however, it is connected in one of the mains supply lines. to the apparatus. In the latter case, it may be incorporated in a connector1 such as an in-line connector, a plug and socket adaptor, or a plug which is wired to the apparatus.

If the service interval indicator is connected in a mains supply line, it preferably includes a triac with a zener diode and resistor connected in series across the triac and the triac gate connected to the junction of the zener diode and resistor. Pulses are developed across the triac1 and these pulses are rectified to provide a power supply for the counting means and fed to the counting means to be counted.

The service interval indicator may of course measure the accumulated operating time of some particular portion of an electrical system; for example, the accumulated operating time of a record player forming part of an audio system (to indicate when the stylus should be replaced). If the relevant part of the system does not have its own mains switch, then the service interval indicator would be controlled by whatever internal combination of signals causes that part of the system to operate.

A mains adaptor embodying the invention will now be described, by way of example, with reference to the drawings, in which: Fig. 1 shows a 13A 3-pin adaptor embodying the invention; and Fig. 2 is a circuit diagram of the adaptor.

The invention is shown as embodied in a 3-pin adaptor 10, Fig. 1, having a conventional 3-pin plug 1; on one face and a conventional 3-pin socket 12 on the opposite face. The adaptor has a sloping face 13, formed between its socket face and its upper face, with an indicator 14 and a small recess 15 located on it.

As far as the user is concerned, the pins 11L, 11N, and 11E of the plug 11 are connected straight through to the pins 12L, 12N, and 12E of the socket 12.

The plug 11 of the adaptor is plugged into a mains socket, and some apparatus, such as a microwave cooker or a video recorder, is plugged into the socket 12.

When: the mains socket is switched on and the apparatus plugged into the adaptor is turned on, the indicator 14 will be lit. If the apparatus plugged into the adaptor is put into the stand-by mode (powered up, e.g. to keep internal clock and timer circuits running, but not. operating; or is turned off completely, or if the mains socket is turned off, the indicator 14 will turn off.

The indicator 14 will be green initially, but will change colour when the apparatus plugged into the adaptor is due to be serviced, i.e. has been operated for an appropriate period. This period can be set to any one of a range of predetermined values (e.g. 125 hrs increasing to 8000 hrs by steps of 2:1 ratio) by taking the adaptor 10 apart and setting internal switching appropriately; the adaptor casing is made in two parts (not indicated) for this purpose. The indicator 14 changes colour first to amber/yellow, and then to red; it stays at amber/yellow for approximately a tenth of the period set into the adaptor. A switch SW3 (Fig. 2) is located at the bottom of the recess 15, and by pressing this switch with a suitable implement, the adaptor can be reset to change the indicator 14 back to green and start measuring the preset period again.The recess 15 may alternatively be located on the bottom face of the adaptor.

Fig.-2 shows the circuitry which is incorporated into the adaptor. As seen, the connections between the N and E pins and sockets are direct from pin to socket, but the connection between the L pin and socket is through the circuitry shown. There are two main sections to the circuitry1 an analog part and a digital part.

In the analog part of the circuitry, the L pin 11L is connected to the L socket 12L through a triac TR1. A 10 nF capacitor C1 is connected across the triac to protect it from possible rapid voltage rises when the mains is switched on, and a 470 Q resistor R1 is also connected across the triac1 to provide a path for low currents to enable the apparatus plugged into the adaptor to remain on in stand-by mode without the triac having to. be turned on or the timing circuitry to operate. A switch SW1 is provided to allow the resistor RI to be switched out of circuit; this switch will be accessible by taking the adaptor apart.Clearly resistor R1 and/or switch SW1 can be omitted if desired; alter natively, a multi-pole switch and a graded set of resistors can be used to allow the stand-by current limit to be selected. Even with no resistor, capacitor C1 will allow a small by-pass current to flow.

The gate of triac TR1 is connected to the junction of a 5 V zener diode ZD1 and a 10 kQ resistor R2 connected across TR1 as shown. Assuming that the mains is turned on and the apparatus plugged into the adaptor is turned on by its own switch (assuming that that apparatus incorporates a switch), triac TR1 has to be turned on substantially permanently, to complete the line voltage connection to that apparatus. This is achieved as follows. Each time the mains voltage (or, more precisely, the mains current) passes through zero, the triac will turn off. If the mains voltage is rising positively, zener diode ZD1 will turri on when the mains voltage reaches 5 V, and the triac will be turned on shortly afterwards (after a further rise of 1 to 2 V). If the mains voltage is rising negatively, then the triac will be turned on alomst immediately, as soon as the mains voltage reaches -1 to -2 V. The voltage to apparatus will therefore be the mains voltage, modified slightly by having a small initial part of each half-cycle clipped to zero.

When the apparatus plugged into the adaptor is operating; there will thus be a voltage pulse of 6 to 7 V appearing across TR1 once every cycle. These pulses are rectified by a diode D2 and the rectified pulses smoothed by a 10 pF capacitor C2, to provide a power supply for the digital part of the circuitry.

A 3 V back-up battery BT1 is connected ,to the capacitor C2 via a diode D1, to maintain the power supply when the mains supply or the apparatus plugged into the adaptor is turned off. (Of course, a rechargeable battery could be used, in which case the diode D1 would be omitted.) The digital part of the circuitry uses devices which can maintain their states and draw very little power at 3 V.

The major part of the digital part of the circuitry consists of a chain of three counters U1 to U3. Counter U1 is fed with the pulses generated by the triac TR1 and its control circuit ZD1-R2, and can count at two rates, corresponding to 50 Hz and 60 Hz mains supplies. Counters U2 and U3 effect the major part of the dividing down of the mains frequency. The connection between these two counters is switchable to allow setting of the desired service time, and counter U3 controls the two changes from green to amber/yellow and from amber/ yellow to red.

In more detail, the pulses from the triac TR1 are fed via a 10 kQ resistor R3 and an AND gate G4 to the count down input of, counter Ul1 which is a 4-stage binary counter. This counter has a borrow output B which goes to 1 when the count cycles downwards through 0, and is connected to a load control input L.

It has a 4-bit load input, which is fed with 10X1, where X = 0 or 1 dependihg on whether a switch SW4, accessible by taking the adaptor apart, is closed or open.

The counter is thus loaded to 1001 or 1011, i.e. 9 or 11, each time its count reaches 0, and counts down from the count so loaded. The total number of counts in a full cycle of the counter is therefore 10 or 12.

The setting of the switch SW4 enables the nominal times set in the adaptor to be reduced by a factor of 5/6. One application of this is for use with US mains, since the ratio of UK:US mains frequency ratio is 5:6; reducing the effective counting rate compensates for the increased frequency. If desired, similar arrangements can be provided to enable the counting rate to provide other and/or further interpolations between the 2:1 steps provided by a switch SW2 (discussed below).

Counter U2 is a 14-stage binary counter, which counts the pulses produced by U1. Its top 7 stages feed 7 pins of an 8-way selector switch SW2, which feeds counter U3. Switch SW2 is set to the appropriate position by taking the adaptor apart.

Counter U3 is also a 14-stage binary counter, which counts the pulses coming from the switch SW2. Its 11th and 14th stages feed a NAND gate G1 which feeds a driver circuit G2, and its 14th (top) stage feeds a driver G3.

The outputs of G2 is normally low, and that of G3 is normally high; the output of driver G3 changes at count 8192, when U3 the final (14th) stage of U3 goes to 1, and the output of G2 changes a little later at count 9216.

The pulses generated across the triac TR1 when power is passing through the circuit are fed vid a diode D3 to a pair of 470 Q resistors R6 and R7 connected respectively to,a pair of light emitting diodes LED1 and LED2 as shown.

These two diodes produce green and red light respectively; they are physically so close together that they cannot be distinguished, so that their outputs are mixed together. Hence if LED1 alone is energized, the light output of the pair will be green; if both at energized1 the light output will be amber or yellow; and if LED2 alone is energized, the light output will be red. The two diodes together form the indicator 14.

The diodes LED1 and LED2 are also driven by the drivers G2 and G3 as shown. If the output of a driver is high, then the pulses generated by triac TRI and passing through diode D3 and resistor R6 or R7 pass through the LED and energize it. If the output of a driver is low, then the pulses from triac TR1 are prevented from energizing the LED. The "high" output of the drivers is in fact a floating (open collector) state; this means that the driver itself supplies no power to the LED (in the intervals between the pulses from the triac).

All outputs of the counter U3 are initially 0 (at count 0). As it counts up, so the outputs go to 1 in succession (and, of course, each time an output goes to i all preceding outputs go to 0 > . The final (14th) output is thus 0 until the count of 8192 is reached, when it goes to 1. The output of driver G3 is similarly low until that count is reached. LED2, which is red, is thus held off until, that count is reached1 when it goes on. The 11th and 14th outputs of U3 are fed to a NAND gate Go which feeds the driver G2 The 14th output is 0 until count 8192, and the 11th output goes to O as the 1,4th output goes to 1 and goes to 1 after a further 1024 counts.The output of gate G1 is 1 until both its inputs go to 0, i.e. until count 9216. The output of G2 is therefore also 1 until that count, holding the green diode LED1 on until that count.

Thus from counts 0 to 8192, green diode LED1 is on, giving a green light; from that count up to court 9216 the red diode LED2 ib on as well, giving an amber/yellow light; and from that count on, the green diode LED1 is off, giving a red light.

The output of gate G1 is also fed back to the count input of counter Ul via the AND gate G4. The count pulses from the triac TR1 are therefore prevented from passing through that gate as soon as the green LED goes out, so that the state of the system is then frozen. The system can be reset by operating a reset switch SW3 located at the bottom of the recess 15 (Fig. 1), which resets the counters U2 and U3.

The AND gate G4 is in fact merely a wired connection between resistor R3, the output of gate G1, and the count input of counter U1. Since the 1 output of gate G1 is floating, pulses from the triac TR1 can then pass to the count input of counter U1; the 0 output of gate Gi is held at 0, so preventing the pulses from passing to the count input of counter U1.

Switch SW2 is provided with an extreme position which is fed from gate G4.

This position is a test position. In this position, the pulses from the triac TR1 are fed directly to counter U3, instead of being divided down by counters U1 and U2, and the set period is thus 174 s (or, more precisely, 164 5 to amber yellow and 184 5 to red).

It will be realized that the two LEDs LED1 and LED2 can be physically separated, so that their states can be recognized even by a completely colour blind person.

It will also be realized that the switch SW2 may be made accessible without taking the casing apart. This would allow the user to set the desired period more easily.

With some types of electrical apparatus, the actual turning on of the apparatus makes a substantial contribution to its deterioration. It will be realized that the circuitry described can be modified to incorporate means for adding a suitable count increment into the acumulated count each time the asso- ciated apparatus is switched on, so that the total count represents a combination of the total time for which the apparatus has been on and the number of times which it has been switched on.

Claims (11)

C l a i m ts

1 A service interval indicator1 for connection to a device the service interval of which is to be measured, comprising counter means which count mains pulses while the device is energized, and signalling means operable at predetermined counts of the counter to give an indication when the counter reaches predetermined a count or counts.

2 An indicator according to claim 1 including a back-up battery to preserve the count in the counters if it is disconnected from the mains.

3 An indicator according to claim 1 wherein the counters are of a type the state of which is not lost on loss of power.

4 An indicator according to any previous claim wherein the predetermined count or counts is or are settable by means of internal setting means,

5 An indicator according to any previous claim wherein the signalling means comprise lighting elements.

6 An indicator according to claim 5 wherein the lighting elements comprise a red LED (light emitting diode) and a green LED in close juxtaposition and the counter means energizes the green LED up to a count slightly above the nominal service interval and the red LED from a count slightly below that interval.

7 An indicator according to sny previous claim directly mains powered and connected across the mains to the apparatus whose service interval is to be indicated.

8 An indicator according to any one of claims 1 to 6 connected in one of the mains supply lines to the apparatus whose service interval is to be indicated.

9 An indicator according to claim 8 incorporated in a connector1 such as an in-line connector, a plug and socket adaptor, or a plug, which is wired to the apparatus.

10 An indicator according to either of claims 8 and 9 including a triac with a zener diode and resistor connected in series across the triac and the triac gate connected to the junction of the zener diode and resistor such that pulses are developed across the triac, and the pulses are rectified to provide a power supply for the counting means.and also fed to the counting means to be counted.

11 A service interval indicator substantially as herein described.