GB2142172A - Elapsed time and maintenance monitoring system - Google Patents

Abstract

An elapsed time and maintenance monitoring system for an electronic equipment system of the type having a plurality of sub-assemblies. The monitoring system comprises a respective solid state, non-volatile memory devices (10) installed in each sub-assembly of the equipment system for recording the required information. The memory devices (10) are coupled to a common central control unit (16) which supplies timing control, electrical power, and memory interrogation for the memory devices. The central control unit (16) detects when the equipment supply is switched off and sends control signals to all connected memory devices to cause updated utilisation data to be stored therein. <IMAGE>

Description

SPECIFICATION Elapsed time and maintenance monitoring system The present invention relates to elapsed time and maintenance monitoring systems for electronic equipment.

In connection with the maintenance of electrical and electronic equipment it is often desirable that records of utilisation and service history be kept.

This information can be used, for example, in reliability studies and for the scheduling of preventative maintenance. Records of other information may also be required, such as serial number, date or manufacture, build standard, fault conditions etc.

Electrical equipment is often built in modular form. One reason for this is to allow the replacement of faulty modules or sub-assemblies as a quick and easy initial repair procedure. A direct consequence of this is that separate records of utilisation and service information are required for each subassembly.

There is therefore a requirement for a system which will electrically monitor and record the utilisation and service history or each sub-assembly in an item of equipment and it is an objective of the present invention to provide such a system.

There exist elapsed time idicators (E.T.l's) which measure and display the total time that the equipment to which they are connected is switched on.

Electro-mechanical electro-chemical and solid state electronic types of ETI are available (see for example U.K. Patent No. 1 572 342). There also exist elapsed time recorders (E.T.R's) and elapsed time monitors (E.T.M's) which are solid state devices which totalise the equipment utilisation time in a non-volatile semiconductor memory. The elapsed time is read by temporary connection to a separate reader instrument. Versions of the above mentioned ETl's and ETR's are available which count the number of times they are energised.

Existing types of ETl's, ETR's and ETM's do not store any additional information and can only monitor the utilisation of one assembly or sub-assembly.

In accordance with the present invention in its broadest aspect, solid state, non-volatile memory devices are installed in each sub-assembly of an equipment system to record required information, these memory devices being coupled to a common central control unit which supplies timing control, power supply and memory interrogation for the various memory devices.

The respective memory devices will preferably remain within their associated sub-assemblies, so ensuring continuity of relevant service information in the situation where sub-assemblies may be interchanged.

Normally, in known systems, each memory device would have its own timing control circuits, power supply control circuits and memory interrogation circuits. These circuits form the largest part of any conventional solid state elapsed time measuring system. The combination of these functions in a central control unit allows a system to be produced with considerable savings in cost and size compared with a system having independent circuits in each sub-assembly.

Another major advantage is that the stored information from all the memory units can be displayed by the central control unit, without needing to switch the equipment off, or removing sub-assemblies to read their serial numbers.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of one embodiment of a system in accordance with the present invention; and Figure 2 is a flow diagram illustrating the operation of the system.

With reference to Figure 1, the illustrated system includes a plurality of memory units 10, each of which contains a memory circuit 12 of the electrically alterable read only memory type (E.A.R.O.M.) in which the contents of each addressable location, or word, can be electrically altered, independently. This is known as a word alterable EAROM. The EAROM in each memory unit 10 is arranged to store the elapsed time or event count information, together with the other service information required for each sub-assembly.

An interface circuit 14 in each memory unit transforms the information from the EAROM into serial data for transmission to a central control unit 16. The interface circuit 14 also controls the erase and write functions of the EAROM and updates the stored utilisation data as required.

The control unit 16 performs the following function: (a) provides regulated power supply to the memory units 10; (b) detects when the equipment supply is switched off and sends control signals to all the connected memory units 10 which cause the updated utilisation data to be stored into the EAROM 12; (c) provides power supply to the memory units 10 for a short time after the equipment power supply has been switched off in order to allow the data to be stored into the EAROM's 12; (d) provides an accurate timing signal to synchronise data transmission between the CCU 16 and the MU's 10; (e) the same timing signal may be used as a basis for the measurement of elapsed time by the MU's; (f) accepts control inputs from a read out unit 18 which select the required information from the various memory units; and (g) controls the transfer of information to and from the memory units 10 and interprets the required information for display on the read out unit 18.

The design of the memory units 10 can be kept as simple as possible by incorporating most of the system control functions into the CCU 16. A microprocessor or microcomputer based circuit can be used in the CCU 16 to perform many of these functions.

The implementation of this system requires interconnections between the central control unit 16 and the memory units 10 to be wired in the main frame or main interconnection system of the equipment.

The number of wires in the system interconnection bus 20 is therefore keptto a minimum.

In the system design shown in Figure 1, the serial data line 22 is connected sequentially between the memory units 10 in the form of interconnection know as a 'daisy chain'. With this type of interconnection, it can be arranged that after the first MU 10 has transmitted data to the CCU 16, the CCU 16 will send control signals which cause the first MU 10 to copy information to and from the second MU 1 0a in the chain. The first MU 10 will ignore all subsequent data and instructions until some speciai code is received. The CCU 16 can now read the second MU 10a and in turn, the subsequent MU's in the chain.

Equipment status and monitor signals 24 may be connected to the MU's 10 to allow the system to display on the read out unit 18 information about the present condition of the equipment.

The stored information in the EAROM's 12 can be divided into four categories: (a) Fixed information which is programmed into the EAROM 12 at the time of instaliation into the sub-assembly. This includes serial number and sub-assembly type number, etc.

(b) Control information which is also programmed into the EAROM 12 at the time of manufacture. This determines the mode of operation of the particular memory unit 10, for example timing resolution or event counting mode.

(c) Service information which may be updated occasionally during the operational life of the equipment, e.g. the time of the last overhaul.

(d) Variable information, such as the elapsed time, which must be updated each time the equipment is switched off.

Special techniques are required to maintain the integrity of information in the last of these categories. This is because this information must be read from the memory before being updated; the memory locations are then erased before the new information is re-written into the memory. The writing of this new information into memory must take place after the main equipment has been switched off and the monitor units 10 are being supplied from electrical energy stored in the CCU 16.

EAROM's require a relatively high supply current for several tens of milliseconds when data is being written into memory. For this reason it is disirable to minimise the amount of data which is written into memory each time the equipment is switched off.

The amount of data that is written governs the size of storage capacitor required in the CCU 16.

It is also necessary to ensure that the monitor unit's data will not be completely corrupted in the event of it becoming completely (or partially) disconnected from the CCU 16 while the equipment is switched on, or while the updated data is being written into the EAROM 12. Digital checking codes may also be stored, with the utilisation data, into the EAROM to allow corrupted data to be detected. It is therefore possible to test the validity of the data when the system is switched on, before the data is incremented or changed. If the data is valid it is copied into separate memory locations where it is stored as being the 'last known good data' (L.K.G.D.).

If an error is detected in the data at switch on, then the data stored in the LKGD locations may be substituted in place of the corrupted data. In this case the system will continue to work normally, but the utilisation during the previous period of energisation will not have been recorded.

The number of memory locations required to store the counter data and the check codes will depend on the maximum range and resolution of the elapsed time or event counter, and also on the number of bits in each memory location. Typically, four memory locations will be required for the counter data checking codes. For example, assuming a timing range of 99999 hours, with a resolution of 0.01 hours (seven decades) and four check bits, if the data is stored in binary coded decimal (B.C.D.) format then four locations of eight bits each are required in this example. This means that, typically, four successive memory write operations will be required in each MU 10, each time the equipment is switched off.

In one particular embodiment, however, only the low order data is written into the memory when the equipment is switched off, using the fact that the high order data will often remain unaltered between times of energisation. In this embodiment, the three least significant digits representing (99.9 hours range), plus the checking codes, can be considered to the low order data, which could be stored in only two eight bit words. The remaining data (multiples of tens of hours: four digits) can be considered as the high order data which is not normally re-written into the memory at switch off, unless a carry forward condition exists when the equipment is switched off.

If a carry forward condition is detected, the high order data only is written into the memory at switch off. This also requires only two eight bit words.

When the high order data is stored instead of the low order data, it can automatically be assumed that a carry has just occurred and that the low order data is therefore zero. This latter system of data storage reduces by a factor of two the number of write operations required and also the size of the storage capacitor required in the CCU.

Figure 2 shows a flow chart of the operation of a system incorporating the aforegoing features. In the system illustrated by Figure 2, the MU's 10 are designed to execute simple data manipulation on receipt of control codes from the CCU 16. This approach is intended to keep the MU design as simple as possible and means that all parts of the system are controlled directly by the CCU 16.

Alternative configurations of system are possible, using different partitioning of the circuit functions between the CCU and MU's and using different methods of interface.

Pseudo ROM may be used in place of EAROM.

This type of memory requires continuous power supply to retain the stored data, but the supply current is extremely low and can be supplied from small batteries or capacitors.

The memory units 10 may also be arranged to count electrical pulses generated by part of the equipment being monitored. In this case each memory unit 10 will operate as a non-volatile event counter within the same system.

Another possible extension of the system is the connection of a computer or data logger in place of the read-out unit 18. This would enable the utilisation and service information to be recorded automatically.

Claims (10)

1. An elapsed time and maintenance monitoring system for an electronic equipment system of the type having a plurality of sub-assemblies, the monitoring system comprising a respective solid state, non-volatile memory device installed in each said sub-assembly of the equipment system to record required information, the memory devices being coupled to a common central control unit which supplies timing control, electrical power, and memory interrogation for said memory devices.

2. A monitoring system as claimed in claim 1, wherein the central control unit is arranged to detect when the equipment supply is switched off and to send control signals to all connected memory devices which are arranged to then cause updated utilisation data to be stored therein.

3. A monitoring system as claimed in claim 1 or 2, wherein the central control unit provides regulated power supply to the memory devices of each sub-assembly during normal continuous operation of the equipment system and also provides power supply to said memory devices for a period after the equipment power supply has been switched off, in order to allow data to be stored in the memory devices at that time.

4. A monitoring system as claimed in claim 1,2 or 3 wherein the central control unit provides timing signals to synchronise data transmission between the central control unit and the memory devices.

5. A monitoring system as claimed in claim 4, wherein said timing signal is used by the memory devices as a basis for the measurement by said devices of elapsed time.

6. A monitory system as claimed in any of claims 1 to 5, including a read-out unit connected to the central control unit, the latter unit being adapted to accept control inputs from said read-out unit which select required information from said memory devices in the sub-assemblies.

7. A monitoring system as claimed in claim 6, wherein the central control unit controls the transfer of information to and from the memory devices and interprets the information provided thereby for display on the read-out unit.

8. A monitoring system as claimed in any of claims 1 to 7, wherein said memory devices are of the electrically alterable read only memory type (EAROM) in which each addressable location, or word, can be electrically altered, independently.

9. A monitoring system as claimed in claim 8, wherein each EAROM is arranged to store: (a) fixed information, such as serial number and sub-assembly type number, which is programmed into the EAROM at the time of installation of the associated sub-assembly; (b) control information which is programmed into the EAROM at the time of manufacture to determine the mode of operation of the relevant memory device; (c) service information, such as the time of last overhaul, which may be updated during the operational use of the equipment; and (d) variable information, such as elapsed time, which has to be updated each time the equipment is switched off.

10. An elapsed time and monitoring system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.