GB2145858A - Monitoring system - Google Patents

Abstract

A system for monitoring an engine operating in a hazardous area comprises an engine driven generator which supplies power which is rendered incapable of causing an ignition spark by circuits 16, 17 and the circuits 14, 15 include current limiters to protect circuits 16, 17 from voltage transients. The system also includes a tachometer 20, a speedometer 21, a set of sensors 51 to 55, 58, 59 a sensor checking circuit 30, and a set of comparators 32 responsive to the sensed variables to provide fault signals to a memory 34 formed from a set of magnetic relays which are associated with display elements to indicate faults. The comparators 32 also provide a signal to cause engine shutdown when a fault is detected to a drive circuit 36 of the main fuel valve solenoid 41. A system checking circuit 42 is provided which temporarily applies a signal indicative of a fault condition to the output of each sensor in turn and checks that each time such a signal is applied the output of the drive circuit 36 assumes a shutdown condition. <IMAGE>

Description

SPECIFICATION Monitoring system This invention relates to a monitoring system and particularly, but not exclusively, to a system for monitoring an engine operating in a hazardous area.

Underground mines sometimes contain combustible gas and diesel engined locomotives which operate in mines must be designed to a high safety standard so that there is no danger of such a locomotive causing an explosion. Present safety regulations require that such locomotives include a safety device to automatically stop the engine in the event of faults such as excessive engine coolant temperature. Present safety devices use either pressurized oil or compressed air but unfortunately such systems have poor reliability.

Areas such as mines which may contain combustible gas are classified as hazardous areas and electrical equipment operating in such areas must either by enclosed in flameproof containers or supplied with power from a barrier circuit which limits the voltage and current to levels below those at which an ignition spark can occur. In present mine locomotives, the safety requirement is met by enclosing the engine driven generator, headlamps, and headlamp switches in flameproof containers and by using no other electrical equipment.

The reliability of the engine safety devices could be improved by replacing the presently known devices with an electrically operating monitoring system. However, the design of such a monitoring system is difficult. One type of barrier circuit for hazardous areas comprises a zener diode and resistor connected in series between a pair of output terminals and a pair of input terminals which are connected across the zener diode through a fuse. The zener diode and resistor together limit the output voltage and current to safe levels and the fuse provides protection for the zener diode. For practical reasons, the electric generators used in mine locomotives have their nominal output voltage limited to 1 2 volts but in practice the output voltage is liable to high transients due to the absence of a battery.If such a generator is connected to a barrier circuit in which the zener voltage is greater than the transient voltage, a very high resistance must be used so as to limit the output current to a very low level and such a low level of current is insufficient to power a monitoring system. If the zener voltage is set to a level below the transient voltage, then it is very likely that the transients will blow the fuse and so this arrangement would not be useable. If a voltage regulator is positioned between the generator and the barrier circuit, then the voltage drop across the regulator circuit will reduce the available voltage to a level below that needed to power a monitoring system.

It is accordingly an object of this invention to provide a monitoring system for an engine operating in a hazardous area in which the above-mentioned problems are overcome.

According to this invention there is provided a system for monitoring an engine operating in a hazardous area comprising a prebarrier circuit for receiving power from an engine driven generator, said prebarrier circuit including current limiting means, a barrier circuit connected to receive power from the prebarrier circuit, and engine monitoring circuitry connected to receive power from the barrier circuit.

The current limiting means limits the current to a level below that which can cause damage to the barrier circuit and because the voltage drop across current limiting means is very small the current limiting means does not limit the available voltage to a level below that required by monitoring circuitry.

The current limiting means may comprise a transistor having its collector emitter path connected between an input and an output of the prebarrier circuit, at least one resistor connected between the emitter and said one input terminal, and voltage drop means connected between the base and said one input terminal.

A barrier circuit may comprise a resistor and zener diode connected in series, the zener diode being connected across the input of the circuit and the series circuit of the zener diode and the resistor being connected across the output.

The monitoring circuitry may include a set of sensors and fault detecting means responsive to the sensors. The fault detecting means may provide a signal for controlling engine shut down.

The monitoring circuitry may further include a set of magnetic relays driven by the fault detecting means and a set of display elements responsive to the outputs of the magnetic means. An auxiliary power supply may be provided for the display elements.

The fault detecting means may comprise two sets of comparators, each set of comparators including a comparator responsive to each of said sensor s, the outputs of the first set of comparators being combined to provide the shut down control signal, and the outputs of the second sets of comparators driving respective ones of said magnetic relays.

The monitoring circuitry may include a system checking arrangement, said arrangement comprising means for temporarily applying a signal representative of a fault condition to the output of each sensor in turn and means for checking that each time such a signal is applied to one of the sensors the shut down control signal assumes a shut down state.

In the preferred arrangement, the shut down control signal is connected to an input of a drive circuit for a solenoid operated fuel valve and the checking means is responsive to the output of the drive circuit.

The monitoring circuitry may include means responsive to each sensor for detecting the occurrence of an open circuit fault.

Where a monitoring system is used to monitor an apparatus under conditions where the power supply for the monitoring system is limited and where it is terminated after a fault has been detected which causes the apparatus to shut down, a problem occurs that the monitoring system may not be able to indicate which fault has caused shut down. It is accordingly another object of this invention to provide a monitoring system in which this problem is overcome.

According to another aspect of this invention there is provided a monitoring system comprising a set of sensor s, fault detecting means responsive to the sensors, a set of magnetic relays driven by the fault detecting means, and a set of display elements responsive to the outputs of the magnetic relays.

Magnetic relays provide the advantage that they can operate on very low currents and that they maintain their switched condition even after power is removed. Therefore such an arrangement can indicate which fault has caused shut down even where shut down terminates power supply to the monitoring system.

Where a monitoring system is used in conditions where high reliability is required, such a monitoring system should not only be capable of indicating a malfunction in the apparatus which it is monitoring but should also be capable of indicating a malfunction in itself. It is accordingly a further object of this invention to provide a monitoring system capable of indicating such a malfunction.

According to a further aspect of this invention there is provided a monitoring system comprising a set of sensors, fault detecting means responsive to the sensors providing a signal for controlling system shut down, a drive circuit for a solenoid operated element, said drive circuit having an input connected to the shut down control signal, and a system checking arrangement comprising means for temporarily applying a signal indicative of a fault condition to the output of each sensor in turn and means for checking that each time such a signal is applied to one of the sensors the output of the drive circuit assumes its shut down condition.

In this monitoring system, both faults which occur in the fault detecting means and faults which occur in the drive circuit will be detected.

This invention will now be described in more detail by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the general layout of a locomotive for operating in an underground mine; Figure 2 is a block diagram of a system for monitoring the diesel engine of a mine locomotive, the system being constructed in accordance with the present invention; Figure 3 is a circuit diagram of a barrier circuit and a prebarrier circuit which forms part of the monitoring system of Figure 2; Figure 4 is a block diagram of a tachometer circuit forming part of the monitoring system; Figures 5a and 5b are circuit diagrams of sensors forming part of the monitoring system:: Figure 6 is a circuit diagram of a solenoid drive circuit forming part of the monitoring system; Figure 7 is a circuit diagram of a sensor checking circuit forming part of the monitoring system; Figure 8 is a circuit diagram of two sets of comparators which form part of the monitoring system; Figure 9 is a circuit diagram of a memory and display circuit forming part of the monitoring system; and Figure 10 is a circuit diagram of a system checking circuit also forming part of the monitoring system.

Referring now to Figure 1, a locomotive for operating in an underground mine has a cab 10 for the driver at one or both ends and a diesel engine 11 for providing drive to the locomotive wheels and also for driving a nominal 1 2 volt electric generator 1 2. The generator 1 2 is enclosed in a flameproof housing 1 3. The generator 1 2 provides power to the locomotive lamps through cables which are enclosed in flameproof sheathing. Both the lamps and their switches are enclosed in flameproof containers and the switches are controlled with compressed air.

The system shown in Figure 2 monitors the diesel engine 11 and as will be described causes the engine to shut down if a fault occurs. In this sytem, the generator 1 2 provides power to a pair of prebarrier circuits 14 and 1 5 which in turn provide power to a pair of barrier circuits 1 6 and 1 7 and also serve to protect the circuits 1 6 and 1 7 from voltage transients from the generator 1 2. The output currents and voltages of the barrier circuits 16 and 1 7 are limited to levels below those which are capable of causing an ignition spark. The circuits 14 to 1 7 are mounted in a FLAME PROOF container so that any sparks which may inadvertently be generated in one of the circuits cannot cause an explosion and the circuits are connected to the generator 12 through a cable which is enclosed in a flameproof sheath. The FLAME PROOF container is mounted adjacent to the generator 1 2. It should be appreciated that neither the circuitry which is supplied with power from the barrier circuit 1 6 and 1 7 nor their associated cables need be enclosed in flameproof containers as the power supply to such circuitry is kept below that at which an ignition spark can occur.

The barrier circuit 1 6 supplies power through a pair of cables 18 and 1 9 to a tachometer circuit 20 and a speedometer circuit 21. The tachometer circuit 20 receives pulses from a variable reluctance transducer mounted on the output shaft of the diesel engine 11 and the speedometer 21 receives pulses from a variable reluctance transducer 23 driven by one of the locomotive wheels.

The tachometer 20 and speedometer 21 provide a display of engine speed and vehicle speed and also serve to detect overspeed conditions. Signals indicating overspeed conditions are supplied to a pair of opto isolators 24 and 25, the output signals from which are supplied respectively to a pair of cables 26 and 27 and 28 and 29. The opto isolators 24 and 25 serve to isolate electrically the circuitry supplied by barrier circuit 1 6 from that supplied by barrier circuit 1 7 so that there is no danger of the output powers of the two circuitries being added together. The tachometer 20, speedometer 21 and opto isolators 24 and 25 are mounted in one of the cabs 10. If it is desired to display vehicle and engine speed in the other cab 10, then a second tachometer 20 and second speedometer 21 may be provided.

The cables 26 and 27 and 28 and 29 are connected to a circuit 30 which also receives signals from engine parameter sensors S1 to S5 and S8 and Sg. The circuit 30 checks the signals from the sensors and also from the opto isolators 24 and 25 for open circuit faults and supplies output signals representing the various parameters which are sensed on a bus 31 to two sets of comparators 32. The comparators 32 detect fault conditions and provide signals on a bus 33 to a memory and display circuit 34. The comparators also provide a control signal SHUTDOWN on a rail 35 to a solenoid drive circuit 36, the signal SHUTDOWN assuming a low state when a fault is detected which requires engine shut down.The solenoid drive circuit 36 receives power through cables 37 and 38 from barrier circuit 1 7 and provides a drive signal via cables 39 and 40 to a solenoid operated fuel valve 41 which controls the fuel supply to the engine 11. The solenoid drive circuit 36 provides the power supply for the circuits 30, 32 and 34 and also for a system checking circuit 42. The circuit 42 supplies a set of signals on a bus 43 to the sensor checking circuit 30 for checking the operation of the monitoring system and receives a signal CHECK on a rail 44 from the solenoid drive circuit 36. The circuit 42 also supplies a signal CROWBAR to circuit 36 on a cable 45 and as will be described in more detail below this signal causes shut down if a system fault is detected.

The circuits 30, 32, 34, 36 and 42 are mounted in a dust and water proof container and may be encapsulated in black pigmented epoxy resin so as to render them tamper proof and the resulting assembly is mounted at a central position in the locomotive.

The various circuits shown in Figure 3 will now be described in more detail.

Referring now to Figure 3, the prebarrier circuit 14 has a pair of input terminals 50 and 51 and a pair of output terminals 52 and 53.

The input terminal 50 is connected through four parallel connected resistors R, to the emitter of a PNP transistor T1, the collector of which is connected to terminal 52. The terminal 50 is also connected through a pair of diodes D1 and D2 to the base of transistor T, and the base of transistor T1 is also connected through a resistor R2 to terminals 51 and 53.

The barrier circuit 1 6 has a pair of output terminals 54 and 55 connected respectively to cables 18 and 19. Terminal 52 is connected through a SObmA fuse F1 to a rail 56 which is connected through a 3.3ohm resistor R3 to terminal 54. Rail 56 is connected through a type BZY 93 zener diode ZD1 to terminal 55 and a further pair of zener diodes ZD2 and ZD3 are connected in parallel with zener diode ZD,. The zener diodes ZD,-ZD3 have a breakdown voltage of 7.5 volts and serves to limit the output voltage appearing at terminals 54 and 55 to this value and the resistor R3 limits the output current to 2.3A.

This combination of voltage and current is below that at which an ignition spark can occur. In the present arrangement, the zener diode ZD1 is operated in its breakdown state so that the full 7.5 volts are used but the current drawn is normally substantially less than 2.3A. The zener diodes ZD2 and ZD3 function if ZD1 fails and becomes open circuit and the fuse F1 protect zener diodes ZD1-ZD3 from damaging overcurrents.The transistor TI, resistors R1 and R2 and diodes D1 and D2 operate as a current limiter and serve to protect the fuse F1 from transient voltages from generator 1 3. In the absence of high or transient voltages, transistor T1 is operated in a saturated condition and so the voltage drop across this transistor is small and so has a negligible effect on the voltage available at terminals 54 and 55.

The prebarrier circuit 1 5 and barrier circuit 1 7 are generally similar to the circuits 14 and 1 6. However, in the barrier circuit 17, the fuse F1 is replaced by 250mA fuse, the zener diode ZD1-ZD3 are replaced by type BZY 93 zener diode having a breakdown voltage of 1 3 volts, and the resistor R3 is replaced by a 6ohm resistor. Also, in the prebarrier circuit 1 5 the resistors R1 are selected to provide protection for the 250mA fuse.

Referring to Figure 4 in the tachometer circuit 20, the output from transducer 22 is connected by a pair of rails 61 and 62 to the two inputs of an operational amplifier A1. A pair of diodes of opposing polarities and a resistor also connected across these two inputs. The non-inverting input is connected by a diode D3 to a OV rail which is connected to cable 19, the inverting input is connected through a resistor R4 to a 5V rail which is connected to cable 18, and the output of amplifier A1 is connected through a biasing resistor R5 to the 5V rail. The output of amplifier A1 is connected to the input of a pulse counting circuit 63, the output of which is connected to the non-inverting input of an operational amplifier A2 configured as an adjustable Low gain voltage follower. The amplifiers A1 and A2 each form one half of a type LM392 operational amplifier circuit.The output voltage of amplifier A2 is thus representative of engine speed and the output of this circuit is connected to the input of each of three type LM3914 bargraph generating circuits 64, 65 and 66. The bargraph generating circuits 64, 65 and 66 drive a set of light emitting diodes D4, each of which corresponds to a particular engine speed. The diodes D4 may be arranged in a row or circle and positioned where they may be easily viewed by the driver.

One of the outputs of bargraph circuit 66 corresponds to overspeed of engine 11 and this output is connected to rail 67. Consequently rail 67 goes low when overspeed occurs. In opto isolator 24, the 5V ral is connected through a pair of light emitting diodes D5, D6 to rail 67 and rail 67 is connected through a photodiode D7 and a resistor R6 to the OV rail. Diode D7 is optically coupled to diode D6 and so when rail 67 goes low both diodes D5 and D6 are latched into an energised state. Diode D5 is optically coupled to a photodiode D8 connected in parallel with a resistor R7 and output terminals 68 and 69.

Terminals 68 and 69 are connected to cables 26 and 27. Consequently, when overspeed is detected, the resistance between terminals 68 and 69 will fall.

Each of the sensors S1 to Ss and S8 and S9 shown in Figure 2 senses either pressure or temperature. An example of a temperature sensor is shown in Figure 5a an an example of a pressure sensor is shown in Figure 5b.

The temperature sensor comprises a thermistor R8 and resistor R9 connected between a pair of terminals 80, 81. The pressure sensor comprises a first pressure operated switch 82 connected between a pair of terminals 83 and 84, a second pressure operated switch 83 and a resistor R10 connected between terminals 83 and 84 and a resistor R" connected between terminals 83 and 84. Switch 83 is arranged to close before the pressure reaches a fault level and switch 82 is arranged to close at the fault level thereby providing two stage operation. Resistor R" is provided so that the sensor can be monitored for an open circuit fault.The solenoid drive circuit 36 shown in Figure 6 has a 12V rail 90 and a 0V rail 91 connected respectively to cables 38 and 37. Rail 90 is connected to the emitter of an NPN transistor T2, the collector of which is connected through a thyristor TH to rail 91.

The base of transistor T2 is connected through a resistor R15 to the collector of an NPN transistor T3, the emitter of which is connected to rail 91 and the emitter and collector of which are bridged by capacitor C1. The base of transistor T3 is connected through a resistor R16 to cable 35. The collector of transistor T2 and the OV rail are connected through cables 39 and 40 and a set of diodes D10 to the solenoid 41. The collector of transistor T2 is also connected through a resistor R17 and a light emitting diode D1l to the base of an NPN transistor T4, the collector of which is connected through a resistor R18 to the 12V rail 90, and also through a light emitting diode D,2 to the 0V rail, and the emitter of transistor T4 is connected directly to the DV rail.The collector of transistor T2 is further connected to the cable 44. Cable 45 is connected through a resistor Rl9 to the base of an NPN transistor T5, the collector of which is connected to cable 44 and the emitter of which is connected through a resistor R20 to the gate of thyristor TH. The gate of thyristor TH is connected to the OV rail through a capacitor C2. The circuit 36 also includes a voltage regulator 95 connected between rails 90 and 91 and which supplies a 5V rail 96 and a voltage regulator 97 connected between the collector of transistor T2 and the 0V rail and which provides a 5V power supply rail 98. The rails 96 and 98 are connected through a pair of diodes D14 and D1s, a resistor R21 and a 7 volt diac 99 to the gate of thyristor TH.Each of the regulators 95 and 97 comprises a type LM340 voltage regulator and the output of each of these regulators is bridged with a 1 microfarad capacitor.

If the signal CROWBAR is low and the signal SHUTDOWN is high, transistors T2 and T3 are turned on thereby supplying current to solenoid 41. If the signal SHUTDOWN goes low, transistors T2 and T2 will be turned off thereby removing the current supply to solenoid 41. However, current flow through solenoid 41 will be maintained by its self-inductance but under these conditions the signal CHECK will go low. If the signal SHUTDOWN is maintained in its low state, the current and solenoid 41 will eventually fall to zero causing shut down of the engine 11. Thus, if the signal SHUTDOWN goes low temporarily, this causes a signal CHECK to go low but does not cause engine shut down. If the signal CROW BAR goes high, the thyristor TH fires thereby removing the current supply permanently from solenoid 41 and causing engine shut down. Also, if the voltage on one of the supply rails 96 or 98 rises above 9 volts, diac 99 will conduct and this will also cause engine shut down.

The sensor checking circuit 30 shown in Figure 7 comprises ten pairs of terminals TM to To,,. The terminals TMx to TM5 are connected respectively to sensors S, to S5, the terminals TM6 and TM7 are connected respectively to the outputs of opto isolators 25 and 24 via cables 28 and 29 and 26 and 27, and terminals TM5 and TM9 are connected to sensors S8 and Sg. In the present example, the terminals T10 are not used.The sensors S1 to S5 respectively sense engine lubricant pressure, transmission oil temperature, exhaust gas temperature, engine coolant temperature, and transmission oil temperature. The sensors Ss and Sg respectively sense the air temperature delivered by an engine driven compressor and the temperature of brake components.

The pair of terminals TM1 comprises a positive terminal and a negative terminal. The positive terminal is connected through a pair of resistors R20 and R21 to the 5V rail 96 and the negative terminals is connected through a resistor R22 to the base of an NPN transistor T10. The emitter of this transistor is connected to the OV rail 91 and its collector is connected through a resistor R23 to the 5V rail 96. The collector is also connected through a diode D20 to a rail 109. The positive terminal is also connected to a rail 111 and in operation the voltage appearing on this rail represents engine lubricant pressure. The transistor T10 serves to detect an open circuit fault both in the cables which connect the terminals TM1 to sensor S1 and in the sensor itself. If such a fault occurs, transistor T10 is switched off thereby supplying a high signal to rail 109.

The circuit associated with each pair of terminals TM2 to TM10 is identical to that associated with terminals TM1 and so will not be described. The positive terminals of the pairs of terminals TM2 to TM10 are connected to rails 11 2 to 1 20. The rail 109 is connected through a resistor R24 to the base of an NPN transistor T", the collector of which is connected through a resistor R25 to the 5V rail 96 and the emitter of which is connected to the 0V rail. The collector of transistor T11 is also connected to a rail 121 and, in the event of an open circuit fault, the signal on this rail goes low.

The circuit 30 also provides a reference voltage for the comparators 32. In order to achieve this, the 5V rail 96 is connected through a pair of resistors R27 and R28 and a diode D21 to the OV rail 91. The resistor R26 and diode D21 are bridged by a capacitor C4.

The junction of resistors R27 and R28 is connected to the non-inverting input of an operational amplifier A3. The output of amplifier A3 is connected to the base of an NPN transistor T12, the collector of which is connected to the 5V rail 96 and the emitter of which is connected to a rail 1 30. The rail 1 30 is also connected to the non-inverting input of amplifier A3. In operation, a reference voltage of approximately 2.5 volts appears on rail 130.

The reference voltage is monitored and in order to achieve this the rail 1 30 is connected to the non-inverting input of an operational amplifier A4. The 5V rail 96 is connected through a pair of resistors R29 and R30 and a diode D21 to the OV rail and the junction of resistors R29 and R30 is connected to the inverting input of amplifier A4. Resistors R29 and R30 are chosen so that the output amplifier A4 goes low if there is a significant fall in the voltage on rail 1 30. The output of amplifier A4 is connected to a rail 1 22 and rail 1 22 is connected to the 5V rail through a further resistor R31. The amplifiers A3 and A4 each form one half of a type LM392 operational amplifier.The rails 111 to 1 22 together form the bus 31 which is connected to the comparators 32.

In circuit 30, the bus 43 from the system checking circuit 42 is connected through a set of resistors indicated at R32 to rails 111 to 1 20. In the circuit 32 as shown in Figure 8, rail 111 is connected through a resistor R40 to the positive input of a comparator CP1, the negative input of which is connected through a resistor R41 to the reference voltage rail 1 30. The output of comparator CP1 is connected to rail 35 and also through a resistor R42 to the 5V rail 96 and through a resistor R43 to its positive input. The resistors R20 and R21 shown in Figure 7 and the resistors associated with sensor S1 are chosen so that when the engine lubricant pressure falls to a value at which engine shut down should occur, the output of comparator CP1 goes low, thereby causing the signal SHUTDOWN on rail 35 to go low.The rails 11 2 and 1 22 are connected respectively to comparators CP2 to CP12 in a manner similar to that described for comparator CP1. If the voltage appearing on one of the rails 11 2 to 1 22 falls to a value at which shut down should occur, this will also cause the signal SHUTDOWN to go low. When the signal SHUTDOWN goes low as explained above, an engine shut down is caused. Subsequently, it is impossible to sustain engine running until the fault which has caused the shut down has been cleared.

The rail 111 is connected through a resistor R44 to the negative input of a comparator CP31. The 5V rail 96 is connected through a pair of resistors R45 and R46 and a diode D30 to the OV rail and the junction of resistors R45 and R46 is connected through resistor R47 to the positive input of comparator CP21 and through resistor R48 and D30 to the OV rail.

The output of comparator CP21 is connected through a resistor R49 to its positive input and also through resistor R50 to the 5V rail. Moreover, the output of comparator CP21 is connected to a rail 141. The resistors R45 to R45 function as a potential divider and supply a reference voltage to the positive input of comparators CP21. These resistors are selected so that the output of comparator CP21 goes high when the engine lubricant pressure falls to a value which is between its normal operational value and the value at which shut down must occur. Thus, a low signal on rail 1 41 provides an early warning that the engine lubricant pressure is falling to its shut down value and so gives an opportunity for the driver to take preventative action.

The rails 11 2 to 1 22 are associated with a set of comparators CP22 to CP32 and the connections associated with these comparators are similar to those associated with comparator CP21. The outputs of comparators CP22 to CP32 are connected to rails 142 to 1 52.

The resistors associated with comparators CP22 to CP25 and CP28 and CP29 are selected so that the outputs of these comparators go high before the parameter being sensed reaches its shut down value so as to give an early warning. In the case of comparators CP26 and CP27, this is not possible and the signals on rails 1 46 and 147 go low when overspeed occurs.

The rails 141 to 152 together form the bus 33 which is connected to the memory and display circuit 34.

In the memory and display circuit 34 shown in Figure 9, rail 141 is connected through a resistor R60 to the base of an NPN transistor T20, the emitter of which is connected to the OV rail 91 and the collector of which is connected through a relay coil W1 to the 5V rail 98. The collector of transistor T20 is also connected through a resistor R61 to the base of an NPN transistor T21, the emitter of which is connected to the OV rail 91 and the collector of which is connected through a relay coil W2 to the 5V rail 98. Both coils W1 and W2 are bridged by a pair of diodes. The relay coils W, and W2 form part of a magnetic latching relay which also includes relay contacts CT1.The relay contacts CT1 have a pole which is connected to the OV rail 91 and a pair of output contacts connected respectively to the base of transistor T21 and to a rail 1 60.

When the coil W2 is energised, the contacts latch in a position in which the OV rail 91 is connected to the base of transistor T21 and when the coil W1 is energised they are latched into a position in which the OV rail is connected to rail 1 60. The rail 1 60 is connected through a cable 161, a light emitting diode D41 and resistor R62 to a rail 1 62. The rail 1 62 is connected through a resistor R53 and a diode D33 to the 5V rail 56. In operation, if a low signal is present on rail 141, transistor T20 is off, transistor T21 is on, energising relay coil W2 until CT1 latches turning transistor T off. Light emitting diode D4, is not energised.

If the signal on rail 141 goes high, then transistor T20 is turned on, transistor T21 is turned off, relay coil W1 is energised thereby energising the light emitting diode D41.

iEach of the rails 1 42 to 1 52 is associated with a magnetic relay and the connections for these relays are the same as those described with reference to rail 141. The rails 142 to 1 52 are also connected to a set of light emitting diodes D42 to D52. The light emitting diodes D4, to D52 are positioned in one of the cabs 10 and together form a display for the driver.

The memory and display circuit 34 also includes an auxiliary power supply indicated at 1 70. In the auxiliary power supply 1 70, the 1 2V rail 90 is connected through a pair of resistors R65 and R56, and a diode D55 to a rail 1 71. The rail 1 71 is connected through a resistor R67, fuse F2 and a nickel cadmium battery 172 to the 0V rail 91. The resistor R67 is a current limiter for intrinsil safety purposes. The rail 171 is also connected through a push button switch 173 to rail 162. Under normal operating circumstances, the battery 1 72 is trickle charged. In the event of engine shut down, the normal power supply to rail 162 is removed. .However, under these circumstances the magnetic relay associated with the fault will be latched in its fault condition and so by depressing switch 1 73 the associated light emitting diode is energised thereby indicating the fault which has caused shut down. It is to be appreciated that the magnetic relays together provide a memory which is capable of operating at the low currents which are available in the present system and which maintain their latched condition even after the supply current has been removed.

The system checking circuit is shown in Figure 10 and includes a pair of type CD4017 decade counters 190 and 191, and a clock pulse generator 1 92. Each of the counters 1 90 and 1 91 has ten count outputs Q to Qg and each of these outputs goes high in turn in ascending numerical order in response to clock pulses. The clock pulse generator 192 is formed from a type 555 timer configured to give a clock period of 0.5S and a clock pulse is supplied to the CLOCK input of counter 1 90. The CLOCK INHIBIT input of counter 1 90 is connected to the 0V rail 91.

The Q3 output of counter 1 90 is connected to the CLOCK input of counter 1 91. The CLOCK INHIBIT and RESET inputs of counter 191 are connected to the OV rail 91. The O, to Q9 outputs of counter 1 91 are connected through respective resistors to the inputs of inverters 200 to 209, the outputs of which are connected by the bus 43 to the resistors R32 shown in Figure 7. The Q5 output of counter 1 90 is connected through a resistor to the input of an inverter 193, the output of which is connected through a resistor to the 5V rail 96. The output of inverter 1 93 is connected through respective resistors to the inputs of a set of inverters 210 to 219.The inverters 200 to 219 are type ULM2001 inverters. The outputs of the inverters 210 to 21 9 are connected respectively to the inputs of counters 200 to 209 and the outputs of inverters 210 to 219 are also connected through respective resistors to the OV rail 91. The Q7 output counter 1 90 is connected to cable 35 which provides the signal CROWBAR. The Q7 output of counter 1 90 is also connected through a resistor R70 to the base of an NPN transistor T30, the emitter of which is connected to the OV rail 91 and the collector of which is connected to rail 1 22 which, as shown in Figure 8, is connected through respective resistors to the positive inputs of comparators CP12 and CP32.The RESET input of counter 1 90 is connected to the collector of an NPN transistor T31, the emitter of which is connected to the 0V rail 91. The collector of transistor T31 is also connected through a resistor R72 to the 5V rail 96. The base of transistor T31 is connected through a resistor R33 to the 0V rail and through a further resistor R34 to rail 44 which receives the signal CHECK from the solenoid drive circuit 36.

During each normal cycle of operation, the counter 1 90 is initially reset. The count then advances and when the Q3 output goes high this causes counter 1 91 to advance. When the Q5 output of counter 1 90 goes high, this causes the output of inverter 1 93 to go low and so the outputs of inverters 210 to 219 go open circuit. Consequently, the output of the one of inverters 200 to 209 which is associated with a high output of counter 191 goes low and this causes the output of one of comparators CP, to CP10 to go low, thereby causing the signal SHUTDOWN to go low, and also one of comparators CP21 to CP30 to go high, thereby causing one of the light emitting diodes D4, to D60 to be energised temporarily.As a result of the signal SHUT DOWN going low, the signal CHECK goes low thereby resetting counter 1 90 and the cycle repeats.

However, if there is a fault in one of the comparators CP, to CP10 or in the solenoid drive circuit, the signal CHECK will not go low and so counter 1 90 is advanced until its Q7 output goes high. This causes the signal CROWBAR to go high thereby firing thyristor TH and causing shut down. A high signal on output Q7 will also cause a low signal on rail 1 22 thereby setting the magnetic relay associated with the comparator CP32 and in this way the origin of the fault which has caused shut down will be stored.

The overall operation of the system will now be described.

In order to start the engine, the solenoid 41 is mechanically held in its on position. After the engine has started, if a fault in the engine occurs, this will cause engine shut down. If a short circuit occurs in one of the sensors S, to S5 and S8 and S9 or in their associated leads, this will also cause a signal SHUTDOWN to go low and cause shut down. If an open circuit occurs in one of the sensors, this will be detected by comparator CP12 and cause a shut down. Also, as just explained, if a fault occurs in one of the comparators CP1 to CP10 or in the solenoid drive circuit, this will also cause shut down.After shut down has occurred, one of the magnetic relays shown in Figure 9 will be latched and by depressing button 1 73 the fault which caused the shut down can be detected. If one of the parameters monitored by sensors S, to S5 or S8 and Sg approaches a fault condition, the associated one of light emitting diodes D41 to D50 will be energised thereby providing an early warning. If a recovery is subsequently made, the light emitting diode is de-energised and shut down does not occur.

In a modification of the tachometer circuit shown in Figure 4, the rail 67 is connected to several outputs of bargraph generating circuits through a selector switch. The switch may then be operated so as to select the engine speed at which shut down occurs. A similar modification may be made to the speedometer circuit 21. Both the tachometer circuit 20 and the speedometer circuit 21 may also be modified so that shut down is caused when engine or vehicle acceleration or deceleration exceeds a predetermined rate.

Although the present invention has been described with reference to monitoring a diesel engine of a mine locomotive, the various aspects of the invention have a wider application. For example, the prebarrier circuit described in Figure 3 is suitable for use in any system for monitoring an engine operating in a hazardous area. The system checking circuit shown in Figure 10 is suitable for checking any monitoring system where a high degree of reliability is required and the arrangement of magnetic latching relay shown in Figure 9 is suitable for any monitoring system in which the power supply is removed after shut down has occurred.

Claims (16)

1. A system for monitoring an engine operating in a hazardcus area comprising a prebarrier circuit for receiving power from an engine driven generator, said prebarrier circuit including current limiting means, a barrier circuit connected to receive power from the prebarrier circuit, and engine monitoring circuitry connected to receive power from the barrier circuit.

2. A system as claimed in Claim 1 in which the current limiting means comprises a transistor having its collector emitter path connected between an input and an output of the prebarrier circuit, at least one resistor connected between the emitter and said one input terminal, and voltage drop means con nected between the base and said one input terminal.

3. A system as claims in claim 1 or claim 2 in which the barrier circuit comprises a resistor and zener diode connected in series, the zener diode being connected across the input of the circuit and the series circuit of the zener diode and the resistor being connected across the output.

4. A system as claimed in any one of the preceding claims in which monitoring circuitry includes a set of sensors and fault detecting means responsive to the sensors.

5. A system as claimed in Claim 4 in which the fault detecting means provides a signal for controlling engine shut down.

6. A sysem as claimed in Claim 5 in which the monitoring circuitry further includes a set of magnetic relays driven by the fault detecting means and a set of display elements responsive to the outputs of the magnetic relays.

7. A system as claimed in Claim 6 in which an auxiliary power supply is provided for the display elements.

8. A system as claimed in Claim 6 or Claim 7 in which the fault detecting means may comprise two sets of comparators, each set of comparators including a comparator responsive to each of said sensors, the outputs of the first set of comparators being combined to provide the shut down control signal, and the outputs of the second sets of comparators driving respective ones of said magnetic relays.

9. A system as claimed in any one of claims 5 to 8 in which the monitoring circuitry includes a system checking arrangement, said arrangement comprising means for temporarily applying a signal representative of a fault condition to the output of each sensor in turn and means for checking that each time such a signal is applied to one of the sensors the shut down control signal assumes a shut down state.

10. A system as claimed in claim 9 in which the shut down control signal is connected to an input of a drive circuit for a solenoid operated fuel valve and the checking means is responsive to the output of the drive circuit.

11. A system as claimed in any one of claims 4 to 10 in which the monitoring circuitry includes means responsive to each sensor for detecting the occurrence of an open circuit fault.

1 2. A monitoring system comprising a set of sensors, fault detecting means responsive to the sensors, a set of magnetic relays driven by the fault detecting means, and a set of display elements responsive to the outputs of the magnetic relays.

1 3. A monitoring system as claimed in Claim 1 2 in which an auxiliary power supply is provided for the display elements.

14. A monitoring system comprising a set of sensors, fault detecting means responsive to the sensors providing a signal for controlling system shut down, a drive circuit for a solenoid operated element, said drive circuit having an input connected to the shut down control signal, and a system checking arrangement comprising means for temporarily applying a signal indicative of a fault condition to the output of each sensor in turn and means for checking that each time such a signal is applied to one of the sensors the output of the drive circuit assumes its shut down condition.

1 5. A system as claimed in Claim 14 further including means responsive to each sensor for detecting the occurrences of an open circuit fault.

16. A monitoring system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.