GB2085167A - Temperature monitor for rotary component - Google Patents

Abstract

An electric induction motor has temperature sensors 34,36 in different zones of the rotor 12 which are connected to a transmitter 30 mounted on an end face of the motor shaft 14. The transmitter is energised through inductively linked windings 42,44 and has a light-emitting diode 38 which emits infrared or visible radiation which is received telemetrically by a photo- transistor receiver device 40 in line-of- sight relationship with the diode. Whichever sensor is hotter determines the frequency of the signal transmitted via diode 38, such frequency being incremented as the sensor output passes successive comparator thresholds, and corresponding lamps in the receiver being energised in response thereto. As a limiting temperature is reached and then exceeded a "limit approach" light and a "limit exceeded" light are illuminated. The components also detect whether the leads to the sensors are open or short circuited. <IMAGE>

Description

SPECIFICATION Temperature monitor The invention relates to temperature monitors.

It is known to monitor temperature in a rotating component by using a stationary detector sensitive to infra-red radiation emitted by the component.

Such a system suffers from the drawbacks that the detector can respond only to a zone of the compo next which is in direct line-of-sight relationship with the detector and such a zone is not generally precisely limited.

The invention enables the temperature of a relatively precisely limited zone of a rotating component to be monitored.

If desired more than one such zone of the same component may be monitored using a monitor according to the invention.

Atemperature monitor according to the invention installed in apparatus comprising a fixed component and a rotatable component comprises a transmitter and a receiver which are mounted on the rotatable and fixed components, respectively, and which include optical emitter and receiver devices positioned in line-of-sight relationship on the axis of rotation of the rotatable component, the transmitter comprising electric circuitry in which the emitter device is arranged to be energised from a winding carried by the rotating component and cooperating inductively with a second winding on the fixed component, the circuitry including a temperatureresponsive sensor which is mounted at a zone of the rotating component to be monitored and the output from which controls energisation of the emitter device, the receiver comprising electric circuitry in which the receiver device is arranged to control an electrical output which is fed to means to produce an indication of the temperature of said zone.

Preferably, the emitter and receiver device respectively emits, and responds to, electromagnetic radiation in the infra-red region. However, the invention includes the use of devices respectively emitting and receiving radiation in the visible region.

Preferably, the emitter device is a light-emitting diode (LED) and the receiver device is a phototransistor.

Preferably, the temperature-responsive sensor is a resistance-temperature detector. Alternatively, a thermo-couple or a thermistor may be used.

Monitors according to the invention are applicable especially, though not exclusively, to electric induction motors where the temperature of the cage of the motor is to be monitored.

If desired more than one temperature responsive sensor may be used, each at a respective zone to be monitored, with a diode arrangement included in the electric circuitry of the transmitter so that the sensor in the zone at the highesttemperaturewould dictate the indication given.

The invention includes apparatus having a temperature monitor.

The invention includes a transmitter and a receiver adapted for installation in apparatus as aforesaid to form a temperature monitor.

Two forms of monitor will now be described by way of example to illustrate the invention with reference to the accompanying drawings, in which: Figure 1 is a schematic longitudinal section through part of an electric induction motor having a temperature monitor; Figure 2 is a schematic diagram of a transmitter for use in a first form of monitor; Figure 3 is a schematic diagram of a receiver for use in the first form of monitor and of means producing an indication oftemperature; and Figures 4 & 5 are schematic diagrams similar to those of Figures 2 & 3 but showing a transmitter and a receiver respectively for use in a second form of monitor.

Figure 5 shows part of an electric induction motor of the kind having a stator 10 and a rotor 12. The stator 10 carries a winding (not shown) and the rotor 12 comprises a shaft 14 which carries a cage assembly and is supported in bearings, one of which is shown at 18 supported by a pedestal 20. The cage assembly includes sets of ring-shaped steel stampings 22 which carry copper alloy bars 24 located in slots in the stampings 22. The ends of the bars 24 are connected by copper alloy end rings, one of which is shown at 26.

Under certain conditions, such as stall conditions and excessively rapid repetition of starting, the temperature of the rotor 12 rises very rapidly. For example, the rotor bars 24 may reach a temperature of 300 Centigrade in less than 10 seconds in a stalled motor.

In order to provide for continuous monitoring of the temperature of the rotor 12, the motor has a temperature monitor comprising a transmitter 30; a receiver 32; one or more temperature responsive sensors 34, 36 forming part of electric circuitry 37 of the transmitter 30; optical emitter and receiver devices 38,40 respectively forming part of the electrical circuitry of the transmitter 30 and of the electric circuitry 39 of the receiver 32; and windings 42,44, respectively, carried by respective cylindrical aluminium housings 46,48, of the transmitter 30 and receiver 32, the windings 42, 44 cooperating inductively to transfer electric power in contactless fashion from the receiver 32 to the transmitter 30.

The temperature responsive sensor or each of them 34,36 is typically a nominal 100 ohm platinum resistance sensor and is connected by leads 50 or 52 to the circuitry 37 of the transmitter 30. The sensor 34 is located in one of the sets of rotorstampings 22.

The sensor 36 is located in an end-ring 26. The leads 50, or 52, pass through a radial bore 54 and a central axial bore 56 in the shaft 14 so as to pass the bearing 18.

The transmitter and receiver housings 46,48 are generally coaxial with one another and with the shaft 14. The receiver 32 is mounted on a support (not shown). The shaft 14 may typically for example have endwise movement or "float" of some + 10 millimetres (mm). The radial clearance between the housings 46,48 is typically some 3 mm with a tolerance of + 1 mm.

The emitter and receiver devices 38,40 are normally separated by some 12 mm. The emitter device 38 is a light-emitting diode (LED) typically for example a TIL 32 which emits infra-red light. The device 40 is typically a photo-transistor TIL 78 sensitive to infra-red light.

The transmitter housing 46 has typically an outside diameter of some 31/2 inches (90 mm) and a length of 11/2 inches (40 mm). The receiver housing 48 has an outside width and height of some 4 inches (100 mm), and a length of nearly 2 inches (50 mm).

The output from the receiver 32 passes via a cable 58 to an indicator (see Figure 3 or Figure 5).

The description given so far of the monitor is applicable generally by way of example to the broad features of construction, though the monitor may be designed to meet various requirements as further described below.

Where a relatively simple monitor is required it may be as shown in Figures 2 and 3. A more sophisticated form of the monitor is shown in Figures 4 and 5. Either form may be arranged on a motor as shown generally, for example, in Figure 1.

In both forms of monitor, the contactless signal link between the transmitter 30 and the receiver 32 is by way of telemetry, pulses of infra-red light being emitted by the emitter LED 38 and received by the photo-transistor 40, in line-of-sight relationship to the emitter 38.

In the monitor shown in Figures 2 and 3 the transmitter circuitry 37 (Figure 2) is such that a voltage across the resistance temperature sensor 34, say increases as the temperature of the sensor rises and all interference and spurious 50 Hz signals are removed from this voltage by a filter circuit 60. If this voltage continues to rise it will reach the pre-set threshold level of a comparator 'A', causing the output of that comparator to change state from a logic 1 to a logic 0. This, in turn, causes a step change in the base frequency of an oscillator 62. As the temperature continues to rise the voltage from the sensor 34 reaches the pre-set threshold level of a comparator 'B', causing the output to change state and producing a second step change in thefrequen- cy of the oscillator 62.

Athird comparator 'C' is a fail-safe device and is arranged to trip should the leads 50 to the sensor 34 short-circuit. The operation of comparator 'C' then inhibits the oscillator 62. Should the sensor leads 50 become open-circuit, both comparators 'A' and 'B' operate. The oscillator 62 drives the infra-red LED 38.

The transmitter circuitry is powered by a rectified and regulated voltage induced in the power coil 42.

By using a simple diode circuit (not shown) at the input stage a further sensor (such as the sensor 36 shown in Figure 1) can be monitored. The comparators would respond only to the sensor indicating the highest temperature.

In the monitor shown in Figures 1 and 2 the receiver circuitry 39 (Figure 3) is such that the output from the photo-transistor40 is applied to a comparator 66 with a raised threshold which in turn, triggers a monostable 68. The monostable pulse drives three re-triggerable monostable integrated circuit devices 70,72, 74 the time constants of which are arranged such that a logic '1' appears at the outputs if the pulse repetition rate at the inputs exceed a certain value. Conversely, a logic '0' appears at the outputs if the pulse repetition rate is below that value. The device 70 is set to trip if the input pulse repetition rate is equal to or greater than the base frequency of the transmitter oscillator.The device 72 is set to operate when the frequency of the transmitter oscillator 62 (Figure 2) increases owing to the influence of comparator 'A'. The device 74 is set to detect the change in frequency due to the operation of comparator 'B' of the transmitter (Figure 2).

The receiver circuitry 39 also includes an oscillator 80 which drives the power coil 44 via a power amplifier 82. The power coil 44 passes power to the~ transmitter circuitry 37 (Figure 2) by contactless inductive coupling (operating typically at 20 KHz) with the coil 42 as already mentioned.

The outputs from the devices 70,72 & 74 are passed via the multicore cable 58 (Figure 1) to an indicator which consists of a logic circuit 86 incorporating 4 Nand gates driving three warning lights 88,90, 92 and a relay 94.

Typically, the monitor as shown in Figures 2 and 3 is arranged so that the light 88 is illuminated indicating "system check" so long as the temperature of the zone of the rotor cage in which the sensor 34 is located remains below a predetermined level.

As the temperature in that zone increases to a value neartothe predetermined level, the light 90 will come on indicating "limit approach".

When that predetermined temperature level is exceeded in the zone, the light 92 comes on, indicating "limit exceeded". When that occurs the relay 94 closes its contact in response to which the power supply to the motor is cut off to protect the motor from excessive heating.

In the monitor as shown in Figures 3 and 4the transmitter circuitry 37 (Figure 3) is such that the resistance temperature sensor 34 say is supplied from a constant current source 100 and the voltage drop across the sensor varies linearly with temperature. Interference and spurious 50 Hz signals on the temperature signal are minimised by a filter circuit 102. The sensor voltage is fed into a fixed gain amplifier 104 which also incorporates a zero-offset circuit 106 such that a zero voltage output from the amplifier corresponds to 0 C at the sensor. The amplifier 104 drives a voltage - to - frequency convertor 108 which, in turn, supplies the LED 38 (Figure 1).

If a simple diode circuit (not shown) is incorporated at the input stage a further sensor such as the sensor 36 (Figure 1) can be monitored. The amplifier 104 would then only respond to the sensor with the largest output (i.e. the hottest sensor).

The transmitter is powered by a rectified and regulated voltage which is induced in power coils 42A, 42B (corresponding to the coil 42 as shown in Figure 1).

In the monitor as shown in Figures 4 and 5 the receiver circuitry 39 (Figure 5) is such that the output from the phototransistor 40 is applied to a comparator 120 with a raised threshold, which in turn, triggers a monostable 122.

An oscillator 124 drives the power coil 44 via a suitable power amplifier 126. The power coil 44 cooperates inductively with the coil 42 ofthetrans- mitter circuitry to form a contactless power link for the transmitter.

The pulse train from the monostable 122 is applied to a 4-decade counter l.C. 130 via a simple logic circuit and is used to gate pulses which are separately generated by a clock pulse generator 132. The system can be calibrated by varying the frequency of the clock pulse generator 132. The counter 130 drives a 4-decade, 7-segment, multiplexed display 134 using well established techniques. The counter 130 also has a multiplexed binary coded decimal output which is compared with the binary coded decimal output of a pre-set thumbwheel switch 136 using a 4-bit magnitude comparator l.C. 138.Using well-known techniques the "greater than" and "less than" outputs from the comparator 138 may be applied to a logic circuit 140, incorporating 4 NOR gates and 3 reset-set latches, which is arranged to de-multiplex the signals and control a warning light 142 and a relay 144to give a relay contact closure when the digital readout exceeds the setting of the thumbwheel switch (i.e. when the temperature of the sensor 34 exceeds the predetermined level).

Typically, for example, the monitor (whether as shown in Figures 1,2 & 3 or as modified with reference to Figures 4 & 5) responds to temperatures in the range 0 C to 300"C and is compatible with shaft speeds in the range 0 to 3000 revolutions per minute.

For the monitor as shown in Figures 2 and 3 the relay trip sensitivity is + 0.5 C, and for the form shown in Figures 4 and 5 it is + 1 digit. The accuracy in both cases is + 1% (equivalent to + 1 digit in the form shown in Figures 4 and 5).

In modifications (not shown) the infra-red emitter and receiver devices 38,40 may be replaced by devices operating in the visible light region. Instead of temperature resistance sensors, it is possible to use thermocouples or thermistors.

The monitor is applicable to machines other than motors.

Claims (13)

1. A temperature monitor installed in apparatus comprising a fixed component and a rotatable component, the monitor comprising a transmitter and a receiver which are mounted on the rotatable and fixed components, respectively, and which include optical emitter and receiver devices positioned in line-of-sight relationship on the axis of rotation of the rotatable component, the transmitter comprising electric circuitry in which the emitter device is arranged to be energised from a winding carried by the rotating component and cooperating inductively with a second winding on the fixed component, the circuitry including a temperatureresponsive sensor which is mounted at a zone of the rotating component to be monitored and the output from which controls energisation of the emitter device, the receiver comprising electric circuitry in which the receiver device is arranged to control an electrical output which is fed to means to produce an indication of the temperature of said zone.

2. A monitor according to claim 1, in which the emitter and receiver devices respectively emits, and responds to, electromagnetic radiation in the infrared region.

3. A monitor according to claim 1 or claim 2, in which the emitter device is a light-emitting diode and the receiver is a photo-transistor.

4. A monitor according to any preceding claim, in which more than one temperature responsive sensor is provided each at a respective zone of the apparatus to be monitored, the electric circuitry including an electronic arrangement so that zone at the highest temperature dictates the indication given.

5. A monitor according to any preceding claim, in which the transmitter is mounted on an end face of a shaft of a motor.

6. A transmitter and a receiver adapted for installation in apparatus in accordance with any preceding claim.

7. Apparatus having a temperature monitor in accordance with any preceding claim.

8. Atemperature monitor according to claim 1 substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.

9. A temperature monitor according to claim 1 substantially as hereinbefore described with reference to Figures 1, 4 and 5 of the accompanying drawings.

10. Atransmitterand a receiver according to claim 6 substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.

11. A transmitter and a receiver according to claim 6 substantially as herein before described with reference to Figures 1,4 and 5 of the accompanying drawings.

12. An electric motor according to claim 7, substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.

13. An electric motor according to claim 7, substantially as hereinbefore described with reference to Figures 1,4 and 5 of the accompanying drawings.