CA1087277A - Telemetry system - Google Patents
Telemetry systemInfo
- Publication number
- CA1087277A CA1087277A CA258,174A CA258174A CA1087277A CA 1087277 A CA1087277 A CA 1087277A CA 258174 A CA258174 A CA 258174A CA 1087277 A CA1087277 A CA 1087277A
- Authority
- CA
- Canada
- Prior art keywords
- temperature
- voltage
- rotor
- signal
- converter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
- G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
- G01K7/18—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer
- G01K7/20—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer in a specially-adapted circuit, e.g. bridge circuit
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K1/00—Details of thermometers not specially adapted for particular types of thermometer
- G01K1/02—Means for indicating or recording specially adapted for thermometers
- G01K1/024—Means for indicating or recording specially adapted for thermometers for remote indication
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Arrangements For Transmission Of Measured Signals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A telemetry system for a dynamoelectric machine to detect temperature at a location on said rotor and to provide a signal externally giving an accurate indication of the temperature. A resistance temperature sensor (or resistance temperature detector) is connected to a constant current source and the voltage drop across it varies with changes in temperature. This voltage change is amplified and a voltage-to-frequency converter then provides a signal where frequency varies with the changes in temperature at the sensor. This signal is applied to slip rings on the rotor and brushes mounted on the stator conduct the signal to a frequency-to-voltage converter. A voltage-to-current converter then converts the signal to a current signal whose amplitude varies with changes in temperature at the sensor. This current signal is used for alarms or displays or controls. To provide power to the resistance temperature sensor and associated equipment i.e. the constant current source, the amplifier, and the voltage-to-frequency converter on the rotor, an external DC
supply is connected to the brushes and this is available on the slip rings. A filter and a DC to DC converter are connected to the slip rings and provide the necessary power to the sensor, amplifier and converter on the rotor. The rings and brushes provide a reliable direct connection between the equipment on the rotor and the external equipment, and the power for the rotor equipment and the temperature responsive signals are superimposed on the slip rings.
A telemetry system for a dynamoelectric machine to detect temperature at a location on said rotor and to provide a signal externally giving an accurate indication of the temperature. A resistance temperature sensor (or resistance temperature detector) is connected to a constant current source and the voltage drop across it varies with changes in temperature. This voltage change is amplified and a voltage-to-frequency converter then provides a signal where frequency varies with the changes in temperature at the sensor. This signal is applied to slip rings on the rotor and brushes mounted on the stator conduct the signal to a frequency-to-voltage converter. A voltage-to-current converter then converts the signal to a current signal whose amplitude varies with changes in temperature at the sensor. This current signal is used for alarms or displays or controls. To provide power to the resistance temperature sensor and associated equipment i.e. the constant current source, the amplifier, and the voltage-to-frequency converter on the rotor, an external DC
supply is connected to the brushes and this is available on the slip rings. A filter and a DC to DC converter are connected to the slip rings and provide the necessary power to the sensor, amplifier and converter on the rotor. The rings and brushes provide a reliable direct connection between the equipment on the rotor and the external equipment, and the power for the rotor equipment and the temperature responsive signals are superimposed on the slip rings.
Description
~V~72~ case 2492 This invention relates to a telemetry system, and in particular it relates to a ~ystem for providing at a remote point a sig~al representing a temperature on the rotor of a dynamoelectric machine, In dynamoelectric machines it is desirable to know the temperature at certain spot on the rotor.
This is particularly so in the larger rotating machines where, for example, a starting load or locked rotor may result in a rapid rise in temperature. N~ only can temperature information be used to actuate al~rms or protective devices, but it can be used to operate a machine more efficiently.
In the past, indications of temperature of the rotor of a dynamoelectric machine have been obtained indirectly and directly. One indirect scheme for obtaining temperature used an induction type relay and determined the stator inrush current during starting. This current drops off markedly as operating speed is approached. By selecting an induction type overcurrent relay with an inverse characteristic it is often possible to obtain a protective ~ystem that will permit a normal start but will trip if the motor stalls. This system approximates the heating of the rotor and trips when an indirectly determined temperature should have been reached. It takes no account of stored heat in the rotor from previous starts or from previous r~ning periods.
Another indirect scheme for approximating rotor temperature u~es a speed switch and an ass-ociated relaying system. If a predetermined ~peed is achieved in a predetermined time during starting, Caqe 2492 10~7277 the motor continue~ to run. If the predetermined speed is not achieved in this predetermined time, it is assumed the rotor temperature i~ excessive and the motor i8 shut down.
Other indirect systems have been developed for approximating rotor temperature, but they have not been ~ufficiently accurate and consequently they did not provide adequate protection or they were inefficient.
There were in the pa~t, two main schemes for obtaining a direct indication of the temperature of the rotor of a dynamoelectric machine. One of these schemes made use of a temperature detector on the rotor with leads brought to rotor slip rings.
Brushes which engaged the slip rings, and associated conductors, made the temperature signal available externally of the rotor. The temperature signal was thus conducted directly from the temperature detector to an external point where it could be amplified.
This scheme was not only direct but it was simple.
Unfortunately the temperature signal is very small and the ~ignal frequently became inaccurate because of the variability of the slip ring to brush contact.
In spite of its simplicity the scheme wa~ not popular, largely due to the poor quality and accuracy of the ; temperature signal.
In order to overcome the inaccuracies of the 31ip ring and brush system, a high frequency scheme using a rotary transformer was developed.
This arrangement provided a temperature responsive device on the rotor, normally at a hot spot on the rotor, together with an amplifier and an oscillator.
Case 2492 ~01~7277 The o~cillator was connected to a winding on the ahaft of a rotor and thi~ winding wa~ inductively coupled to an adjacent ~tator winding to form ~
rotary transformer. The oscillator frequency varied with temperature as detected by the temperature responsive device and consequently 3 signal repre-senting temperature wa~ available at the stationary winding of the rotary transformer. The temperature transmitting circuitry, that is the temperature responsive device, the amplifier and the oscillator, all required electrical power. This was provided by using another rotary transformer. The stator winding of thi~ second rotary transformer was connected to an oscillator (oscillating at a frequency different from that of the signal oscillator). The rotor winding was connected to a rectifier on the rotor which supplied power to the temperature tran-smitting circuitry. This arrangement provided adequate accuracy but the re]iability was considered to be less than that of the direct sy~tem using 81ip rings and brushes. Other direct arrangements were relatively complex and also were considered to be less reliable than a system using slip rings and brushes, It is therefore a feature of thi~ invention to provide an improved direct telemetry system for determining the temperature at a spot on the rotor and using slip rings and brushes to transmit the temperature signal from the rotor with satisfactory ac~uracy.
Very briefly, the telemetry system of this invention uses a resistance temperature sensor mounted Case 249~
1~87Z77 at an appropriate spot on the rotor. A constant current source supplies current to the temperature sensor, and an amplifier amplifies the signal from the temperature sensor representing the temperature.
In Canadian patent No. 962,088 - Boothman and Nutt, granted February 4, 1975 to the Canadian General Electric Company Limited, there is described an apparatus for measuring temperature on a stator winding using a resistance temperature sensor, a constant current source, and an amplifier. The present invention uses similar circuitry on the rotor to provide a signal representing temperature, and this signal is applied to a voltage-tofrequency converter.
The converter gives a signal whose frequency varies with temperature and this is transmitted over a pair of slip rings to a frequency~to-voltage converter and then to a voltage-to-current converter. The output from the voltage-to-current converter is a current whose value represents temperature. Because the signal transmitted over the lsip rings has been converted to a frequency variable signal and is not amplitude dependent, any changes in contact resistance or any stray voltages at the slip rings, will not affect the signal. In order to provide electrical power for the constant current source, amplifier and voltage-to-frequency converter on the rotor, the same slip rings are used to transmit DC power.
In other words the power to the rotor circuitry and the signal representing temperature from the rotor are superimposed. In one form of power supply a DC
voltage is applied to the slip rings and is passed through a filter when received by the rotor.
.
~ 4 ..~
1~7~ Ca~e 2492 It i~ then applied to a DC to DC converter which provides the necessary DC voltages for the rotor circuitry.
Thus, in accordance with the invention there is provided a telemetry system for use with a dynamoelectric machine h~ving a rotor ~nd a stator.
comprising temperature re.~ponsive means mounted on said rotor to sen3e temperature at a particu~ar location on said rotor and to provide a signal having a frequency which varies with changes in temperature at said location, slip rings mounted on said rotor with respective brushes mounted on said stator, a frequency responsive converter mean~ connected to said brushes to receive the variable frequency signal and to provide an output signal whose amplitude varies with said changes in temperature, a DC power source connected to said brushes to supply electrical power thereto, and means on said rotor connected to said slip rings to receive said electrical power and to provide a regulated DC power for said temperature respon~ive means, said power and said variable frequency signal being superimposed on said slip rings.
This invention will be described with reference to the accompanying drawings, in which : Figure 1 is a block schematic diagram of the circuitry of the invention, Figure 2 is a schematic diagram, partly in block form, which gives more information on a suitable circuit according to the invention, and Figure 3 is a simplified schematic diagram ~howing part of Figure 2 in more detail.
: , , r .
Case 2~92 ~7277 Referring first to Figure 1, a telemetry transmitter is represented by the block 10 formed with a broken line, and a telemetry converter is represented by the block 11 formed with a broken line.
The telemetry transmitter 10 comprises circuitry mounted on the rotor of a dynamoelectric machine (not shown) and is connected to slip rings 14 and 15 of the dynamoelectric machine. The telemetry converter 11 comprises circuitry external of the dynamoelectric machine and is connected to brushes (not shown) which engage the slip rings 14 and 15. A source of AC power 12 is connected with the telemetry converter 11.
For simplicity the circuit of Figure 1 is shown with blocks connected by single lines. It will be apparent to those skilled in the art that two paths are required for most interconnections and one path is frequently a common path such as a ground connection.
The telemetry transmitter 10 includes a temperature sensor 16 which is preferably a resistance temperature sensor or resistance temperature detector (RTD), that is a sensor having a resistance which hcanges with changes in temperature. A constant current ; source 17 provides a constant current for resistance temperature sensor 16. The temperature sensor 16 provides a signal where voltage changes with temperature and this is amplified by amplifier 18 and applied to a voltage-to-frequency converter 20. Voltage-to-frequency converter 20 provides a signal whose frequency varies with temperature and this signal is applied via capacitor 21 to slip ring 14.
' .
.
Case 2492 1~7277 In the telemetry converter 11, a capacitor 22 is electrically connected to slip ring 14 via a brush (not shown). The capacitor 22 isolates a frequency-to-voltage converter 23 from the DC on the slip ring 14 and passes the signal whose frequency varies with temperature to the frequency-to-voltage converter 23. The converter 23 provides a signal whose voltage varies with temperature and this is applied to a voltage-to-current converter 24, and the output from the converter 24, available at output 29, which is a current signal representing temperature, is used to control a display, alarm or protective device.
The electrical power for both the telemetry converter 11 and the telemetry transmitter 10 is derived from the AC source 12. A regulated DC supply 25 is connected to AC source 12 and it comprises a rectifier and regulator. It provides a regulated DC
to converters 23 and 24. A DC supply 26 is also connected to AC source 12. The DC supply 26 provides a DC voltage, which is ~iltered by filter 27 and applied to slip ring 14 for the telemetry transmitter.
The DC supply is passed through a filter 28 and is connected to a DC/DC converter 30 which provides a controlled DC voltage for amplifier 18 and converter 20. It also provides power for the constant current source 17.
It is believed the operation of the circuitry of Figure 1 is clear. In the telemetry converter 11 there is a source of DC power 25 and 26. The supply ,, 25 provides power for the circuitry of the telemetry ; ~ converter 11 and supply 26 is connected via slip ~087~ Case 2492 rinys 14 and 15 to provide power for telemetry transmitter 10 on the rotor. A resistance temperature sensor 16, or resistanc~ temperature detector (RTD) as it ha~ sometimes been called, provides a voltage sign~ whose amplitude changes as temperature changes, and this signal i~ amplified by amplifier 18 and converted to a variable frequency signal by converter 20. The variable frequency signal is ~uperimposed on the DC power and transmitted by the slip rings 14 and 15 to converters 23 and 24 which convert the variable frequency signal into a respective voltage varying signal and current varying signal. Thus, there i8 at output 29 a signal whose current changes as the temperature detected by the temperature sensor 16 changes.
Referring now to Figure 2, the slip rings 14 and 15, the temperature ~ensor 16, capacitors 21 and 22, and blocks 20, 23, 25 and 30 all bear the 8 ame designaltion numbers as in Figure 1. Cir~uitry representecl by other blocks in Figure 1 is shown more specifically in Figure 2.
In Figure 2 the resistance temperature sensor 16 receives a constant current from constant current source 17 which comprises an operational amplifier 32, a transistor 33 and a zener diode 34.
The operation of such a constant current source is well known. The noninverting input or + input of amplifier 32 i~ connected to the junction of zener diode 34 and resistance 35 to provide a reference voltage. The output of amplifier 32 is connected ~' to the junction of zener diode 34 and resistance 35 to provide a reference voltage. The output of 10~7Z77 Case ~492 amplifier 32 is connected to the base of transistor 33. A resistance 36 connects the emitter of transistor 33 to a positive voltage source, for example + 15 volts. A feedback resictance 37 connects the emitter of transistor 33 to the inverting or - input of operational amplifier 32. The collector of transistor 33 is connected by series resi~ters 38 and 40 to the re~istance temperature sensor (or RTD) 16, the other side of which is connected to ground. The operational amplifier 32, in response to a change in voltage at its inverting input caused by a change in current through resistance 36, controls transistor 33 to maintain a constant current. Thus, a constant current flows through resistances 36, 38, 40, and RTD 16 to ground.
The operation of resistance temperature sensor 16 (or RTD 16) is described in the afore-mentioned Canadian patent No. 962,088 however a brief description will be given with reference to Figure 3 to provide a complete description of the present invention, For simplicity the circuit shown in Figure 3 omits some capacities which are nor-mally used to bypass any transients to ground.
Figure 3 shows the temperature sens~ 16 in the form of a broken line block 16. The actual temperature sensitive element is shown as resistance 41. This temperature sensitive element 41 may be of copper or platinum or other suitable metal or alloy.
For example, a copper element may have a resistance of the order of 10 or 15 ohms and a platinum element may have a resistance of the order of 100 ohms.
A copper temperature sensitive element 41 may have _g_ Case 2492 ~087Z77 a resistance which changeq by perhaps 0.038 ohm~
per C, and consequently lead resistance could be significant. The leads have resistances shown in block 16 as RL. If it ia assumed a current I is flowing from the constant current source through the series path comprising resistancs 40, resistance RL
resistance element 41, resistance RL to ground. then the following equations apply:
VA = I ( R40 + R41 + 2 RL) (l) 10 VB = I (R41 + 2 RL) ( 2) VC ~ I ~ RL
where VA is the voltage at point A, Vg is the voltage at point B and Vc is the voltage at point C.
The other elements in the circuit of Figure 3 include an operational amplifier 42 with a feedback resistance 43 (i.e. R ), a resistance 47 connecting point A to the inverting input of amplifier 42 (having a value of 2 ), a resistance 44 connecting the lead from point C to the inverting input of amplifier 20 42 (resistance 44 has a value R), a resistance 45 connecting point B to the noninverting input of amplifier 42 (resistance 45 has a value R), and a resistance 46 connecting the noninverting input of amplifier 42 to ground (resistance 46 is selected to have a value equal to the resistance of 2R in parallel with RF) .
The output of operational amplifier 42 may be given as:
VOUT = RF ( 2Vg ~ VA - 2Vc) ~4) Substituting equations (1), (2) and (3~ in equation 4:
VouT = RF .I. (2R41 + 4RL - R40 - R41 - 2RL - 2RL~
. ~ ` ''- ~-, :
10~7~ Case 2492 = RF I (R41 - R40) (5) It will be seen that the lead resistance RL cancels out and does not affect the output of the operational amplifier 42. The current I is constant and the amplification RF of amplifier 42 is constant.
Therefore the output VOUT of amplifier 42 varies as the resistance of the temperature sensitive element 41.
The resistor 40 i~ included for convenience in calibration. If resistor 40 is selected to be equal to the resistance of temperature sensitive element 41 when it is at a reference temperature, for example zero C, then V0uT will be zero at th~t reference temperature (i.e. at 0C~, This simplifies calibration.
It i8 also convenient to have amplifier 42 provide an output which changes by an integral number for a change in temperature of 100C. Table I shows, by way of example, values used in one installation.
TEMP (C) R41 (ohms) VOUT (Volts) . . . _ 0 9.035 0 50 10.966 2 100 12.897 4 150 14.828 6 In the circuitry of the example referred to in connection with Table I, resistance 40 was selected to have a value of 9.035 ohms.
Referring now to Figure 2, a capacitance 49 is shown in parallel with feedback resistance 43.
Resistance 44 is shown in two portions to accommodate a by-pasæ capacitor 48. By-pass capacitors 50 ~nd 51 are also provided to by-pass transient voltages.
Case 2492 Because the voltage changes are relatively small it is desirable to eliminate transient voltages which would affect the output reading.
The output of operational amplifier 42 is connected to voltage-to-frequency converter 20 which may, for example, be a DATEL V/F converter, VFV-lOK.
This can be arranged to provide at its output 52 a series of negative voltage pulses whose frequency is 1000 times the input voltage. The converter 20 has connections 53 and 54 to a supply of positive and negative voltage, for example + 15 and -15 volts, from converter 30.
The output 52 of converter 20 is connected to the noninverting input of operational amplifier 55. Amplifier 55 is connected as a voltage follower to reduce output impedance. The output of operational amplifier 55 is connected through isolating capacitor 21 to slip ring 14, and thence through the associated brush (not shown) and isolating capacitor 22 to the inverting inE)ut of operational amplifier 56. A filter element comprising capacitor 57 and resistor 58 in parallel is connected from the inverting input of amplifier 56 to ground and conducts high frequencies to ground. The noninverting input of amplifier 56 is connected to the midpoint of resistors 60 and 61 which are connected in series between a source of positive voltage, say + 15 volts, and ground. Amplifier 56 acts as a biased comparator and reconstitutes the filtered waveform at its input into a square wave.
The output from amplifier or biased comparator 56 is applied to frequency-to-voltage converter '~ ' .
~7277 Case 2492 23~ This converter 23 may, for example, be a PHILBP~ICK 4702 F~V converter. The converter 23 is connected to supply 25 by conductors 62, 63 and 64 providing + 15,0 and -15 volts. A resi3tance network comprising resi~tors 65, 66 and 67 in series is conn-ected between conductors 62 and 64 and a variable tap on resistor 66 is connected by 3 conductor 68 to a "SUM" input on converter 23. The variable tap on resistor 66 sets the "zero" setting for converter 23, The gain of converter 23 is cont-rol]ed by a variable resistance 70 connected between the output of converter 23 and the "SUM"
input. Capacitor 71 is in parallel with resistance 70, The gain of converter 23 is conveniently set 80 that 6000 hertz, representing a temperature of 150C, will give a 10 volt output. That iq, the range of output is 0 to 10 volts for 0 to 150C.
The output of converter 23 is connected by a variable resistance 72 to the inverting input of operational amplifier 73, The noninverting input of amplifier 73 is connected to the mid-point of a pair of series resistances 74 and 75 connected from positive conductor 62 to ground. Resistance 75 is variable. The output of amplifier 73 is connected to the base of a transistor 76. The emitter of transistor 76 is connected to the positive conductor 62 by a resistance 77, and is connected to the in-verting input of amplifier 73 by a parallel com-bination of resistor 78 and capacitor 80. The inverting input of amplifier 73 is connected to ground by resistance 81, The collector of transistor 76 is connected to ground by a series path comprising . ~
Case 2492 -1~87Z77 resistance 82 and load 83. The amplifier 73 and transistor 76 form a voltage-to-current converter whose gain is controlled by variable resistance 72 and whose zero level is controlled by variable resistance 75.
Table II below shows the figures for the previous Table I extended to show the output.
TEMP R41 VOUT Freq. V-Convert 23 OUTPUT
( C) (ohms) (volts) _hertz) (volts) (ma) 0 9.035 o 0 0 4.0 10.966 2 2000 3.33 9.33 100 12.897 4 4000 6.66 14.66 150 14.828 6 6000 10.0 20.0 The telemetry converter llreceives its power from a regulated DC supply 25 which may, for example, be a BURR BROWN 552 power supply providing + 15 -volts, 0 and -15 volts on conductors 62, 63 and 64 as was previously mentioned. A transformer 84, con-nected to AC supply 12, provides a voltage for bridge rectifier having diodes 85 and a capacitor 86. This is DC supply 26 (Figure 1). The positive output of the bridge rectifier is connected by conductor 87 to a choke 88 to the brush and slip ring 14. The diode 90 is provided to dissipate over voltage if - the connections should be broken when the power ' is on. A diode 91 is connected to the ring 14 for protection against a reversal of connection to the brushes or slip rings 14 and 15. The power from slip ring 14 is again filtered by choke 92, protected as before by diode 93 against over voltage which could result from disconnection with voltage applied.
The choke 93 is connected to a pre-regulator 94 ~ 14 - . ~ - ' :
,., . ~ . . .
lQ~372~ Case 2492 which reduce~ the unregulated DC voltage to 24 volt~
DC ~uitable for DC to DC converter 30. A filter capacitor 95 is connected between choke 92 and pre-regulator 94 to ground.
The DC to DC converter 30 may, for example.
be a BH Industries 2055-24-15 converter which provide~
+ and -15 volts on conductors 53 and 54.
It is believed the operation of Figure 2 will now be clear and no further description i~
required.
The telemetry system provides a reliable transfer of a temperature signal from a rotor of a dynamoelectric machine by direct contact over slip rings and brushes. Changes in resistance between 81ip rings and brushes, or radio frequency inter-ference, will not affect the accuracy of the trans-mission of temperature signals.
This is particularly so in the larger rotating machines where, for example, a starting load or locked rotor may result in a rapid rise in temperature. N~ only can temperature information be used to actuate al~rms or protective devices, but it can be used to operate a machine more efficiently.
In the past, indications of temperature of the rotor of a dynamoelectric machine have been obtained indirectly and directly. One indirect scheme for obtaining temperature used an induction type relay and determined the stator inrush current during starting. This current drops off markedly as operating speed is approached. By selecting an induction type overcurrent relay with an inverse characteristic it is often possible to obtain a protective ~ystem that will permit a normal start but will trip if the motor stalls. This system approximates the heating of the rotor and trips when an indirectly determined temperature should have been reached. It takes no account of stored heat in the rotor from previous starts or from previous r~ning periods.
Another indirect scheme for approximating rotor temperature u~es a speed switch and an ass-ociated relaying system. If a predetermined ~peed is achieved in a predetermined time during starting, Caqe 2492 10~7277 the motor continue~ to run. If the predetermined speed is not achieved in this predetermined time, it is assumed the rotor temperature i~ excessive and the motor i8 shut down.
Other indirect systems have been developed for approximating rotor temperature, but they have not been ~ufficiently accurate and consequently they did not provide adequate protection or they were inefficient.
There were in the pa~t, two main schemes for obtaining a direct indication of the temperature of the rotor of a dynamoelectric machine. One of these schemes made use of a temperature detector on the rotor with leads brought to rotor slip rings.
Brushes which engaged the slip rings, and associated conductors, made the temperature signal available externally of the rotor. The temperature signal was thus conducted directly from the temperature detector to an external point where it could be amplified.
This scheme was not only direct but it was simple.
Unfortunately the temperature signal is very small and the ~ignal frequently became inaccurate because of the variability of the slip ring to brush contact.
In spite of its simplicity the scheme wa~ not popular, largely due to the poor quality and accuracy of the ; temperature signal.
In order to overcome the inaccuracies of the 31ip ring and brush system, a high frequency scheme using a rotary transformer was developed.
This arrangement provided a temperature responsive device on the rotor, normally at a hot spot on the rotor, together with an amplifier and an oscillator.
Case 2492 ~01~7277 The o~cillator was connected to a winding on the ahaft of a rotor and thi~ winding wa~ inductively coupled to an adjacent ~tator winding to form ~
rotary transformer. The oscillator frequency varied with temperature as detected by the temperature responsive device and consequently 3 signal repre-senting temperature wa~ available at the stationary winding of the rotary transformer. The temperature transmitting circuitry, that is the temperature responsive device, the amplifier and the oscillator, all required electrical power. This was provided by using another rotary transformer. The stator winding of thi~ second rotary transformer was connected to an oscillator (oscillating at a frequency different from that of the signal oscillator). The rotor winding was connected to a rectifier on the rotor which supplied power to the temperature tran-smitting circuitry. This arrangement provided adequate accuracy but the re]iability was considered to be less than that of the direct sy~tem using 81ip rings and brushes. Other direct arrangements were relatively complex and also were considered to be less reliable than a system using slip rings and brushes, It is therefore a feature of thi~ invention to provide an improved direct telemetry system for determining the temperature at a spot on the rotor and using slip rings and brushes to transmit the temperature signal from the rotor with satisfactory ac~uracy.
Very briefly, the telemetry system of this invention uses a resistance temperature sensor mounted Case 249~
1~87Z77 at an appropriate spot on the rotor. A constant current source supplies current to the temperature sensor, and an amplifier amplifies the signal from the temperature sensor representing the temperature.
In Canadian patent No. 962,088 - Boothman and Nutt, granted February 4, 1975 to the Canadian General Electric Company Limited, there is described an apparatus for measuring temperature on a stator winding using a resistance temperature sensor, a constant current source, and an amplifier. The present invention uses similar circuitry on the rotor to provide a signal representing temperature, and this signal is applied to a voltage-tofrequency converter.
The converter gives a signal whose frequency varies with temperature and this is transmitted over a pair of slip rings to a frequency~to-voltage converter and then to a voltage-to-current converter. The output from the voltage-to-current converter is a current whose value represents temperature. Because the signal transmitted over the lsip rings has been converted to a frequency variable signal and is not amplitude dependent, any changes in contact resistance or any stray voltages at the slip rings, will not affect the signal. In order to provide electrical power for the constant current source, amplifier and voltage-to-frequency converter on the rotor, the same slip rings are used to transmit DC power.
In other words the power to the rotor circuitry and the signal representing temperature from the rotor are superimposed. In one form of power supply a DC
voltage is applied to the slip rings and is passed through a filter when received by the rotor.
.
~ 4 ..~
1~7~ Ca~e 2492 It i~ then applied to a DC to DC converter which provides the necessary DC voltages for the rotor circuitry.
Thus, in accordance with the invention there is provided a telemetry system for use with a dynamoelectric machine h~ving a rotor ~nd a stator.
comprising temperature re.~ponsive means mounted on said rotor to sen3e temperature at a particu~ar location on said rotor and to provide a signal having a frequency which varies with changes in temperature at said location, slip rings mounted on said rotor with respective brushes mounted on said stator, a frequency responsive converter mean~ connected to said brushes to receive the variable frequency signal and to provide an output signal whose amplitude varies with said changes in temperature, a DC power source connected to said brushes to supply electrical power thereto, and means on said rotor connected to said slip rings to receive said electrical power and to provide a regulated DC power for said temperature respon~ive means, said power and said variable frequency signal being superimposed on said slip rings.
This invention will be described with reference to the accompanying drawings, in which : Figure 1 is a block schematic diagram of the circuitry of the invention, Figure 2 is a schematic diagram, partly in block form, which gives more information on a suitable circuit according to the invention, and Figure 3 is a simplified schematic diagram ~howing part of Figure 2 in more detail.
: , , r .
Case 2~92 ~7277 Referring first to Figure 1, a telemetry transmitter is represented by the block 10 formed with a broken line, and a telemetry converter is represented by the block 11 formed with a broken line.
The telemetry transmitter 10 comprises circuitry mounted on the rotor of a dynamoelectric machine (not shown) and is connected to slip rings 14 and 15 of the dynamoelectric machine. The telemetry converter 11 comprises circuitry external of the dynamoelectric machine and is connected to brushes (not shown) which engage the slip rings 14 and 15. A source of AC power 12 is connected with the telemetry converter 11.
For simplicity the circuit of Figure 1 is shown with blocks connected by single lines. It will be apparent to those skilled in the art that two paths are required for most interconnections and one path is frequently a common path such as a ground connection.
The telemetry transmitter 10 includes a temperature sensor 16 which is preferably a resistance temperature sensor or resistance temperature detector (RTD), that is a sensor having a resistance which hcanges with changes in temperature. A constant current ; source 17 provides a constant current for resistance temperature sensor 16. The temperature sensor 16 provides a signal where voltage changes with temperature and this is amplified by amplifier 18 and applied to a voltage-to-frequency converter 20. Voltage-to-frequency converter 20 provides a signal whose frequency varies with temperature and this signal is applied via capacitor 21 to slip ring 14.
' .
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Case 2492 1~7277 In the telemetry converter 11, a capacitor 22 is electrically connected to slip ring 14 via a brush (not shown). The capacitor 22 isolates a frequency-to-voltage converter 23 from the DC on the slip ring 14 and passes the signal whose frequency varies with temperature to the frequency-to-voltage converter 23. The converter 23 provides a signal whose voltage varies with temperature and this is applied to a voltage-to-current converter 24, and the output from the converter 24, available at output 29, which is a current signal representing temperature, is used to control a display, alarm or protective device.
The electrical power for both the telemetry converter 11 and the telemetry transmitter 10 is derived from the AC source 12. A regulated DC supply 25 is connected to AC source 12 and it comprises a rectifier and regulator. It provides a regulated DC
to converters 23 and 24. A DC supply 26 is also connected to AC source 12. The DC supply 26 provides a DC voltage, which is ~iltered by filter 27 and applied to slip ring 14 for the telemetry transmitter.
The DC supply is passed through a filter 28 and is connected to a DC/DC converter 30 which provides a controlled DC voltage for amplifier 18 and converter 20. It also provides power for the constant current source 17.
It is believed the operation of the circuitry of Figure 1 is clear. In the telemetry converter 11 there is a source of DC power 25 and 26. The supply ,, 25 provides power for the circuitry of the telemetry ; ~ converter 11 and supply 26 is connected via slip ~087~ Case 2492 rinys 14 and 15 to provide power for telemetry transmitter 10 on the rotor. A resistance temperature sensor 16, or resistanc~ temperature detector (RTD) as it ha~ sometimes been called, provides a voltage sign~ whose amplitude changes as temperature changes, and this signal i~ amplified by amplifier 18 and converted to a variable frequency signal by converter 20. The variable frequency signal is ~uperimposed on the DC power and transmitted by the slip rings 14 and 15 to converters 23 and 24 which convert the variable frequency signal into a respective voltage varying signal and current varying signal. Thus, there i8 at output 29 a signal whose current changes as the temperature detected by the temperature sensor 16 changes.
Referring now to Figure 2, the slip rings 14 and 15, the temperature ~ensor 16, capacitors 21 and 22, and blocks 20, 23, 25 and 30 all bear the 8 ame designaltion numbers as in Figure 1. Cir~uitry representecl by other blocks in Figure 1 is shown more specifically in Figure 2.
In Figure 2 the resistance temperature sensor 16 receives a constant current from constant current source 17 which comprises an operational amplifier 32, a transistor 33 and a zener diode 34.
The operation of such a constant current source is well known. The noninverting input or + input of amplifier 32 i~ connected to the junction of zener diode 34 and resistance 35 to provide a reference voltage. The output of amplifier 32 is connected ~' to the junction of zener diode 34 and resistance 35 to provide a reference voltage. The output of 10~7Z77 Case ~492 amplifier 32 is connected to the base of transistor 33. A resistance 36 connects the emitter of transistor 33 to a positive voltage source, for example + 15 volts. A feedback resictance 37 connects the emitter of transistor 33 to the inverting or - input of operational amplifier 32. The collector of transistor 33 is connected by series resi~ters 38 and 40 to the re~istance temperature sensor (or RTD) 16, the other side of which is connected to ground. The operational amplifier 32, in response to a change in voltage at its inverting input caused by a change in current through resistance 36, controls transistor 33 to maintain a constant current. Thus, a constant current flows through resistances 36, 38, 40, and RTD 16 to ground.
The operation of resistance temperature sensor 16 (or RTD 16) is described in the afore-mentioned Canadian patent No. 962,088 however a brief description will be given with reference to Figure 3 to provide a complete description of the present invention, For simplicity the circuit shown in Figure 3 omits some capacities which are nor-mally used to bypass any transients to ground.
Figure 3 shows the temperature sens~ 16 in the form of a broken line block 16. The actual temperature sensitive element is shown as resistance 41. This temperature sensitive element 41 may be of copper or platinum or other suitable metal or alloy.
For example, a copper element may have a resistance of the order of 10 or 15 ohms and a platinum element may have a resistance of the order of 100 ohms.
A copper temperature sensitive element 41 may have _g_ Case 2492 ~087Z77 a resistance which changeq by perhaps 0.038 ohm~
per C, and consequently lead resistance could be significant. The leads have resistances shown in block 16 as RL. If it ia assumed a current I is flowing from the constant current source through the series path comprising resistancs 40, resistance RL
resistance element 41, resistance RL to ground. then the following equations apply:
VA = I ( R40 + R41 + 2 RL) (l) 10 VB = I (R41 + 2 RL) ( 2) VC ~ I ~ RL
where VA is the voltage at point A, Vg is the voltage at point B and Vc is the voltage at point C.
The other elements in the circuit of Figure 3 include an operational amplifier 42 with a feedback resistance 43 (i.e. R ), a resistance 47 connecting point A to the inverting input of amplifier 42 (having a value of 2 ), a resistance 44 connecting the lead from point C to the inverting input of amplifier 20 42 (resistance 44 has a value R), a resistance 45 connecting point B to the noninverting input of amplifier 42 (resistance 45 has a value R), and a resistance 46 connecting the noninverting input of amplifier 42 to ground (resistance 46 is selected to have a value equal to the resistance of 2R in parallel with RF) .
The output of operational amplifier 42 may be given as:
VOUT = RF ( 2Vg ~ VA - 2Vc) ~4) Substituting equations (1), (2) and (3~ in equation 4:
VouT = RF .I. (2R41 + 4RL - R40 - R41 - 2RL - 2RL~
. ~ ` ''- ~-, :
10~7~ Case 2492 = RF I (R41 - R40) (5) It will be seen that the lead resistance RL cancels out and does not affect the output of the operational amplifier 42. The current I is constant and the amplification RF of amplifier 42 is constant.
Therefore the output VOUT of amplifier 42 varies as the resistance of the temperature sensitive element 41.
The resistor 40 i~ included for convenience in calibration. If resistor 40 is selected to be equal to the resistance of temperature sensitive element 41 when it is at a reference temperature, for example zero C, then V0uT will be zero at th~t reference temperature (i.e. at 0C~, This simplifies calibration.
It i8 also convenient to have amplifier 42 provide an output which changes by an integral number for a change in temperature of 100C. Table I shows, by way of example, values used in one installation.
TEMP (C) R41 (ohms) VOUT (Volts) . . . _ 0 9.035 0 50 10.966 2 100 12.897 4 150 14.828 6 In the circuitry of the example referred to in connection with Table I, resistance 40 was selected to have a value of 9.035 ohms.
Referring now to Figure 2, a capacitance 49 is shown in parallel with feedback resistance 43.
Resistance 44 is shown in two portions to accommodate a by-pasæ capacitor 48. By-pass capacitors 50 ~nd 51 are also provided to by-pass transient voltages.
Case 2492 Because the voltage changes are relatively small it is desirable to eliminate transient voltages which would affect the output reading.
The output of operational amplifier 42 is connected to voltage-to-frequency converter 20 which may, for example, be a DATEL V/F converter, VFV-lOK.
This can be arranged to provide at its output 52 a series of negative voltage pulses whose frequency is 1000 times the input voltage. The converter 20 has connections 53 and 54 to a supply of positive and negative voltage, for example + 15 and -15 volts, from converter 30.
The output 52 of converter 20 is connected to the noninverting input of operational amplifier 55. Amplifier 55 is connected as a voltage follower to reduce output impedance. The output of operational amplifier 55 is connected through isolating capacitor 21 to slip ring 14, and thence through the associated brush (not shown) and isolating capacitor 22 to the inverting inE)ut of operational amplifier 56. A filter element comprising capacitor 57 and resistor 58 in parallel is connected from the inverting input of amplifier 56 to ground and conducts high frequencies to ground. The noninverting input of amplifier 56 is connected to the midpoint of resistors 60 and 61 which are connected in series between a source of positive voltage, say + 15 volts, and ground. Amplifier 56 acts as a biased comparator and reconstitutes the filtered waveform at its input into a square wave.
The output from amplifier or biased comparator 56 is applied to frequency-to-voltage converter '~ ' .
~7277 Case 2492 23~ This converter 23 may, for example, be a PHILBP~ICK 4702 F~V converter. The converter 23 is connected to supply 25 by conductors 62, 63 and 64 providing + 15,0 and -15 volts. A resi3tance network comprising resi~tors 65, 66 and 67 in series is conn-ected between conductors 62 and 64 and a variable tap on resistor 66 is connected by 3 conductor 68 to a "SUM" input on converter 23. The variable tap on resistor 66 sets the "zero" setting for converter 23, The gain of converter 23 is cont-rol]ed by a variable resistance 70 connected between the output of converter 23 and the "SUM"
input. Capacitor 71 is in parallel with resistance 70, The gain of converter 23 is conveniently set 80 that 6000 hertz, representing a temperature of 150C, will give a 10 volt output. That iq, the range of output is 0 to 10 volts for 0 to 150C.
The output of converter 23 is connected by a variable resistance 72 to the inverting input of operational amplifier 73, The noninverting input of amplifier 73 is connected to the mid-point of a pair of series resistances 74 and 75 connected from positive conductor 62 to ground. Resistance 75 is variable. The output of amplifier 73 is connected to the base of a transistor 76. The emitter of transistor 76 is connected to the positive conductor 62 by a resistance 77, and is connected to the in-verting input of amplifier 73 by a parallel com-bination of resistor 78 and capacitor 80. The inverting input of amplifier 73 is connected to ground by resistance 81, The collector of transistor 76 is connected to ground by a series path comprising . ~
Case 2492 -1~87Z77 resistance 82 and load 83. The amplifier 73 and transistor 76 form a voltage-to-current converter whose gain is controlled by variable resistance 72 and whose zero level is controlled by variable resistance 75.
Table II below shows the figures for the previous Table I extended to show the output.
TEMP R41 VOUT Freq. V-Convert 23 OUTPUT
( C) (ohms) (volts) _hertz) (volts) (ma) 0 9.035 o 0 0 4.0 10.966 2 2000 3.33 9.33 100 12.897 4 4000 6.66 14.66 150 14.828 6 6000 10.0 20.0 The telemetry converter llreceives its power from a regulated DC supply 25 which may, for example, be a BURR BROWN 552 power supply providing + 15 -volts, 0 and -15 volts on conductors 62, 63 and 64 as was previously mentioned. A transformer 84, con-nected to AC supply 12, provides a voltage for bridge rectifier having diodes 85 and a capacitor 86. This is DC supply 26 (Figure 1). The positive output of the bridge rectifier is connected by conductor 87 to a choke 88 to the brush and slip ring 14. The diode 90 is provided to dissipate over voltage if - the connections should be broken when the power ' is on. A diode 91 is connected to the ring 14 for protection against a reversal of connection to the brushes or slip rings 14 and 15. The power from slip ring 14 is again filtered by choke 92, protected as before by diode 93 against over voltage which could result from disconnection with voltage applied.
The choke 93 is connected to a pre-regulator 94 ~ 14 - . ~ - ' :
,., . ~ . . .
lQ~372~ Case 2492 which reduce~ the unregulated DC voltage to 24 volt~
DC ~uitable for DC to DC converter 30. A filter capacitor 95 is connected between choke 92 and pre-regulator 94 to ground.
The DC to DC converter 30 may, for example.
be a BH Industries 2055-24-15 converter which provide~
+ and -15 volts on conductors 53 and 54.
It is believed the operation of Figure 2 will now be clear and no further description i~
required.
The telemetry system provides a reliable transfer of a temperature signal from a rotor of a dynamoelectric machine by direct contact over slip rings and brushes. Changes in resistance between 81ip rings and brushes, or radio frequency inter-ference, will not affect the accuracy of the trans-mission of temperature signals.
Claims (4)
1. A telemetry system for use with a dynamo-electric machine having a rotor and a stator, comprising temperature sensor means mounted on said rotor to sense temperature at a particular location on said rotor, and responsive to temperature at said location to provide a first signal having a voltage which varies with changes in temperature, a voltage-to-frequency converter mounted on said rotor and connected to said temperature sensor means to receive said first signal and to provide a second signal having a frequency which varies with said changes in temperature, a pair of slip rings mounted on said rotor and a brush engaging each slip ring. each brush being mounted to said stator, said voltage-to-frequency converter being connected to said slip rings to provide said second signal on said slip rings, a frequency-to-voltage converter connected to said brushes to receive said second signal and to provide a third signal having a voltage which varies with said changes in temperature, a DC power source connected to said brushes to supply electrical power thereto, and means on said rotor connected to said slip rings to receive said electrical power and to provide a regulated DC power for said temperature sensor means and said voltage-to-frequency converter.
2. A telemetry system as defined in claim 1 and further including a voltage-to-current converter connected to said frequency-to-voltage converter to receive said third signal and to provide as an output a fourth signal having a current which varies with said changes in temperature.
3. A telemetry system as defined in claim 1 in which said temperature sensor means comprises a resistance temperature sensor connected to a constant current source, said resistance temperature sensor being responsive to said changes in temperature to change resistance to vary the voltage thereacross and provide said first signal.
4. A telemetry system as defined in claim 1 in which said means on said rotor connected to said slip rings comprises filter means and regulator means.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA258,174A CA1087277A (en) | 1976-07-30 | 1976-07-30 | Telemetry system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA258,174A CA1087277A (en) | 1976-07-30 | 1976-07-30 | Telemetry system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1087277A true CA1087277A (en) | 1980-10-07 |
Family
ID=4106545
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA258,174A Expired CA1087277A (en) | 1976-07-30 | 1976-07-30 | Telemetry system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1087277A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4545261A (en) * | 1983-03-21 | 1985-10-08 | International Harvester Company | Shaft torque measuring system |
| CN106197728A (en) * | 2016-08-31 | 2016-12-07 | 天津市鸿远电气股份有限公司 | Hygrosensor in distribution box |
| CN110907053A (en) * | 2019-12-16 | 2020-03-24 | 西安闻泰电子科技有限公司 | Temperature detection circuit and electronic device |
-
1976
- 1976-07-30 CA CA258,174A patent/CA1087277A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4545261A (en) * | 1983-03-21 | 1985-10-08 | International Harvester Company | Shaft torque measuring system |
| CN106197728A (en) * | 2016-08-31 | 2016-12-07 | 天津市鸿远电气股份有限公司 | Hygrosensor in distribution box |
| CN110907053A (en) * | 2019-12-16 | 2020-03-24 | 西安闻泰电子科技有限公司 | Temperature detection circuit and electronic device |
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