An American-Standard Company SERVICE MANUAL 6082 OVERSPEED SYSTEM AND MAGNETIC AXLE GENERATOR January, 19 79 A-79-100-2287-1 * * * * OPERATION AND MAINTENANCE INSTRUCTIONS UNION SWITCH & SIGNAL DIVISION WESTINGHOUSE AIR BRAKE COMPANY Swissvale, PA 15218
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An American-Standard Company
SERVICE MANUAL 6082
OVERSPEED SYSTEM AND
MAGNETIC AXLE GENERATOR
January, 19 79 A-79-100-2287-1
* * * * OPERATION AND
MAINTENANCE INSTRUCTIONS
UNION SWITCH & SIGNAL DIVISION WESTINGHOUSE AIR BRAKE COMPANY
Swissvale, PA 15218
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Section
CONTENTS
I INTRODUCTION
1.1 GENERAL INFORMATION 1.2 AXLE GENERATOR 1.3 SHAPER-LIMITER PRINTED CIRCUIT BOARD 1.4 SPEED GOVERNOR PRINTED CIRCUIT BOARD
3.1 AXLE GENERATOR MAINTENA.J.~CE AND TEST 3. 2 SHAPER-LI.MITER/V=O PCB TEST 3.3 SPEED GOVERNOR PCB TEST
IV PARTS LIST
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
4. 1 SHAPER LIMITER PCB 4.2 SPEED GOVERNOR.PCB
L!ST OF ILLUSTRATIONS
System Application Circuits
Shaper~Limiter Block Diagram (Speed Signal/V=O)
Speed Governor Block Diagram
Axle Generator Assembly
Shaper Limiter Waveforms
Standard Circuit Diagrams of Printed Circuit Boards
Speed Governor Waveforms
Standard Circuit Diagram of Plug-!n Circuit
Shaper Limiter/V=O PCB
Figure 10. Speed Governor PCB
ii
Page
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1/2 1/2
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5
5 8
8
8 13 17
21
21 25
3/4
7
9/10
11/12
14
15/16
18
19/20
23
27
..
SECTION I
INTRODUCTION
1.1 GEHERAL INFORMATION
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The SS-3 Overspeed Protection subsystem is designed to provide visual and audible warning to the locomotive operator when an overspeed condition occurs, and to automatically apply braking if the operator fails to correct the overspeed condition within a specified period of time. Overspeed detection is accomplished by electronically measuring the actual speed of the locomotive by means of an axle generator and then comparing the measured speed to the allowable speed information received from the rail signals. When an overspeed condition exists, visual and audible alarms are activated and unless the operator initiates corrective action within a specified period of time, braking circuits are automatically activated to bring the locomotive to a stop.
The SS-3 Overspeed Protection subsystem consists of an axle generator and printed circuit boards mounted in a common card file. The description and function of each of these items are as follows:
(Refer to Figure 1)
1.2 AXLE GENERATOR
The axle generator is a electro-mechanical device which is directly coupled to the axle of the locomotive, and consists of a magnetic impulse generator enclosed in a rugged cast iron housing. The electrical connections from the generator are routed through a connector of special design mounted to the housing and through the attached rubber tubing which provides maximum protection against moisture and abrasion.
The steel gear of the magnetic impulse generator is coupled to the locomotive axle, and rotates in the magnetic field of a stationary coil wound on a permanent magnet. An alternating current potential is produced in the coil when the gear rotates and the frequency generated is proportional to the speed of the locomotive.
6082, p. 1/2
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Figllre 1. System Application Circuits
6082, p. 3/4
1.3 SHAPER-LIMITER PRINTED CIRCUIT BOARDS
This board receives a speed signal from the axle generator to produce three outputs:
a) An output pulse with its frequency proportional to locomotive speed.
b) A vital output signal to indicate when the locomotive is not moving.
c) A simulated tachometer signal.
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Tnis board also produces an audio frequency signal and -20 VDC.
1.4 SPEED GOVERNOR PRINTED CIRCUIT BOARD
The Speed Governor accepts logic inputs from the Relay Matrix corresponding to the allowable locomotive speeds and the input pulses from the Shaper-Limiter which are frequency proportional to the locomotive speed. The Speed Governor then compares these two inputs (allowable and measured speeds) and if the measured speed exceeds the allowable speed, the energizing signal to the overspeed relay is removed causing the relay to indicate that an overspeed condition exists by activating the visual and audible alarms. The operator must respond within a specified period of time or automatic braking action will result.
The Speed Governor characteristics are modified by the wheel wear switch, which compensates for speed signal errors due to wheel wear. Speed 'input for Speed Governor requirements is produced by, and received from the shaper-limiter printed circuit board.
SECTION II
DESCRIPTION OF OPERATION
2.1 SHAPER-LIMITER (N451404-6801) (See Figures 2 and 6)
The Shaper-Limiter (Speed Signal/V = 0) board has three principal functions. It provides a vital output if the locomotive is not moving, it shapes the tachometer signal produced by the axle generator into a narrow pulse and it provides a series of pulses in order to simulate the axle generator input while the locomotive is stopped. In this manner the overspeed circuitry, particularly the speed governor is kept active while the locomotive is stopped and
6082, p. 5
prevents a brake application. Circuit design assures that these pulses will not appear while the locomotive is moving in excess of approximately 5 MPH. The Speed Signal/V = 0 board also includes a 115 KHz amplifier and a rectifier to provide the negative DC power requirements for the Speed Governor board.
The magnetic pick-up in the axle generator is shunted by a tuning capacitor and connected to the input of a high gain amplifier. The output of this amplifier is coupled back to its input through a dual input gate. When the gate is enabled the positive feed back produced will cause the amplifier to oscillate at a frequency determined by the resonant circuit of the magnetic pick-up and its shunting capacitor.
When the gate allows the amplifier to oscillate, the output is rectified by a detector, passed through a time constant and then to a switch that effects control by means of a change in its output potential level. This output is connected to the dual input gate which is disabled when the potential level from the switch changes to a lower value as a result of the amplifier going into oscillation. There is no feed back when the gate is disabled and the amplifier will stop oscillating resulting in no output to the detector, time constant or switch. The loss of input causes the switch to change and present a high potential level to the gate which then allows feed back and the amplifier will oscillate.
Thus the gate and loop will switch on and off at a low repetitive rate determined by the time constant and a high frequency will intermittently appear across the pick-up. The on and off switching pulses are passed to a 50/50 duty cycle circuit and then to an output pin that provides an AC signal present only when the locomotive velocity is approximately zero. The on and off switching pulses are also amplified and rectified by a second amplifier and are used to blank the speedometer which would otherwise register the V = 0 pulses as locomotive speed when the locomotive is not moving. Additional pulses are generated in the pick-up coil when the gear in the axle generator starts to rotate and these pulses are passed to the first amplifier and the detector. When the frequency of these pulses exceed the time constant that controls the switch, a steady potential is presented to the switch which in turn closes the gate causing the high frequency oscillations to cease, and the pulses pass through the second amplifier to the speedometer driver circuit.
A decrease in locomotive speed reduces gear rotation in the axle generator and thus the frequency of the generated pulses also decrease. When the pulse rate becomes inadequate to hold the electronic switch in the "gate off" state, the high frequency oscillations will appear and the loop and gate will switch on and off at the low repetitive rate. In order to obtain a good transition from the V = 0 condition, a small amount of hysteresis is introduced to cause a snap action in the transition zone.
6082, p. 6
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MAGNETIC PICK UP
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DETECTOR
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TIME CONSTANT
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INHIBIT LINE
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FROM . SPEED
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Figure 2.
(-) DC MAKER
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·20VDCTO SPEED GOV.
Shaper-Limiter Block Diagram (Speed Signal/V=O)
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2.2 SPEED GOVERNOR (N451404-7601 & 7602) (Refer to Figures 3 and 8) --.,.
The function of the Speed Governor printed circuit board is to monitor and limit the speed of the train by providing a visual and audible warning to the operator followed by automatic brake application in the event that the operator fails to acknowledge a reduced speed cab signal or make a brake application when an overspeed condition exists.
The speed governor receives two inputs from the shaper-limiter/ V = 0 board. One is a squarewave speed signal and the other is a negative DC voltage (-20 VDC) which is routed through the relay logic before it reaches the speed governor.
The speed signal enters an amplifier (1) that has its gain set to produce an output of a given level, then the signal is routed through a low pass filter network causing the amplitude to become inversely proportional to its frequency. The filter output connects to a second amplifier (2) which drives the primary of the speed selection transformer (Tl). One of the several taps on the primary is selected depending on the cab signal speed selection. The tap selected determines the primary to secondary voltage ratio and it receives the -20 DC volts from the shaper-limiter board. A step-up tap is used for high speed selection. The output of Tl is amplified (by amp 3) and rectified to produce a negative DC voltage that is applied to the level detector.
When the DC voltage reaches a specific value it makes the oscillator in the level detector operate and this signal is amplified by an amplifier (4) that drives two relays. One relay is the warning relay that drops immediately when an overspeed condition exists. The other is the overspeed relay and it has a delayed drop away, usually 2 seconds.
The frequency of the speed signal is proportional to the speed of the train, however the amplitude is set by the vital low voltage power supply that has its output determined by the wheel wear adjustment. The speedometer is also dependent on the vital power supply.
SECTION III
MAINTENANCE
3.1 MAGNETIC AXLE GENERATOR MAINTENANCE AND TEST (Refer to Figure 4)
If problems are encountered with the Magnetic Axle Generator, a defective magnetic pick-up should be suspected. To check the pick-up, disconnect the Axle Generator cable and test for the following:
b) A DC resistance to ground (axle generator housing of .5 megohms or more from either cable lead.
c) A coil inductance of from 60 to 85 millihenrys.
WARNING
IF THE MAGNETIC PICK-UP IS REPLACED OR REMOVED FOR ANY REASON AIR GAP BETWEEN THE PICK-UP FACE AND THE TOOTHED t'VHEEL MUST BE SHIMMED FROM .003" to .004". WHEN REINSTALLING THE MAGNETIC PICK-UP, BE SURE TO APPLY LOCKTITE GRADE "A" (UA041608) TO THE THREADS OF THE ATTACH-
MENT SCREWS (SEE ITEM 20, FIGURE 6). CLEAN ANY DIRT, GREASE, OR FOREIGN MATERIAL FROM THE SCREW THREADS BEFORE APPLYING LOCKTITE.
After removing or replacing the magnetic pick-up, it is imperative that the air gap between the pick-up and toothed wheel be set at .003" to .004" (see Figure 4). In order to check the gap (using a feeler gauge) it is nec~ssary to remove the generator face plate and to turn the locomotive wheel until a toothed wheel of the Axle Generator is aligned with the center of the pick-up.
3.2 SHAPER-LIMITER/V=O PCB TEST
The waveforms in Figure 5 are provided as an aid in performing periodic testing and also for locating trouble when the circuit board is suspected of being defective. A card extender board (part number N398028) should be used to allow access to test points on the P. c. Boards.
The magnetic pick-up must be connected when making the waveform measurements otherwise no waveforms will appear.
Connect the ground lead of the oscilloscope to the ground side of the circuit board and place the probe on the circuit board at the test points designated on the circuit diagram in Figure 6. The displayed waveform should compare to that shown in Figure 5 for the particular point being tested. If the displayed waveform does not agree, then the circuit components in that particular stage should be checked for failure or a change in value.
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Figure 6. Standard Circuit Diagrams of Printed Circuit Boards
6082, p. 15/16
3. 3 SPEED GOVERNOR PCB TEST
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The waveforms in Figure 7 are provided as an aid in performing periodic testing and also for locating trouble when the circuit board is suspected of being defective.
Connect the oscilloscope in the same manner as described in paragraph 3.2 and use the test points shown in the circuit diagram of Figure 8. Compare waveforms as explained in Paragraph 3.2.
Resistor, 2K Ohms, 5%' \W Resistor, 56K Ohms, 5%, \W Resistor, 330K Ohms, 5!!c o I \W Resistor, lSK Ohms, S!!c o I \W Resistor, 220 Ohms, S!!c o I \W Resistor, 1. 2K Ohms, S!!c o I \W Resistor, 6.2K Ohms, S!!c o I \W Resistor, 20K Ohms, 5!!c o I \W