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Slide Valve Actuator Troubleshooting Guide
Slide Valve Actuator Theory of Operation
The slide valve actuator is a gear-motor with a
position sensor. The motor is powered in the for-
ward and reverse directions from the main com-
puter in the control panel. The position sensor
tells the main computer the position of the slide
valve. The main computer uses the position and
process information to decide where to move the
slide valve next.
The position sensors works by optically counting
motor turns. On the shaft of the motor is a small
aluminum “photochopper”. It has a 180 degree
fence that passes through the slots of two slotted
optocouplers. The optocouplers have an infra-
red light emitting diode (LED) on one side of the
slot and a phototransistor on the other. The
phototransistor behaves as a light controlled
switch. When the photochopper fence is block-
ing the slot, light from the LED is prevented from
reaching the phototransistor and the switch is
open. When photochopper fence is not blocking
the slot, the switch is closed.
As the motor turns, the photochopper fence al-
ternately blocks and opens the optocoupler slots,
generating a sequence that the position sensor
microcontroller can use to determine motor posi-
tion by counting. Because the motor is connected
to the slide valve by gears, knowing the motor
position means knowing the slide valve position.
During calibration, the position sensor records the
high and low count of motor turns. The operator
tells the position sensor when the actuator is at
the high or low position with the push button.
Refer to the calibration instructions for the de-
tailed calibration procedure.
The position sensor can get “lost” if the motor is
moved while the position sensor is not powered.
To prevent this, the motor can only be moved elec-
trically while the position sensor is powered.
When the position sensor loses power, power is
cut to the motor. A capacitor stores enough en-
ergy to keep the position sensor circuitry alive
long enough for the motor to come to a complete
stop and then save the motor position to non-vola-
tile EEPROM memory. When power is restored,
the saved motor position is read from EEPROM
memory and the actuators resumes normal function
This scheme is not foolproof. If the motor is moved
manually while the power is off or the motor brake
has failed, allowing the motor to free wheel for too
long after the position sensor looses power, the ac-
tuator will become lost.
A brake failure can sometimes be detected by the po-
sition sensor. If the motor never stops turning after
a power loss, the position sensor detects this, knows
it will be lost, and goes immediately into calibrate
mode when power is restored.
Summary of Contents for VSM 71-701
Page 1: ...1 VPN 35391S February 2006 Rev 05 Price 60 00...
Page 2: ...2...
Page 20: ...20...
Page 52: ...53 Pre Start Up Check List...
Page 99: ...99 Recommended Spare Parts List...
Page 104: ...104 Gate Rotor...
Page 110: ...110 Main Rotor VSS...
Page 112: ...112 Main Rotor VSR...
Page 114: ...114 Slide Valve Cross Shafts and End Plate...
Page 118: ...118 Capacity Slide Volume Slide Carriage Assembly Slide Valve Carriage Assembly...
Page 134: ...134 Miscellaneous Frame Components VSS Screw Compressor VSR Mini Screw Compressor...
Page 138: ...138 C FlangeAdapter Components 630 620 610 640 601 641 630 601 620 610 640 641 642 650 651...
Page 140: ...140 Replacement Parts Tools...
Page 144: ...144 GaterotorAssembly...
Page 148: ...148 Main Rotor Slide Valve Cross Shafts and End Plate Models 71 401 Only Counter clockwise...
Page 152: ...152 Main Rotor Slide Valve Cross Shafts and End Plate Model 501 701 Only Clockwise...
Page 154: ...154 Volume Ratio Capacity Slide Carriage Assembly Slide Valve Carriage Assembly...
Page 158: ...158 Miscellaneous Frame Components Model VSM 501 701 Model VSM 71 401...
Page 160: ...160 Replacement Parts Accessories Housing Accessories C Flange Assembly...
Page 166: ...166 Haight Pumps...
Page 170: ...3 Refrigerating Specialties Division...
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Page 244: ...168...