Theory of Operation
Chapter 3: Theory of Operation
Page 3 - 8
TranStar® PC-100/PC-200/PC-300/PC-350/PC-400/PC-450/
PC-500/PC-550/TR-500/SG-500/OB-450/OB-550/EL-550
Series Stretcher Service Manual (man115re)
LED Outputs
The function power indicating LEDs are illuminated when patient and
caregiver controls are active.
When the controls are active, the regulated DC supply voltage is provided to
the current limiting resistors, R10 and R11, by the patient control switches and
approximately 2.1V DC is dropped across the LEDs to provide the desired
illumination.
Relay Outputs
Under the appropriate input conditions, the relays, K2 - K6, switch the AC
supply voltage to the motors to articulate the stretcher sections.
When the back section of the stretcher is articulating, the relay K1 switches the
AC supply voltage to release the brake on the back section motor. When the
head function up or down button or switch is released, the relay opens, and
back section motion is impeded.
The spark quenchers, SQ1 - SQ4, protect the relay contacts from excessive
damage as a result of arcing when opening and closing.
Potentiometer Calibration Board
The potentiometer calibration board tunes the output voltage of the position
sensor to enable the comparator circuit on the control board to accurately set
the articulation limits of the stretcher independent of the position sensor’s
tolerance.
The calibration procedure for the board is completed at the factory. The output
voltage, which can be monitored on pin 2 of P1 on the control board, should be
approximately 10.8V DC at the head down limit, 5.25V DC at the patient head
up limit, and 3.15V DC at the caregiver head up limit.
If the potentiometer calibration board requires replacement, the entire
potentiometer cable assembly must be replaced.
