Hill-Rom VersaCare P3200, Service Manual

Page: 128 / 379

Electrical System
Chapter 3: Theory of Operation
Deployment Control
There are three inputs to the deployment control circuitry: DC power from the
bed, the steer switch, and the enable switch. Also, the deployment motor must
provide limit switch output to reflect the extended (deployed or down) and
retracted (stowed or up) positions of the deployment motor.
If bed power is absent, the steer switch has been closed, neither handle enable
switch is closed and the drive mechanism is not down, the logic turns on the
deployment motor to lower the mechanism. The logic subsequently turns the
motor off when the extended limit switch opens or a twelve second timer times
out, or if bed power is applied or the steer switch opens.
Similarly, if the bed power is applied or the steer switch is open and the drive
mechanism is not up, the logic turns on the motor to raise the mechanism. The
logic subsequently turns the motor off when the retracted limit switch opens or
the timer times out, or if bed power is removed or the steer switch closes.
Whenever the mechanism is not down or bed power is present or the steer
switch is open, the logic asserts an /INHIBIT signal to the motor controller to
prevent it from driving the drive motor. Conversely, if the mechanism is down,
bed power is absent and the steer switch is closed, the /INHIBIT signal is
removed allowing the motor controller to drive the drive motor.
Enable Switch Logic and Relay
The enable switch, when closed while the drive mechanism is fully down,
provides an input to the logic which removes the /INHIBIT input to the motor
controller. At the same time, a relay is energized which connects the drive
motor to the motor controller output allowing the controller to drive the drive
motor. When the enable switch is subsequently opened, the logic again asserts
the /INHIBIT signal to the motor controller, causing it to decelerate the drive
motor to a stop. The relay opens after a six second delay, allowing the motor
controller time to stop the motor before disconnecting the motor from the
controller. As a back-up, the normally closed relay contact shorts the motor
producing a further braking effect. This effect will slow or stop the drive motor
even if the battery becomes disconnected.
Drive Motor Over-temperature Protection
The PACM includes a connection for a normally closed thermal switch. The
opening of such a switch produces an input to the logic that causes the
/INHIBIT signal to the motor controller to be asserted. The motor controller
will bring the drive motor to a stop in this case. In situations where the drive
motor is operated under high load (such as powering the bed up a ramp) for
Page 3 - 14 VersaCare™ Bed Service Manual (MAN333 REV 2)