Electrical System
Chapter 3: Theory of Operation
3 - 6 Affinity® Four Birthing Bed Service Manual (195826 REV 2)
3. Articulation control - the head motor needs no limit control and uses the actual motor internal
limits for its stroke. The CPLD limit logic controls whether the hilow or foot motor runs or not when
requested depending on the positions of the foot and hilow at the time of the request. The bed
hilow high limit is not really needed and will be disabled external to the CPLD. This logic is needed
in order to keep the foot and hilow mechanisms from running into each other. There are features
integrated into this logic. For instance, if the doctor wanted to lower the foot to the lower level, the
logic may lift the bed up first before lowering the foot section any more. The foot full up limit and
foot full down limit have been disabled external to the CPLD because they are no longer needed.
The logic has been changed so that the head up and bed up functions will not run at the same time.
The bed up function will always take priority over the head up function.
4. Air system control - the CPLD flip-flop outputs control the air system directly, except that the CPLD
provides a caregiver only feature that allows the user to just touch the seat inflate or deflate briefly
and these functions will run continuously for approximately 22 seconds without holding the
controls. Pressing either control will stop the 22 second timer.
5. SideCom® control - the siderail entertainment, lighting controls, and nurse call controls are decoded
as described in
Step 1 on page 3-5, and the output flip-flop signals are sent in a parallel fashion to
the SideCom® board.
Nurse Call Watchdog Timer
The nurse call relay is U27 and isolates the SideCom® circuits from the bed secondary circuits. It can be
operated by any nurse call control in either siderail. It can also get set if there is a fault in the SPI bus.
There is a single unused bit in each siderail 32 bit stream that is set high. Both MISO streams are
“and”-ed in the CPLD and this high bit clears the nurse call watchdog timer, U3. So if one siderail cable is
not connected, the watchdog bit will be low and not reset the timer. The timer will send a nurse call in
approximately 30 seconds.
Main Clock Oscillator
The main SPI clock is set to 24KHz +/- 10%, 50% +/- 5% duty cycle.
Nurse Call LEDs
The bed deviates from the normal SideCom® use of the yellow nurse call and red nurse answer LEDs, it
combines both into one orange LED. When the patient presses the nurse call control and the nurse call
station acknowledges it, the station sets the yellow nurse call signal. The control board, via relay K9,
flashes the siderail orange nurse LED at a 1.0Hz +/- 33%. This shows the patient that the nurse station
has acknowledged the nurse call. When the nurse answers the call, the orange LED will stop flashing
and stay on solid via relay K8.
Air System
The 26.5 V AC air pump is connected to P9-1 and 2. Power to the pump comes directly from the
transformer secondary “24 V AC”. RT20 protects the pump from overcurrent and two relay closures are
required for the pump to operate. Three signals are required to turn on the pump: AC_ON, AIR_SUPER,
and PUMP_AIR. The pump draws about 1.9 Arms. There are three air valve solenoid drivers: lumbar,
exhaust, and seat. The air solenoid valves are connected to logic control P.C. board connector P12. The
solenoid valves are intermittent duty and require PWM to hold them and reduce power to the solenoid.
The power to each solenoid driver has a supervisory relay in series with the 12 V DC rail and each has a
PTC fuse for overcurrent protection. Each driver circuit drives the solenoid at turn on with full power for
1.25 sec +/- 35%, then holds with a 24KHz PWM signal at 50% duty +/- 5%. The holding current is 0.25 A
DC +/- 20%.
To Next Page
Loading...
