Hill-Rom P870, Manual

Page: 103 / 231

Electrical Theory of Operation
Chapter 3: Theory of Operation
Page 3 - 6 Resident
TM
LTC Bed Service Manual (man136rc)
3
Electrical Theory of Operation
The Hill-Rom
®
Resident
TM
LTC bed incorporates three separate motor actuators
to provide the following operational features:
• Hilow (bed height)–this function raises and lowers the entire sleep surface.
• Head section–this function raises and lowers the head section of the bed.
• Knee section–this function raises and lowers the knee section of the bed.
• Automatic contour–this is an automatic function that is activated during
operation of the head section (unless locked out). As the head section
inclines, the knee section of the bed also inclines to a maximum of 15
o
(± 2
o
). If the automatic contour is temporarily disabled by pressing both the
HEAD Up and KNEE Down buttons at the same time, releasing the KNEE
Down button will allow the automatic contour function to activate
regardless of the degree of head section inclination.
These features are controlled by using the handset and/or the optional siderail
control panels in conjunction with the control lockout box.
When the Resident
TM
LTC bed is plugged into a 120V AC, 60 Hz power source,
a transformer within the control box reduces the incoming voltage to 42V AC.
This 42V AC is then rectified to 42V DC and supplied to the input side of a
“normally open” switching circuit and to the input side of a “normally open”
motor actuator circuit.
The switching circuit consists of the following:
• The coils of six different relays, one for each possible motor actuator
function
• Four isolation switches in the caregiver control lockout box
• Six momentary contact switches in the handset control
• Six momentary contact switches in each siderail control
• Two limit switches in the automatic contour module