Scale System (Optional for the Procedural, Electric, and Trauma Stretchers)
Chapter 3: Theory of Operation
Scale System (Optional for the Procedural, Electric, and Trauma
Stretchers)
The scale has four load beam cells that are attached to the stretcher frame (see
figure 3-4 on page 3-9). These load beam cells detect the weight on the
stretcher and send a signal to the scale assembly which contains the rest of the
scale electronics.
The signals are relayed to the scale P.C. board which acts as the central control
unit for the scale system. This microprocessor based P.C. board does control,
mathematical, memory, and several other functions.
The scale user interface is a membrane switch panel with a color display. It is
part of an integrated service item which also includes the scale assembly cover
and the display driver board.
The scale interface P.C. board connects the scale P.C. board to the
switch/display panel. It also accepts battery input power and contains the
power supply circuitry for the scale system.
Load Beams
The four load beam cells are located near the four corners of the stretcher and
support the complete upper frame. They are resistive bridge sensors excited by
a regulated DC voltage (5 V DC) and output a microvolt signal, thus requiring
a shielded cable. The load beams must always be connected to the scale P.C.
board in a particular order so that the correct calibration constants are used
when a weight is calculated. For this reason the beams are numbered and
connected as such: 1 is left head, 2 is left foot, 3 is right foot, and 4 is right
head.
Scale P.C. Board
The load beam cell inputs are connected to differential inputs on an A/D
converter. The A/D converter digitizes the weight signals and sends them to the
microprocessor. The system has the ability to detect open or shorted sensors. In
order to conserve power, the load beam cells are only powered when a reading
is taken. Calibration constants for each cell are used to accurately calculate a
weight reading. To make sure the correct constants are used, the beams must
be plugged into the P.C. board as such: 1 to P1 (far left), 2 to P2, 3 to P3, and 4
to P4 (far right).
There is a piezo speaker on this board to supply feedback to the user (such as
when a weight reading is initiated, when a weight reading is complete, etc.).
Page 3 - 6
Hill-Rom® Transport, Procedural, and Specialty Stretchers
Service Manual (144386 REV 2)
Summary of Contents for P8000
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Page 441: ...Schematic Wiring Diagram Control Board P N 49603 ...
Page 442: ...Schematic Wiring Diagram Electric Stretcher P N 60389 ...
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