Model SRV714 Series
Operating and Service Manual
Part No. MAN714_200601
Page 7 of 14
S
Instruments, Inc.
,
600 Young Street, Tonawanda, NY 14150
Tel: 716-693-5977 Fax: 716-693-5854 URL:
email:
Copyright 2020
S
Instruments, Inc.
MAINTENANCE and CLEANING
The SRV714 is constructed from durable
stainless and aluminum tube with a high
density anti-slip plastic surface. Exercise
caution when cleaning the high density
plastic surface as it can be scratched by
abrasive cleaners. Waterproof seals can
also be damaged. We recommend mild
soap and water for general cleaning and
disinfecting.
STORAGE and TRANSPORTATION
If storing this equipment for periods longer than three (3) months, remove the batteries. To
maintain proper operation of this instrumentation, storage and transport conditions should not vary
outside the following conditions: Relative Humidity 0% to 85%, Ambient Temperature 14
F to
122
F (-10
C to +50
C).
THEORY OF OPERATION
SR Instruments patient weighing systems are digital scales. Strain-gauge force cells convert the force
of an applied weight into an analog signal. This signal is amplified by an operational amplifier and
converted to a digital signal by an analog to digital converter. The digital signal is transferred to a
micro-controller where it is filtered, converted to appropriate units and displayed on a liquid crystal
display.
Strain-gauge force cells each contain four strain gauges mounted in a full Whetstone-bridge
configuration. These bridges convert the physical movement of the force cell, due to the applied mass
on the system, into minute changes in electrical resistance. These changes in resistance produce a
voltage difference across the Whetstone-bridge, which is amplified by the operational amplifier. The
amplifier is configured to current sum the output of each cell, with potentiometers serving to adjust the
sensitivity (voltage out per unit of weight applied) of each bridge.
The output of the operational amplifier is digitized by the analog to digital converter.
The micro-controller averages and filters the digital output of the analog to digital converter, subtracts
the value saved during the system zero operation and scales the filtered output, then displays the result
on the liquid crystal display. The micro-controller performs a rolling average of data for continuous
weigh.
DO NOT use pressurized water or steam. The
scale system contains microprocessor circuitry
and strain gauge sensors that may be adversely
affected by exposure to such an environment.
WARNING