SR Instruments SR Scales SR2555 Operating Manual

Model SR2555 Stand-On Scale Rev 991222

PART No. MAN2555

S

by SR Instruments, Inc.

SR Instruments, Inc. 600 Young Street, Tonawanda, NY 14150

Tel: [phone] Fax: [phone] URL: www.srscales.com email: [e-mail]

Model SR2555

Stand-On Scale

Operating Manual

Model SR2555 Stand-On Scale Rev 991222

S

by SR Instruments, Inc.

Table of Contents

SECTION I

System Description 1.0
Intended Use 1.1
Specifications 1.2
Theory of Operation 1.3
Assembly 1.4

SECTION II

Button Functions & Basic System Operation 2.0
Special Features – Continuous Weigh/ Auto-Hold 2.1

SECTION III

Calibration 3.0
Periodic Calibration Check 3.1
ESD 3.2
Calibration Procedure 3.3
Calibration Tolerance Table 3.4
Maintenance, Care and Cleaning 3.5
Schematic Diagram 3.6
Parts List 3.7
Component Layout 3.8
Product Labeling 3.9

Model SR2555 Stand-On Scale Rev 991222

SECTION I S S

MODEL SR2555

SYSTEM DESCRIPTION and SPECIFICATIONS

1.0 SYSTEM DESCRIPTION - The SR2555 Scale

System employs the latest in microprocessor
and load cell technology to provide accurate
and repeatable weight data. Four (4)
identically matched transducers are
strategically placed to ensure an accurate
representation of the patient's weight
regardless of weight distribution.
The low power microprocessor circuitry allows
the SR2555 to derive it’s power from six (6)
common “C” cell alkaline batteries which will
provide up to 10,000 weight readings before
needing replacement. This eliminates the
need for an external battery charger or the
danger of an A.C. power supply.
The patient’s weight is displayed on a large 2 x
24 character dot matrix L.C.D. capable of
displaying information in many different
languages. With the push of a button, weight
data may be viewed in both POUNDS and
KILOGRAMS with a displayed resolution of 0.1
LB or 100 grams.

1.1 INTENDED USE The SR2555 is designed for use

as a portable patient weighing system for
ambulatory patients only.

1.2 SPECIFICATIONS

1.2.01 Maximum Weight Capacity - The SR2555 has

a maximum weight capacity of 1000 Lbs. /
450 Kgs. This strength is due in part to the one
piece, solid aluminum cast base.

1.2.02 Platform Size –An generous standing area of

22” x 15” / 55 x 25 cm will accommodate
most all of your patients special needs.

1.2.03 Display Type - The display is a large 2 x 24

Character Dot Matrix L.C.D. with green L.E.D.
back lighting. Highly visible in all light
conditions, you may select one of 7 different
languages to view weight data : ENGLISH

FRANÇAIS ESPAÑOL DEUTSCH ITALIANO
DANSK NEDERLANDS

1.2.04 Display Resolution – The SR2555 will display

weight data in both POUNDS and KILOGRAMS
with a resolution of 0.1 Lb. or 0.1 Kg.

1.2.05 Accuracy - The accuracy of the displayed

weight is 0.1% +/- 1 digit of the displayed
resolution for calibrated range. Refer to the
Calibration Certificate supplied with the scale
for the calibrated range.

1.2.06 Zero - One button Auto-Zero

1.2.07 Memory / Recall - The feature Freezes display

and stores the data in memory. The button is
pressed once again to recall last stored
weight.

1.2.08 Auto Power Down – The system will

automatically power down in 30 seconds to
conserve battery life.

1.2.09 Averaging – An Automatic Digital Filter

samples the weight data to filter motion.

1.2.10 Power Supply - Six LR 14 (“C” cell )Alkaline

Batteries.

1.2.11 Warranty 2 YEAR LIMITED WARRANTY - Each

S scale system is manufactured

with high quality components. SR Instruments,
Inc. warrants that all new equipment will be
free from defects in material or workmanship,
under normal use and service, for a period of
two years from the date of purchase by the
original purchaser. Normal wear and tear,
injury by natural forces, user neglect and
purposeful destruction are not covered by this
warranty. Warranty service must be performed
by the factory or an authorized repair station.
Service provided on equipment returned to the
factory or authorized repair station includes
labor to replace defective parts. Goods
returned must be shipped with transportation
and/or broker charges prepaid. SR Instruments
obligation is limited to replacement of parts
which have been so returned and are
disclosed to SR Instruments satisfaction to be
defective. The provisions of this warranty clause
are in lieu of all other warranties, expressed or
implied, and of all other obligations or liabilities
on SR Instruments part and it neither assumes
or authorizes any other person to assume for SR
Instruments any other liabilities in connection
with the sale of said articles. In no event shall
SR Instruments be liable for any subsequent or
special damages. Any misuse, improper
installation or tampering, shall void this
warranty.

1.2.12 Calibration - Calibration is traceable to NIST

Standards.

1.2.13 Operating Conditions – Care has been taken

in the design of this product to provide
accurate and reliable information under
normal operating conditions. When proper
care is exercised, your scale will provide many
years of reliable service. Normal conditions for
this product would be : Temperature Range:

20oC to 30oC (68o to 85of) Humidity Range:
0%-95%. Avoid exposure to high pressure

water or steam.

1.2.14 Transport and Storage – To maintain proper

operation of this instrumentation transport and
storage conditions should not vary outside the
following conditions: Humidity: 0% to 99%,

Ambient Temp:-200C to +500C

1.2.15 Patient Applied Part Classification – TYPE B

1.2.16 Accessories – The SR2555 is available with

optional handrails for 3-Sided support (part no.
FG3070) and a Height Gauge (part no. 3086)
107 – 203 cm / 42” – 80”.

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Model SR2555 Stand-On Scale Rev 991222

Figure 2. Force Cell bending with applied weight (displacement exaggerated for clarity)

SECTION I S S

SR2555 Theory of Operation

1.3 The SR2555 patient weighing system is a digital weigh scale. Four strain-gauge force cells convert the force of a patient’s

weight into an analog signal. This signal is amplified by a chopper-stabilized operational amplifier and converted to a digital signal
by a quad slope 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 dot-matrix liquid crystal display.

The base of the SR2555 patient weighing system contains four strain gauge based
force cells (Analog board J1..4). Each cell contains four strain gauges mounted in a full
Whetstone-bridge configuration (Figure 1.) These bridges convert the physical bending of the
force cell (Figure 2.), due to the patient’s 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 chopper-stabilized operational amplifier (Analog
board U1). The amplifier is configured to current sum the output of each cell, with
potentiometers (Analog board R1, R2, R4, R5) serving to adjust the sensitivity (voltage out per
unit of weight applied) of each bridge. The offset potentiometer (Analog board R3) produces
a small current, which nulls the output of the amplifier for a n unloaded system.

The output of the operational amplifier is digitized by the quad
slope analog to digital converter (Analog board U5). The
converter integrates the analog signal onto the integrating
capacitor (Analog board C9) over a short interval. The
integrating capacitor is then discharged at a rate proportional
to the reference voltage applied to the converter
(Analog board C11 and C10). The residual voltage
on the integrating capacitor (Analog board C9) is
then multiplied by a factor of eight and again
discharged at a rate proportional to the reference
voltage (Figure 3.). The residual voltage from this
discharge is again multiplied by eight and again
discharged. The time taken to discharge the
capacitor is proportional to the voltage from the
operational amplifier, which is proportional to the
weight on the force cells. The time is stored as a
binary number in the analog to digital converter
and is transferred to the micro-controller when the
conversion is complete.

The micro-controller (Readout U1)
averages and filters the digital output of the
analog to digital converter, subtracts the value
saved during the system tare operation and scales
the filtered output to the appropriate units (Kg or
Lb.) then displays the result on the dot-matrix liquid crystal display. The micro-controller performs a rolling average of two seconds
of data for continuous weigh and, for AutoHold, the micro-controller averages two seconds of data, minimum, before locking in
on the reading. If the data variance is greater than 0.1% in the AutoHold mode, the micro-controller will reset the filter and start a
new averaging period.

The micro-controller can be placed in a calibration mode (Readout J5), where the system can be re-calibrated. In the
calibration mode, the result of the weigh operation is scaled to match the value entered by the decimal keypad. This new
calibration factor is then stored in the non-volatile memory (Analog board U4).

Figure 3. Analog to digital converter timing diagram (from Maxim MAX132 data sheet).

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