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4.70
CALIBRATION
Your scale has been carefully calibrated at
the factory.
This calibration involves matching and
tuning of the load cells and readout electronics.
The
scale calibration should be checked annually.
Only
use
calibrated,
certified scale test weights
for this
purpose.
Traction or physical therapy weights are
NOT acceptable since their actual weight can often
be in error as much as +/-10%.
Calibration weights
may be purchased from SCALE-TRONIX® or a local
scale dealer.
An alternative to calibration weights is
the weight comparison
method.
This requires
a
known accurate, calibrated scale.
A fixed weight is
"weighed"
on the calibrated scale; then the same
weight is placed on the scale for comparison.
PRECISION TEST CALIBRATION WEIGHTS ARE
AVAILABLE FROM SCALE-TRONIX®.
THREE (3) 25 KILOGRAM TEST WEIGHTS ARE
RECOMMENDED.
ORDER PART NO. 20021.
(25 KG Test Weights)
Large
changes
in
calibration
offen
indicate
a
damaged load cell or faulty readout component.
It is
generally
recommended
that
if
calibration
is
necessary for your scale it should be returned to the
factory.
Calibration
procedure
follows
for those
situations where this is not desirable.
Calibration
should not be attempted
by those not having the
proper tools or knowledge of electronic systems and
their attendant shock hazards.
CALIBRATION MODE:
Some versions of the printed circuit board contain a
blue "dip switch" consisting of 4 switches in one
package focated in one corner of the main printed
circuit board.
These switches control the calibration
mode described in section 4.71 below.
If your board
contains
these
switches
use
that
calibration
procedure.
Later versions use a front panel access
Procedure for entering the calibration mode consisting
of specific sequence of button pushing during power
up. This procedure is described in section 4.72.
471
CALIBRATION PROCEDURE (WITH DIP
SWITCHES)
Switch the readout into "calibration mode" by
first noting and recording the position of the individual
rockers (1 through 4) of DIP switch SW1.
Then set
each rocker of DIP switch SW1
to the "off" position.
Remove any items from the platform.
Turn the power
on by pressing the "ON™ pushbutton on the front panel.
(On
battery
powered
readouts
a jumper
lead
or
programming shunt can be connected between pins 1
and 2 of J2 on the 23005 instrument board to prevent
the readout from fiming out and shutting off during the
calibration process.)
The readout will power-up and eventually display a
number,
which represents the zero offset value of the
platform and load cell transducers, in tenths of pounds
{0.1 pound).
Note and record this value.
(Even
though
your scale may
be "kilograms
only"
in
operation, pounds are used internally because of their
finer resolution.)
Units conversion is as follows:
10.0 Kilograms = 22.0
(22.046)
pounds.
25.0 Kilograms =
55.1
(55.116)
pounds.
50.0 Kilograms = 110.2
(110.231)
pounds.
75.0 Kilograms = 165.3
(165.346)
pounds.
Add the specified test weight to the platform. Note the
new number displayed.
Subtract the original zero
offset value from this new number to obtain the scale's
displayed value of the calibration weight.
(Example: The zero offset value is "117" (representing
11.7 pounds).
Adding the specified three 25 kilogram
test weights
(equivalent to
165.3
pounds)
to the
platform produces a reading of "1771". The difference
is 1771-117
= 1654 (equivalent to 165.4 pounds).
This would indicate the calibration is 0.1 pound "high".
Using the specified three 25 kilogram test weights a
difference of 165.3 +/- 0.1 pound should be obtained.
If necessary adjust potentiometer P1 (span adj.) on
the
instrument
board
until the
correct
value
is
obtained.
Remove the test weights and recheck the
zero offset value.
Note that adjusting P1 may also
alter the zero offset value.
Repeat the process as
necessary to obtain the correct difference.
Once the calibration is satisfactory reset DIP switch
SW
to its original position and allow the scale to time
5002, 5102, 5602, 6002, 6102, 6202, 6502, 6702
28
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