22
7.
SPAN CALIBRATION (Sensitivity Adjustment)
The electronic balance measures mass by electronically compensating for
terrestrial gravitation. Since gravitation acceleration varies slightly in
different areas of the world, span calibration is required when the balance is
installed. Temperature also affects accuracy. Calibration should be
performed whenever there is a significant temperature change. It is good
practice to calibrate the balance before making important measurements and
whenever the balance is moved or disturbed, such as if something falls on
the pan.
Though the temperature coefficient of sensitivity of the balance is adjusted
at less than ±2ppm/°C, readability 0.1mg corresponds to 1ppm (0.1mg/100g
= 1×10
-6
) in regards to 100g weighing. This means that a slight temperature
change may cause a measuring error. The CAW series balances are designed
to automatically perform span calibration when there is a change in room
temperature. This feature is called
"Automatic Span Calibration (PSC)"
and is only available on the CAW series balances. The stability of
sensitivity is maintained within ±2ppm regardless of any change in
environmental temperature. It is possible for the operator to perform span
calibration at any time. This is referred to as
"Manual Calibration."
Manual Calibration can be performed using an external weight
(CAW/CAX/CAY series) or the built- in weight (CAW/CAX series only).
Span calibration can be automatically performed at designated times up to
three times in a day. This is referred to as
"Clock-CAL"
and is only
available on the CAW series balances.
7.1 Span Calibration Using the Built -in Weight
Only the CAW/CAX series balances have the built- in weights. The
following procedure describes span calibration using the built- in weights.
Procedure
(1) Warm-up the balance.
F
See Section
3. “WARM-UP.”
(2) Verify that the balance is level.
(3) Verify that the balance pan is empty and press the
→
O/T
←
key to
zero the display.
(4) From the mass display, press the CAL/MENU key several times.
When
"Func.SEL"
appears, press the
→
O/T
←
key.
