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10. Calibration
10. Calibration
10.1 What is calibration?
10.1.1 The Necessity of Calibration
Calibration is required to accurately weigh items with an electric balance. Calibration must be per-
formed in these conditions:
• When the location of the installation site is changed (even when moved within the same room).
• When the room temperature changes.
• Also, daily calibration before use is recommended.
The AUW-D/AUW/AUX series are set to operate fully-automatic span calibration PSC by default. The
AUY series requires span calibration using external weights.
The Essential Role of Span Calibration for the Use of Electronic Balances
The measurement desired when using an electronic balance is the measurement of mass. However, an elec-
tronic balance cannot detect mass directly. Instead, it detects the weight (the weight is the Earth’s attraction on
the item, gravity) and displays the mass as computed from the weight. The proportion of mass to weight
depends on the gravitational acceleration at the location. By placing calibration weights of accurately known
mass on the electronic balance, the corresponding weight for that mass can be recorded. This allows the mass
of any item that is subsequently weighed to be computed from its weight and accurately displayed. The record-
ing and setting of weight-mass relation is known as span calibration.
The necessity can be recognized this way for example, the gravitational acceleration in the Japanese cities of
Kyoto and Tokyo are 979.70775 cm/s
2
and 979.76319 cm/s
2
respectively, with a difference of about 0.0057%.
This means that if a balance is calibrated in Kyoto and the balance is moved to Tokyo, an object of 100.0000g
mass will exhibit 100.0057g on the balance, generating an error of two digits.
Always perform span calibration at the installation site before using the balance to correct for this effect.
In addition, electronic balances use a permanent magnet and a coil in their weight detecting system. Even with
compensation, a permanent magnet generates a sensitivity difference of up to
±
2ppm (two millionths) with every
1°C fluctuation in temperature. When measuring for example, a 100g object, this difference amounts to
±
2mg,
which means a possible error on the final two digits displayed on the electronic balance. If the temperature
changes by 5°C after calibration, an object of 100.0000g may appear to increase to a maximum of 100.0010g.
When there is a change in temperature, always calibrate again for accurate measurement.
Note
Using a verified balance as a legal measuring instrument in the EU:
The balance must be used within the temperature range indicated on the
verification label.
When PSC (refer to
), fully-automatic span calibration, is not acti-
vated, operator must carry out span calibration (refer to
) upon blinking
of the Weight Symbol.
