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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 performed in these conditions:
x When the location of the installation site is changed
(even when moved within the same room).
x When the room temperature changes.
x Also, daily calibration before use is recommended.
The CAUW-D/CAUW/CAUX series are set to operate fully-automatic span calibration PSC
by default. The CAUY 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 electronic 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 recording 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/s2 and 979.76319 cm/s2 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.
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