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3.1 CIRCUIT DESCRIPTION
The electrical measuring circuit, as shown in Fig. 7.1, consists of a Wheatstone
which the specimen forms one arm and the two calibrated moisture controls form the ratio arms.
The out-of-balance voltage is applied to the inputs of a FET differential amplifier and displayed
on a centre zero meter.
When the function switch is in ZERO position the sample is disconnected and the
'UNITS' arm of the bridge is shorted out. The ZERO control, R 19, is then used to balance the
amplifier for zero output.
Preset resistor, R 16, is adjusted during test to ensure that the instrument reads correctly
when standard resistors are used in place of the electrode.
46882-171 D
Apr. 92
Chapter 3
TECHNICAL DESCRIPTION
bridge in
15
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