Appendix 8 Concerning Noise Countermeasures
A18
Insulation from noise sources (temperature measurement by thermocou-
ple)
The analog input channels are insulated from the chassis and each other. Therefore,
the instrument allows you to attach the thermocouple directly to a conductor with a
potential to measure it, provided that the voltage to ground does not exceed the
maximum rating. If noise is likely affect measurement, wrap heat-resistant tape
around the thermocouple for insulation, or use an ungrounded thermocouple and
electrically insulate the input line.
Setting the Digital Filter
To remove noise from input signals, the digital filter can be set for the analog chan-
nels.
The longer the recording interval is, the larger
the n
oise reduction effect becomes;
this ensures highly accurate measurement with little scatter.
See: For reco
rding interval and cutoff frequency (p.141)
For example, assuming that the digital filter is set
to 60Hz, noise reduction in the
supply frequency is maximized at a recording interval from 2 sec. to 1 hr.
Inserting a Capacitor in the Signal Line
When noise affects the signal source directly or when measuring high-frequency
pulses, it is effective to insert a capacitor between the "+" and "-" input terminals so
that the noise does not enter the LR8431-20. When inserting a capacitor, use one
with a rated voltage that is equal to or exceeds the input voltage.
When a capacitor is inserted between the "+" and "-" input terminals, there are no
re
strictions o
n the recording interval because the filter is applied before the channel
scan operation.
The capacitance of the capacitor should range from several F to
several thousand
F. Insert the capacitor between the "+" and "-" in-
put terminals.
Thermocouple
Device being
Tested
Instrument
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