Seaward RH9A Series - Manual (Page 9)

6
RH9A Series High Resistance Decade Boxes Operating Instructions
When using the instrument set the required dial setting
on the RH9A before applying the voltage from the device
being tested.
Before altering the resistance setting of the RH9A always
switch off the applied voltage from the device being
tested to avoid the possibility of actually switching 5kV
d.c. which could be harmful to the RH9A.
When using the higher values on the RH9A i.e. above a
setting of 1GΩ the following comments should be noted.
1. Connection leads should be kept as short as possible
2. Having set the dials on the RH9A and the test object
switched on, the operator should stand away from the
instrument and avoid moving as this could infl uence
the measurement and give an unstable reading.
3. It should be noted that an operator moving near the
test and wearing synthetic clothing will cause unstable
readings.
4. Using high resistance settings on the RH9A and having
a low test voltage on the device being tested requires a
lot of patience as the test currents involved are very
low and it may take some time to resolve a fi nal reading.
5. Measurement of high resistance values is dependent
upon:
a) Relative humidity
b) Ambient temperature
c) Measuring time
d) Polarity of test voltage
e) Previous test voltages applied
6. If the value to be selected is equivalent to the fi rst
position of the dial, always use position 10 on the
previous dial, this will have a better uncertainty of
measurement. This is of course, subject to the max volts
for the dial used not being exceeded.