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Page 62 of 97
Issue: 1.04
7.1.3 Voltage Measurements
The automatic input reversal of used by the microK when measuring voltage
provides good zero stability. However, small differences between the thermal
EMFs generated by the devices used to make these reversals on each channel
mean that the zero offset needs to be checked for each channel. Once the zeros
offsets have been checked/adjusted, it is only necessary to check the span on one
channel since this part of the measurement system is common to all the channels.
7.1.3.1
Zero Voltage Offsets
Short out the 4 measurement terminals on all 3 channels using a piece of un-
insulated copper wire (use pure copper wire to avoid generating unwanted
thermal EMFs) for each channel:
V
I
Configure the microK to measure a Default Thermocouple on the 0.125V range
with units of Volts. Use 1 sample per reading and 100 readings in the rolling
statistics (see section 3.6). Select the
Multi
tab
and clear the statistics for all 3
channels. After the microK has collected at least 100 readings (shown as
Mean of
last…
in the
Multi
tab, check that the
Mean
for each channels is less than
0.000000250 (0.25µV) and that the standard deviation (
S.D.
) is less than
0.000000050 (0.05µV).
7.1.3.2
Voltage Span Check
Connect a stable, low noise voltage source with a nominal value of 50mV to
channel 1 of the microK using low thermal EMF wire and connectors (copper or
