Section 4
OM6530-C1-00
19 November, 2019
4-11
The integration time is affected by the selection of the capacitor, threshold and test
voltage according to the formula:
2 x C x R x V
threshold
T =
_________________________
V
source
Where: T is the integration time in seconds,
R is the unknown resistance in ohms,
C is the integrator capacitance in farads,
V
threshold
is the threshold voltage in volts,
V
source
is the test voltage in volts.
The operator may use the timing diagram of Table 8-5 to select the measurement
constants without calculation. For example, if the unknown resistor value is
approximately 100 MΩ, the operator will find the sloping 100 MΩ line on the test
voltage graph (top of the page). The intersection of the 100 MΩ line with the horizontal
10 V test voltage line gives an input current of 100 nA (vertical line). Following the 100
nA line to the 2700 pF threshold voltage graph (center of page) it can be seen that
selecting a 10 V threshold will give an integration time of 540 ms which is within the
optimum range of 0.54 to 54.0 seconds. The selection of the 0.1 V threshold should be
avoided because it would give an integration time of 5.4 ms.
Another thing that should be considered is the voltage used within the measurement. If
the measurement is being performed at low voltages (100 V or less) then the integration
time is best to be within 5.4 to 54 seconds. This longer integration time will improve the
stability of the inherently lower signal to noise ratio with lower voltages.
