QuadTech 1865, Инструкция по эксплуатации, Страница: 41 / 87

Operation Page 41 of 87
Table 2-1: Range Current
Range Maximum Current
1 1mA
2 100uA
3 10uA
4 1uA
5 100nA
6 10nA
7 1nA
Example:
When measuring an unknown of 200M
Ω
at 100V, Ohms Law tells us that the device
under test would draw 0.5uA ( I = 100V/200M
Ω
). Based on the above one would expect
the 1865 instrument to auto range from the 1mA to 1uA range (50% of maximum
current) or the user to select the 1uA range if prior knowledge of the expected results is
known.
NOTE
When measuring in the current mode, in order to calculate the unknown resistance, the
input resistance of the instrument (5k
Ω
) must be taken into consideration. For further
discussion of this refer to Display Type in ¶ 2.6.3.1
The measurement range capability is represented graphically in Figure 2-14. By locating
the charge voltage on the vertical axis and the measured resistance, or expected measured
resistance, on the horizontal axis one can determine the optimum range. When Auto
range is selected the range switching is done automatically and the specified instrument
accuracy always applies. If a range is selected other than auto and the resistance value
for the given voltage does not fall in the range band shown measurement accuracy as
specified does not necessarily apply.