4-1
4.1
Introduction
Applications for the Model 6512 are many and varied and
will depend on your needs. Basically, the Model 6512 can be
used to make many of the same measurements in the range
of ordinary DMMs; however, special characteristics such as
high input resistance and high sensitivity give the instrument
much better capabilities than those of the ordinary DMM.
For example, the typical input resistance for an ordinary
DMM is on the order of 10M
Ω
. In contrast, the Model 6512
has an input resistance of greater than 200T
Ω
(2
×
10
14
Ω
).
The Model 6512 can detect currents as low as 0.1fA
(10
-16
A), while a typical DMM might be limited to current
measurements in the µA range.
In this section, we will discuss some possible applications
for the Model 6512 Electrometer. Keep in mind that these ex-
amples are only representative of what is possible with this
highly sophisticated instrument, and by no means exhaust
the possible uses for the unit.
4.2
Low-level leakage current
measurements
Many devices exhibit low-level leakage currents that may re-
quire measurement. Typically, such leakage currents might
lie in the nA (10
-9
A), pA (10
-12
A) or even the fA (10
-15
A)
range. The Model 6512 is an ideal instrument for such cur-
rent measurements because it can detect currents as low as
0.1fA.
An example of a situation requiring low current measure-
ment is shown in Figure 4-1. In this example, the gate leak-
age current of a JFET is to be measured. Although the device
manufacturer may specify the current value, it is often desir-
able to verify the specification for a particular sample of the
device. Also, the specified leakage current might be at a
higher voltage than required. For example, the specified
leakage current might be 1nA with an applied voltage of
25V, while that figure might be much less at an operating val-
ue of 10V.
This application requires the use of an external voltage source
such as the Model 230 shown in the figure. The voltage source
can be programmed to the desired value or values, and the
leakage current could be measured for each voltage. In this
manner, leakage current characterization studies could be per-
formed with a minimum of effort.
As shown in Figure 4-1, a shielded test fixture should be used
to keep the measurement quiet and stable. A good quality
low-noise triax cable should be used to connect the current
input to the instrument.
Forward and reverse diode currents could be measured in a sim-
ilar manner. The forward leakage current (measured with the
voltage source set to less than 0.6V) can be measured using the
Model 6512 without regard to input voltage burden. High-capac-
itance diodes such as zener devices will present no problem,
since the Model 6512 is unaffected by stray capacitance up to
0.01µF.
4
Applications
Summary of Contents for 6512
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