Keithley 7077, Инструкция по эксплуатации

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Applications
3-3
3.2.2 Voltage divider checks
Thick film resistor networks that are going to be used as volt-
age dividers may be tested using voltages that simulate actu-
al operating conditions. This is a particularly useful test for
resistor networks that have a voltage coefficient specifica-
tion. The test system in Figure 3-1 uses the Keithley Model
230 to source voltage and the Keithley Model 2000 to mea-
sure voltage.
A consideration in these checks is the Model 2000 input im-
pedance on voltage measurements. The input impedance is
diverted across the resistor being measured. The resultant di-
vider resistance is the parallel combination of the resistor un-
der test and the input impedance. As long as the input
impedance is much larger than the resistor being tested, the
error introduced into the measurement will be minimal. Min-
imum input impedance requirements are determined by the
accuracy needed in the measurement. The input impedances
of the Model 2000 are listed in Table 3-1. For better input im-
pedance requirements, the Keithley Model 6517 Electrome-
ter can be incorporated into the test system to measure
voltage.
Another factor considered when checking low voltage divid-
ers is thermal EMFs generated by the matrix card. A matrix
card crosspoint can generate up to +5µV of thermal EMFs.
When making low voltage measurements be sure to account
for this additional error.
Table 3-1
Minimum input impedance — Model 2000 DMM
DC voltage range Minimum input resistance
100mV
1.0V
10V
100V
1000V
>10G
Ω
>10G
Ω
>10G
Ω
10M
Ω
10M
Ω
Even though four-terminal connections are made at the Mod-
el 2000 and the resistor networks, the sense leads are inter-
nally disconnected from the input of the DMM when the
volts function is selected. The simplified test system is
shown in Figure 3-3.
The thick film is tested by applying a voltage across the re-
sistor network and measuring the voltage across each resistor
element and/or across combined elements. In Figure 3-3,
crosspoints C1 and D4 are closed to apply voltage across the
network, and crosspoints A3 and B4 are closed to measure
the voltage drop across R3.
3.3 Transistor testing
A matrix system for testing dc parameters of transistors is
shown in Figure 3-4. This system uses a current source (Kei-
thley Model 224), a voltage source (Keithley Model 230) and
a DMM (Keithley Model 2000) to measure current and/or
voltage. This system tests three transistors, but can be ex-
panded to test more by using additional Model 7077 Matrix
Cards. The Model 707 backplane will accommodate six ma-
trix cards. Daisy-chaining five Model 707s expands the sys-
tem to 30 matrix cards allowing 90 transistors to be tested.
Using a Model 708 Switching Matrix for this application,
three transistors can be tested. Expanding a system based on
the Model 708 Switching Matrix requires an additional Mod-
el 708 Switching Matrix for each additional Model 7077 Ma-
trix Card. This expansion allows up to five Model 708
Switching Matrices to be daisy-chained, which allows 15
transistors to be tested.
NOTE
To check FETs or transistors that have
high gain or low power, equipment that
has lower offset current and higher imped-
ance must be used. To check these devices,
the Keithley Model 7072 Semiconductor
Matrix Card and the Keithley Model 6517
Electrometer can be used.