8060A
Instruction Manual
4-10
Table 4-1. Voltage Input Divider
Function Range
Input
Divider
Range of A/D Converter Input
DC Voltage
200 mV
2V*
20V
200V
1000V*
1/1
1/1
1/100
1/1000
1/1000
-200 mV to +200 mV
-2V to + 2V
-200 mV to + 200 mV
-200 mV to + 200 mV
-2V to + 2V (1V max. input)
AC Voltage
200 mV
2V
20V
200V
1000V*
1/1
1/10
1/100
1/1000
1/1000
0 to -200 mV
0 to -200 mV
0 to -200 mV
0 to -200 mV
0 to -2V (-0.75V max. input)
*Integrator gain in a/d converter reduced by factor of 10.
4-7. Current Measurement
Current measurements are made using a double-fuse-protected, switchable,
five-terminal current shunt (0.1 ohm, 1 ohm, 10 ohm, 100 ohm, or 1 kilohm)
to perform the current-to-voltage conversion required by the a/d converter. A
block diagram of current measurements is shown in Figure 4-5. When the dc
current function is selected, the dc voltage drop across the shunt is filtered
and applied to the input of the a/d converter. When the ac current function is
selected the ac voltage drop across the shunt is ac-coupled to the input of the
true rms ac converter. The dc representation of the ac voltage is filtered and
applied to the input of the a/d converter. All current ranges use the ±200 mV
a/d converter input range.
4-8. Resistance Measurement
Resistance measurements are made using a ratio technique as shown in
Figure 4-6. When the resistance function is selected, a series circuit is
formed by the ohms source, a reference resistor for the voltage divider
(selected by the range switches), and the external unknown resistor. The ratio
of the two resistors is equal to the ratio of the voltage drop across each of
them. Since the voltage drop across the reference resistor and the value of
the reference resistor are known, the value of the second resistor can be
determined. Input protection during resistance measurements consists of a
thermistor and a double-transistor clamp.
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