Loading Errors (Dc Volts); Leakage Current Errors - HP 34401A User Manual

Chapter 7 Measurement Tutorial

Loading Errors (dc volts)

Loading Errors (dc volts)
Measurement loading errors occur when the resistance of the device-
under-test (
input resistance. The diagram below shows this error source.
V
s
To reduce the effects of loading errors, and to minimize noise pickup,
you can set the multimeter's input resistance to greater than 10 G for
the 100 mVdc, 1 Vdc, and 10 Vdc ranges. The input resistance is
maintained at 10 M for the 100 Vdc and 1000 Vdc ranges.

Leakage Current Errors

The multimeter's input capacitance will "charge up" due to input bias
currents when the terminals are open-circuited (if the input resistance
is 10 G ). The multimeter's measuring circuitry exhibits approximately
30 pA of input bias current for ambient temperatures from 0
Bias current will double ( 2) for every 8
above 30
the source resistance of the device-under-test. This effect becomes
evident for a source resistance of greater than 100 k , or when the
multimeter's operating temperature is significantly greater than 30
R
s
HI
V
s
LO
) is an appreciable percentage of the multimeter's own
DUT
R
s
HI
R
i
LO
C. This current generates small voltage offsets dependent upon
°
i
R
C
b i
V = ideal DUT voltage
s
R = DUT source resistance
s
R = multimeter input resistance
i
Ideal
( 10 M
Meter
Error %
C change in ambient temperature
°
i = multimeter bias current
b
R = DUT source resistance
s
C = multimeter input capacitance
i
For DCV ranges:
Ideal
0.1V, 1V, 10V: C
i
Meter
100V, 1000V: C
For all ACV ranges: < 50 pF
Error (v) i
b
or >10 G )
100 x R
s
R R
s i
C to 30 C.
° °
C.
°
< 700 pF
i
7
< 50 pF
i
x R
s
199