Loading Errors (Dc Volts); Leakage Current Errors - HP E1312A User Manual

Loading Errors
(dc volts)
Leakage Current
Errors
26 HP E1312A/E1412A Multimeter Application Information
Table 2-1. Thermoelectric Voltages
Copper-to-...
Copper
Gold
Silver
Brass
Beryllium Copper
Aluminum
Kovar or Alloy 42
Silicon
Copper-Oxide
Cadmium-Tin Solder
Tin-Lead Solder
Measurement loading errors occur when the resistance of the device-
under-test ( ) is an appreciable percentage of the multimeter's own input
DUT
resistance. The diagram below shows this error source.
To reduce the effects of loading errors, and to minimize noise pickup, you
can set the multimeter's input resistance to greater than 10GΩ for the
100mVdc, 1Vdc, and 10Vdc ranges. The input resistance is maintained at
10MΩ for the 100Vdc and 300Vdc ranges.
The multimeter's input capacitance will "charge up" due to input bias
currents when the terminals are open-circuited (if the input resistance is
10GΩ). The multimeter's measuring circuitry exhibits approximately 30pA
of input bias current for ambient temperatures from 0°C to 30°C. Bias
current will double (×2) for every 8°C change in ambient temperature above
30°C. This current generates small voltage offsets dependent upon the
source resistance of the device-under-test. This effect becomes evident for a
source resistance of greater than 100kΩ, or when the multimeter's operating
temperature is significantly greater than 30°C.
Approx. µV/°C
<0.3
0.5
0.5
The HP E1312A
3
and HP E1412A
input terminals are
5
copper alloy.
5
40
500
1000
0.2
5
Chapter 2