Loading Errors (dc volts)

Leakage Current Errors

Table 2-1. Thermoelectric Voltages

 

Copper-to-

Approx. μV/°C

 

 

 

 

 

 

 

 

 

 

 

 

 

Copper

<0.3

 

 

 

 

 

 

 

 

Gold

0.5

 

 

 

 

 

 

 

 

Silver

0.5

 

The HP E1312A

 

 

 

 

 

Brass

3

 

 

 

and HP E1412A

 

 

 

 

input terminals are

 

Beryllium Copper

5

 

 

 

copper alloy.

 

 

 

 

 

 

 

 

 

 

Aluminum

5

 

 

 

 

 

 

 

 

Kovar or Alloy 42

40

 

 

 

 

 

 

 

 

Silicon

500

 

 

 

 

 

 

 

 

Copper-Oxide

1000

 

 

 

 

 

 

 

 

Cadmium-Tin Solder

0.2

 

 

 

 

 

 

 

 

Tin-Lead Solder

5

 

 

 

 

 

 

 

 

 

 

 

 

Measurement loading errors occur when the resistance of the device- under-test (DUT) is an appreciable percentage of the multimeter’s own input 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.

26 HP E1312A/E1412A Multimeter Application Information

Chapter 2