Users manual
ET3260 and ET3260A
6 1/2 Digit Multimeter
40
Error (%) =
In order to reduce load error influence and the pickup noise to the minimum extent, it is needed
to set the multimeter input resistance >10GΩ during the measurement of 100mV, 1V and 10V
measurement range. For 100V and 1000V measurement ranges, input resistance is fixed as
10MΩ.
5.1.3 DCI load error
During DC current measurement, since multimeter is not ideal and it has certain amount of input
resistance, electric measurement during the situation where multimeter and test circuit are
connected in series will cause error. As shown in the following figure, equate the multimeter to
an ideal voltmeter, and connect with resistance R in paralleled way.
Vs=Voltage source
Rs=Circuit resistance
R=Multimeter bypass resistance
When circuit internal resistance approximates with multimeter internal resistance, it will
seriously influence measurement accuracy, then you should select multimeter’s next higher
measurement range to reduce the error to an acceptable level. The following table lists
multimeter internal resistances under different measurement ranges
Measurement Range
Internal Resistance
Measurement Range
Internal Resistance
10uA
11kΩ
100mA
1Ω
100uA
1kΩ
1A
0.01Ω
1mA
100Ω
12A
0.01Ω
10mA
10Ω
5.1.4 Noise control
Voltage controlling power-line noise
One of the advantages of integral (A/D) converter is that it can control relevant power-line noise
existing in DC input signals, which is called norm noise control or NMR. Multimeter realizes
norm noise control through conducting integral to DC input in a fixed time period. If the integral
time is set as integer multiple of power-line period (PLC), these errors (and their harmonics)
approximate to zero after being averaged.
Multimeter provides four integral options (1, 2, 10 and 100 PLC) to realize norm noise control.
Multimeter firstly measures power frequency (50Hz or 60Hz), and then determines
corresponding integral time.
Common-mode control
In ideal situation, multimeter is totally separated from circuit benchmarked against ground.
