Amprobe BDM40-UA Bench-Digital-Multimeter - Manual (Page 15)

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converter. This offset will not significantly affect any readings until you try to measure signals almost at the lower
limit of the meter. For example:
Given: An offset of 40 digits Given: An offset of 20 digits
0.40mV in 200 mV range 0.20mV in 200 mV range
Input signal = 10mV in 200 mV range Input signal = 10mV in 200 mV range
2
0.4
2
10 rms Total + =
2
0.2
2
10 rms Total + =
0.16 100 + = 0.04 100 + =
100.16 = 100.04 =
= 10.01 mV = 10.00 mV
The error will be about 0.01mV the error is not significant
CURRENT MEASUREMENTS
All of the controls and terminals used to make current measurements are located on the front panel. The AC mA
and DC mA function switches determine the measurement function. The colored area around the 20A switch
extends up and to the right to enclose the six range values for the 20A measurement function. Push the range
switch immediately above the value to be measured.
As the colored areas around the terminals indicate, the red test lead should be plugged into the 2A or 20A terminal
and the black test lead should be plugged into the COMMON terminal.
WX WARNING
INSTRUMENT DAMAGE AND OPERATOR INJURY MAY RESULT IF THE FUSE BLOWS
WHILE CURRENT IS BEING MEASURED IN A CIRCUIT WHICH EXHIBITS AN OPEN
CIRCUIT VOLTAGE GREATER THAN 600 VOLTS.
Burden voltage error
When a meter is placed in series with a circuit to measure current, you may have to consider an error caused by
the voltage drop across the meter (in this case, across the protective fuses and current shunts). This voltage drop
is called burden voltage. The maximum full scale burden voltages for your instrument are: 0.3V for the four lowest
ranges, and 0.9V for the 2000mA, 20A ranges. These voltage drops can affect the accuracy of a current
measurement if the current source is unregulated and the resistance of the shunt and fuse represents a significant
part ( 1/ 1000 or more) of the source resistance. If burden voltage does present a problem, the percentage error
can be calculated using the formula below. This error can be minimized by selecting the highest current range that
provides the necessary resolution.