Chapter 3
DMM Operation
©
National Instruments Corporation
3-9
DAQMeter DAQCard-4050 User Manual
The DAQCard-4050 is protected against damage from voltages within
±250 VDC or 250 V
rms
in all ranges. However, voltages above these
levels should never be applied to the inputs.
Caution:
To prevent possible safety hazards, the maximum voltage between either of
the inputs and the ground of the computer should never exceed ±250 VDC
or 250 V
rms
.
Input Ranges
The DAQCard-4050 has five basic input ranges for resistance as well as
an extended range. The basic ranges are 200
Ω
, 2.0 k
Ω
, 20 k
Ω
, 200 k
Ω
,
and 2 M
Ω
. With the extended range, measurements up to at least
20 M
Ω
are possible.
The DAQCard-4050 measures resistance by sending a current through
the test resistor and measuring the voltage this current develops across
the resistor. In the Extended Ohms range, the DAQCard-4050 adds a
1 M
Ω
resistor in parallel with the test resistor, and then calculates the
value of the resistor being tested. Table 3-5 shows the accuracy of the
readings in the different ranges.
Table 3-5.
Resistance Input Range Accuracy
Input
Range
Excitation
Current
Percent of
Reading Error
Percent of
Range Error
200
Ω
100
µ
A
0.007%
0.2%
2.0 k
Ω
100
µ
A
0.007%
0.03%
20 k
Ω
100
µ
A
0.007%
0.02%
200 k
Ω
1
µ
A
0.01%
0.03%
2 M
Ω
1
µ
A
0.01%
0.06%
Extended Ohms
1
µ
A
See note below.
Note: The accuracy of measurements made in the Extended Ohms range
varies with the value being measured. For resistances up to 1 M
Ω
, the
accuracy is 0.05%. For resistances between 1 M
Ω
and 20 M
Ω
, the
accuracy is 0.1%. For larger resistances, the error is 0.4%.
!
