Hi etechstan
Heres the link for the technical specification sheet for the NI 6225:
http://sine.ni.com/ds/app/doc/p/id/ds-15/lang/en
The gain accuracy depends on your selected range and using the formula from the table below you can calculate the Absolute Accuracy and Gain and Offset Error.
Nominal Range |
Residual
Gain
Error
(ppm of
Reading) |
Gain
Tempco
(ppm/°C) |
Reference
Tempco |
Residual
Offset
Error
(ppm of
Range) |
Offset
Tempco
(ppm of
Range/°C) |
INL Error
(ppm of
Range) |
Random
Noise,
σ (µVrms) |
Absolute
Accuracy
at
Full
Scale1 (µV) |
Sensitivity2
(µV) |
Positive
Full
Scale
|
Negative
Full
Scale
|
10 |
-10 |
75 |
25 |
5 |
20 |
57 |
76 |
244 |
3,100 |
97.6 |
5 |
-5 |
85 |
25 |
5 |
20 |
60 |
76 |
122 |
1,620 |
48.8 |
1 |
-1 |
95 |
25 |
5 |
25 |
79 |
76 |
30 |
360 |
12.0 |
0.2 |
-0.2 |
135 |
25 |
5 |
80 |
175 |
76 |
13 |
112 |
5.2 |
AbsoluteAccuracy = Reading · (GainError) + Range · (OffsetError) + NoiseUncertainty
GainError = ResidualAIGainError + GainTempco ·
(TempChangeFromLastInternalCal) + ReferenceTempco ·
(TempChangeFromLastExternalCal)
OffsetError = ResidualAIOffsetError + OffsetTempco · (TempChangeFromLastInternalCal) + INL_Error
1 Absolute accuracy at full scale on the analog input channels is determined using the following assumptions:
TempChangeFromLastExternalCal = 10 °C
TempChangeFromLastInternalCal = 1 °C
number_of_readings = 100
CoverageFactor = 3 σ
For example, on the 10 V range, the absolute accuracy at full scale is as follows:
GainError = 75 ppm + 25 ppm · 1 + 5 ppm · 10 GainError = 150 ppm
OffsetError = 20 ppm + 57 ppm · 1 + 76 ppm OffsetError = 153 ppm
AbsoluteAccuracy = 10 V · (GainError) + 10 V · (OffsetError) + NoiseUncertainty AbsoluteAccuracy = 3,100 μV
2 Sensitivity is the smallest voltage change that can be detected. It is a function of noise.
Accuracies listed are valid for up to one year from the device external calibration. |
If you have any furthur questions please do not hesitate to contact me.
Kind regards
David
Applications Engineer
National Instruments UK
Many thanks for using the NI forums and I look forward to your reply.
Kind regards
David
Applications Engineer
National Instruments UK