# Multifunction DAQ

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## Where do I find data on the gain accuracy and gain stability of a NI6225?

I need to answer the following two requirements;

Gain Accuracy: The gain accuracy shall be at least ±1% of the selected dynamic range.

Gain Stability: Thirty minutes after applying power to the system, the gain stability shall be better than 0.33% per minute. The total change in 1 hour shall not exceed ±3%.

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Accepted by topic author etechstan

## Re: Where do I find data on the gain accuracy and gain stability of a NI6225?

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.

#### AI Absolute Accuracy Table

Nominal Range Residual
Gain
Error
(ppm of
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

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
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