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

[etechstan]

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%.

[david.bolt · Accepted solution]

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 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