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AD16 OMNIBUS Module: Offset and Gain Calibration

Questions on all Omnibus modules using any II host board.

Moderators: srodriguez, gmiller, ollie

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daniel.hartman

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  • Location: Santa Fe, NM

AD16 OMNIBUS Module: Offset and Gain Calibration

PostWed Aug 09, 2006 3:01 pm

Greetings all,

Does the AD16 come with each of its AD7722s calibrated, or is that something the user must do?

Unfortunately, I am not at my hardware, and I cannot test this myself. If it is calibrated, then it seems to me that you would want the CoefficientSource property to default to csRom rather than csDefault. Is there a reason one would want to run the AD16 at csDefault?

Many thanks for your help.

Dan
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gmiller

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  • Location: Simi Valley, CA.

AD16 OMNIBUS Module: Offset and Gain Calibration

PostWed Aug 09, 2006 4:04 pm

The A/D on this Omnibus card can self calibrate if set in the right mode. This calibration is for the internal A/D only. This will not take out external circuitry errors. If the calibration is done the error will be reduced. There is no internal coefficients to be used and this must be done each time the power is turned on. If the program is set to enable this it does take a small amount of time to go through the procedure before data can be taken.

Gary
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jhenderson

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Re: AD16 OMNIBUS Module: Offset and Gain Calibration

PostWed Aug 09, 2006 5:30 pm

daniel.hartman wrote:Greetings all,

Does the AD16 come with each of its AD7722s calibrated, or is that something the user must do?

Unfortunately, I am not at my hardware, and I cannot test this myself. If it is calibrated, then it seems to me that you would want the CoefficientSource property to default to csRom rather than csDefault. Is there a reason one would want to run the AD16 at csDefault?

Many thanks for your help.

Dan


Dan -

We cal all channels of the module at the factory using a custom jig and instrumentation traceable to NIST. We derive the gain and offset coefficients for each channel which optimally correct for the actual in-system gain and offset errors present on each channel.

When we do the cal, we use csDefault, so that unity gain and zero offset are in effect during the derivation of the actual in-system errors. Later, when you select csRom coefficients, you're using the factory-learned values, which should give corrected results for each channel. Each sample which passes through the logic gets corrected using y=mx+b where m is the channel-specific gain and b is the channel-specific offset value learned at the factory.
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