OPTA Analog Input voltage offset

Official Hardware Opta
1

Hi, I'm using the OPTA (wifi) main unit and EMR expansions to read analog voltage from a sensor outputing 1-5V. The reading is not accurate, I'm currently getting an offset of about 0.2V. For this specific issue I know it's not a problem to correct this offset but I'm worried that as I connect more sensors this offset would change. Can someone please explain why this happens and if it's possible that in the event I will be connecting more sensors to additional analog inputs, the offsets/scaling would change?

Thanks

2

Well it would take a long time to explain it, but this is not uncommon that an internal A/D converter has an offset. It is basically what you get when you try and get an analogue device to operate in a closely coupled digital environment.

It should stay constant and will not change when you read more sensors. Providing of course that the sensors have an impedance range in the 10K to 50K region.

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3

Thanks for your response. My sensor's analog output have the following spec:

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Can this 1K impedance present a problem?

4

Yes

So you will need to compensate for both offset and gain errors. However, it has such poor accuracy and repeatability it may not matter too much

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5

Thanks - I'm fine with preforming a calibration curve that I can rely on at +-2% repeatability. Can inputs be affected by each other in this scenario?

6

I'm not an Opta expert and I can't say with 100% certainty that there is no interaction between ADC channels, although I would be surprised if there was.

Maybe an expert will see your post and respond.

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