differential voltage levels

[POB]

Hi!

I have a NI-USB 6212, The analog inputs are speced to -10 to 10 volts. Is it possible to measure a signal which varies between 27 and 27,5 Volts directly. By connecting

27V to CH-

27,5 V to CH+

thus, have a span of 0,5 Volts?

Or do I have do use a voltage divider to get the signal within the spec region and an instrument amplicfication curcuit for better accurcy?

Can the first soulution damage the device? 

regards

[JB]

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I have a NI-USB 6212, The analog inputs are speced to -10 to 10 volts. Is it possible to measure a signal which varies between 27 and 27,5 Volts directly. By connecting

27V to CH-

27,5 V to CH+

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No, you must use a voltage divider. This voltage can't be measured and the card may be damaged. Extracts from page 1 of the specifications :

• Maximum working voltage for analog inputs

(signal + common mode) ................ ±10.4 V of AI GND

• Overvoltage protection (AI <0..31>, AI SENSE)

Device on ....................................±30 V for up to two AI pins
Device off ...................................±20 V for up to two AI pins

[POB]

Thanks for your answer. I guessed that was the case.

Somehow I just figured since the the ch- was 27V and the ch+ was 27,5 the actual potential was 0,5V, well within the spec, which was going to safe some curcuits. Oh well I have to solve it the, well not so, hard way.