Maximum voltage to analog input in NI625x card

[Rafi2003]

HI,

The specifications states that the maximum input voltage is 11V (pos&neg)

1. Is there any protection for higher inputs?  What voltage will cause demage to the card?

2. I use a differential inputs with a range of plus/minus 1V.  Due to some circumstanses in my hardware, there is a situation that one input will be at 5 V while the other is floating.  Is there any danger in this situation?

3.  I noticed that if I read the above input I get a saturated level (14.8V) and it stays like that until I read a "normal" value.  Is there any danger in this condition?

Thank

RK

[Deborah_B]

Hello Rafi2003,

You should definitely not exceed that +/- 11V specification, as even that is pushing it since that 11V maximum working voltage technically refers to the signal voltage plus the common-mode voltage.  Here's the explanation page behind that spec. Exceeding this will add most likely bring high inaccuracy or unseen data before actually blowing it out, but neither is advised. You should be able to measure the floating input situation with differential configuration just fine, but 'care should be taken to ensure that the common-mode voltage level of the signal with respect to the measurement system ground remains in the common-mode input range of the measurement device' (Field wiring and noise considerations for analog signals, especially note the 'Measuring Floating (Nonreferenced) sources section). Adding the bias resistor should take care of the railing you see.

Regards,

Deborah Y.

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[Rafi2003]

Hi,

Is this also correct for a short pulse?

The system I'm testing generates 500 usec pulse at 14hz.  The normal pulse is 8.3V but it is possible to reach around 20 volts under a certain conditions.  Does such a short pulse may demage the card?

Thanks

RK

[Seth_B.]

Hello RK,

For NI 625x DAQ devices, there is overvoltage protection of ±25V on up to 4 pins (this is because the protection weakens when guarding against higher power, more channels means less protection).  Thus, as long as the pulse is of a finite duration, your card shouldn't be damaged.  What you will see is a "railed" reading, returning the maximum value that the input can read (~11V).

Regards,

[Rafi2003]

Hello Seth,

what does it mean overvoltage protection on up to 4 pins?  Any specific pins?  which pins?  Please elaborate on it.

Thanks

RK

[Seth_B.]

This spec (which can be found on page 2 of the Specifications) is for any 4 Analog Input pins.  This spec is defined in terms of number of pins because the overvoltage protection weakens as more AI pins are put into an overvoltage condition.