What is the maximum continuous voltage you can apply to PXI-5922 input?

[Magne]

Our circuit produces a saturation voltage of about 14 V when not in use. Is it okay to let this connect to the ch0 and ch1 inputs of the PXI-5922 Digitizer, or will it destroy the unit? The specifications says maximum input overload 7Vrms with |peaks|<10V at 50ohm and |peaks|<42V at 1Mohm. It is not clear to me which of these conditions apply.

When saturating at 14V, our signal is measured over a near infinite resistance. 

[Jennifer O]

Hi Magne,

The default impedance of the NI-5922 is 1MOhm.   It is designed with overload protection on that setting to 42V.  14V for a short period of time will not damage the board, but you should be very careful not to accidentally put the board into 50 Ohm mode. 

The overload protection is designed mainly for cases where the digitizer is exposed for a short period of time to an out of range voltage.  This for example allows the user to experimentally find the best vertical range to use for a particular signal.  In your case, you will knowingly be saturating the input, perhaps for an extended period of time.  I do not have data to advise you on what the long-term effects are of continuously saturating the input.   

If you are concerned with the long-term health of your digitizer, you may wish to consider external clamping of your signal to keep it within the digitizer's input range or disconnecting your circuit when not in use for long periods of time.  If you can also use the largest range (10V as opposed to 2V) I would recommend it.

- Jennifer O.

[Magne]

Thank you, that was clarifying. I guess we will have to fit the voltages externally beforing applying them to the digitizer.