maximum peak voltage input to a PXI-5114

[plibby@efw.com]

What is the maximum DC input to the PXI-5114?

[Matt_E.]

For normal operation you would not want to exceed the peak voltage of the range you have selected on your digitizer (For example if you are using the 10Vpp range you should not exceed +/-5V DC because the input to the ADC will max out and the input circuitry will clamp at some point to prevent damage).  The device is protected beyond the peak voltage of the selected range but this protection is dependant on how you have configured your input.  More information on the maximum input voltages can be found in the spec sheet by going to Start -> programs -> National Instruments -> NI-Scope -> Documentation -> Specifications and selecting the 5114. 

Protection for the 50 ohm and 1 Mohm ranges is somewhat different because in 1 Mohm the primary concern is breakdown voltages of parts in the input signal path.  In the 50 ohm modes the board must also make sure that too much power is not dissipated in the 50 ohm termination resistor.  If the board detects a power overload in the 50 ohm resistor it will trigger an overload error and switch back to 1Mohm mode to further protect itself.  At this point 1Mohm limits will apply but it would not be a good idea to use the board in a system where you are expecting the 50 ohm terminator to be frequently overloaded.

Hope this helps.

-Matt

[plibby@efw.com]

Matt,

So it looks to me according to the specification that the maximum voltage allowed is 20 VDC if set for the 40vp-p setting.

Is this correct?

Peter

[Matt_E.]

That is the largest voltage voltage you can put in and still be able to measure correctly, anything greater will staturate the ADC and give you an incorrect reading.  The device will not be damaged as long as your peak input voltage is less than 35V DC.

-Matt

[Matt_E.]

As a side note if you are trying to measure voltages larger than +20V and don't need the full +/- 20V range you can use the vertical offset feature of the digitizer to shift the input range up.  The 40Vpp range has a max offset of +/- 15V so if you set it to +15 you could read a maximum voltage of + 35V and a minimum voltage of -5V.  If you don't need the negative part of the range for your application this may be a helpfull feature.

-Matt

[plibby@efw.com]

Thanks Matt,

I plan on measuring 7 and 25 volt peak digital signals.

Peter