Will a voltage divider be adequate to read a 28V pulse into NI-6251 Digital Input ports?

[usv]

Hi all, 

I'm a life science scientist trying to read a 28V 4.2mA pulse signal sent from my animal operant box into my NI-6251.

Seems like a voltage divider should do the work. But should I be aware of anything else such that my NI card don't get burned? And should I be concerned of the current coming into the NI card?

Thanks for your help! 

[Mark_SAI · Accepted solution]

Hello,

Looking at page 7 and 8 of the NI-6251 datasheet it shows that the maximum voltage is 5.25V, so use a voltage divider to bring 28V down to 5V and you should have no problems, providing that you can guarantee your 28V source will always be at 28V or below and that your resistors are fairly accurate. Under no circumstances should you provide more than 5.25V to the digital input. 

The only concern you could have about current is that the resistor divider isn't affected by the impedance of the digital input which is unlikely (datasheet says 250uA max), so if you use resistors around the 5k to 50k range, you should be fine. Also be sure of your resistor divider wiring as if its the wrong way round, you'll have a big chance of breaking the card! 

Hope this helps!

[TheOceanPlanet]

So did this work for you? I'm trying the same thing with a 12V pulse output flowmeter into an NI6009 DAQ.