NI 9203 built-in protection

[j.maunder]

Hi all. I understand from reading the data sheet that the NI 9203 +/-20mA 8 channel analogue input module has over-voltage protection up to 30VDC channel to COM, for one channel at a time.

My question is:

a) what would happen if I connect a 1A 24VDC supply directly to one of the input channels with the COM channel grounded.

b) as for (a) but with reversed polarity.

For context, I am designing equipment that will be connected to the DAQ device in the field and so there is the potential for accidental shorting of wires. I am trying to establish whether I need to provide overcurrent protection external to the module.

Thank you for your help.

[j.maunder]

I'm surprised an answer hasn't been forthcoming for this question. Perhaps I need to supply more detail?

[j.maunder]

Can I get some help with this question please?

[Logan_K]

I assume the power supply you are connecting is a 24VDC supply with up to 1A current limit (as opposed to a 1A current source)? For the first case, the input impedance of the 9203 is 138 ohms, so it will limit the current to 174mA, and since the voltage is under 30V, it should be fine as long as this is only on one channel. If you connect the 24V supply to multiple channels, the device would be at risk of dissipating too much heat across the internal resistors.

For the reverse case, you will effectively be shorting the power supply to ground, so if the power supply limits its output to 1A, then you will probably end up with 1A of current directly through the ground connection - which is fine as long as you have a large enough gage wire to prevent overheating. If the power supply blows a fuse at 1A, you will end up with a power supply that requires a new fuse. Either of these scenarios are fine for the 9203, but probably not so good for the power supply.