over voltage protection on USB-6215

[masam7799]

I'm a teacher using the USB-6215 multifunction DAQ to develop new content for the students. I'm trying to understand fully the consequences of overvoltage on this device because a student could easily connect a wire at the wrong place :

-As I understand from the product specifications, I can apply up to ±20V between a digital input or output and DGND without damaging the device

-If the device is on, I can apply up to ±30V between an analog input or output and AIGND/AOGND

-If none of the ground pins are connected (it can happen if a student forget it), the device is OK for up to 60V between any pin and earth ground

Is my understanding correct ?

Thank you,

M.Samson

[Finnabon]

Hi M. Samson,

From what I saw from the specifications, digital input is protected up to 20V from DGnd.
The analog input is only safe when on at +/-30V and when off at +/-20V.

I believe the 60 V specification I believe you are referring to has nothing to do with overvoltage protection but more to do with measurement abilities. For example, earth ground is 0V. Your specified device ground may be 40V. You can then measure voltages from 30-50V. So this specification is just stating how far away from earth ground the actual signal can be to function properly.

Additionally,

Do not connect a DO or PFI output lines to any external signal source, ground signal, or power supply.
Understand the current requirements of the load connected to DO or PFI output signals. Do not exceed the specified current output limits of the DAQ device. 
Do not drive a DI or PFI input line with voltages outside of its normal operating range. The PFI or DI lines have a smaller operating range than the AI signals.

Kind regards,

Allie

[masam7799]

Thanks Allie, that really clears up the 60V specification.

I understand that I should not connect a DO or PFI output line to any signal source, ground or power supply. I'm protecting those outputs with a schottky diode so that a wiring error with a 24 volt source will not cause an overvoltage condition on the DO (what I get is a voltage drop from 5V to 4.8V, but that's OK for my applications).

I have one more question considering the analog outputs.

From the "NI USB-621x Specifications" documents, I see "Overdrive protection.......±30V"

I'm assuming that it means that the device will be protected from a wiring error with a 24V power supply. Is that correct ?

thank you again,

M.Samson

[Finnabon]

I believe that is correct.

Allie