Analog output protection requirements

[Sean.C]

Hello,

I am using a PCI-6225 card, and I am trying to understand whether I need to provide additional protection for my analog outputs (or if whatever internal protection it has is sufficient).

The specs include the following information:

Output range ................................... ±10 V
Output coupling ..............................DC
Output impedance ........................... 0.2 Ω
Output current drive........................ ±5 mA
Overdrive protection ....................... ±25 V
Overdrive current ............................ 10 mA

If (hypothetically speaking), the output was set to 10V, and the output was shorted (whether intentionally or on accident), and the short was 1 ohm, which of the following is true?

a) The analog output circuitry overheats and dies.

b) The analog output circuitry goes into some protective fault mode, stops sourcing signal, but recovers as soon as the short is removed.

c) see case b above, but requires the system to be shut down and restarted or some other manual action to reset.

d) The analog output circuit safely limits the current to 5mA (normal output current drive range), providing a signal of 5mV across the short circuit load indefinitely.

e) The analog output circuit safely limits the current to 10mA (overdrive current), providing a signal of 10mV across the short circuit load indefinitely.

f) Something else that I haven't specified.

If instead of a short to ground, the short was to some voltage, how does that change the situation?

I have not been able to find the specifics in any of the documentaion I have been able to find, and I would like to design my system so that I'm not periodically blowing out my daq card.  🙂

Thanks in advance,

Sean

[Justin__D]

Hi Sean,

The link below should help.  Although I'm curious to know why you are worried about this.

Can electrically shorting an anolog output damage my DAQ device?

[Sean.C]

Hello Justin,

I am using the daq card in an automated test system that checks for continuity and measures components on a very dense but primarily passive board.  I am making the various measurements by muxing the analog output and reference to various pins on the connectors (and measuring how the signal appears at other pins).  I was originally planning to have pullups to power on the measurement side so that an OC trace would measure high, a short to ground would measure low, and an ok board would show up in the middle (at a value defined by the final test circuit/topology). 

The concern was whether a short to ground (or a -10V negative rail) when sourcing a positive voltage (or conversely a short to Vcc while sourcing a negative voltage) could damage the daq card.  Even if the card doesn't die, would it go into a fault mode and require manual intervention?  Does the operating range allow 0 ohm shorts to +/-10V?  What about 1kohm? Even if the card is fine, does the card go into a fault shutoff mode, or does it still provide current based on a current limiter (which might allow useful information to be gathered)?

Basically I want to be able to make an informed decision regarding how much time/effort/money to spend protecting the daq card from boards that would fail the tests (via shorts to ground or power) versus how much risk I take that the card might be damaged (and thus need to be replaced).

Thanks,

Sean

[Sean.C]

Also, what if I try to source a voltage to a capacitor that is charged?  If I tried to source -10V to a capacitor charged to 10V from previous measurements (or vice versa), could that cause a problem?  Does this depend on the capacitance value (since a larger capacitance would result in a greater current flow until current limited)?