1794-IF4I stray voltage

[Jasondelane]

Hi all. I have a 0.5-4.5 analog joystick wired into a 1794-IF4I and all is well except for one thing.

I was expected that if the 5 volt power supply or any of the wiring between the power supply and joystick were to fail, that I would get zero volts to the IF4I and could use this to indicate a failure.

The problem that I have is that when I simulate a failure by disconnecting the positive DC lead on the power supply, I'm actually getting around 1V indicated on the IF4I, which is higher than the 0.5 minimum of the stick, thus making it impossible to indicate a failure.

Is there something I could possibly be doing wrong? When everything is connected I'm indicating the full range of voltage with no spikes or strays, but the open wire generates a voltage. The only solution I can see at this point is to buy sticks with microswitches that indicate the direction of stick travel and correlate this to the voltage indicated on the IF4I.

Any help is greatly appreciated!

 

[drbitboy]

We don't know your circuit (yet; you can fix that ), but:

• Finding and eliminating the source of stray voltage seems like a possible solution.
• How is your grounding?
• Could a high-Ω resistor be placed somewhere clever to pull that 1V down closer to 0V if the DC lead is pulled, without affecting normal operation?

Also, pulling the DC lead is different than losing the power supply; what happens if the power supply loses one of its input leads?

 

[Jasondelane]

High-ohm resistor

We don't know your circuit (yet; you can fix that ), but:

• Finding and eliminating the source of stray voltage seems like a possible solution.
• How is your grounding?
• Could a high-Ω resistor be placed somewhere clever to pull that 1V down closer to 0V if the DC lead is pulled, without affecting normal operation?

Also, pulling the DC lead is different than losing the power supply; what happens if the power supply loses one of its input leads?

How many ohms of resistance do you think it would take to pull the voltage down without affecting the 0.5-4.5 volts process voltage?