BX-2AD2DA-2B joystick application q

[MikeR]

I have a Hall Efffect joystick connected to BX-2AD2DA-2B configured for 0-5v (joystick centers at 2.5v). When i disconnect the joystick the input value in PLC indicates 2.5v. That works great for this system because movement will stop if the joystick is disconnected.
What if 0v was stop and 2.5 was half speed. is there a way to know program a safety check for this?

I've had to deal with similar situations with +/-10v proportional valves connected to EIO modules that lose connection and the output goes -10v. what a mess that made.

Thanks

[Garyhlucas]

I can't understand how the disconnected joystick could cause the PC to see 2.5 volts. I would expect zero.  Do you have a resistor in this circuit applying a bias? If your power source is not 5 volts but a higher voltage dropped through a resistor then something like this would make sense to me.  If you are concerned about know whether the joystick is connected I'd consider using resistors on both ends of the post  so value put out by the stick is never 0 or 5.  Kind of like a 4-20ma sensor loop where a value below 4ma indicates a problem.

[MikeR]

I expected zero as well. the power source is 5v from a converter. when the joystick is disconnected the plc input register shows what should be 2.5v (same for both inputs i'm using). so, if the input is floating (not connected to anything) i should expect the lowest possible value?

maybe some bias from a different power supply used for the output section of this combo module?

I'll do more testing in the shop tomorrow.