Digital I/O on SC-2345 terminal block

[BER1]

I have connected 4x reed switches on a 24v circuit into digital inputs P0.0 to P0.3 on the terminal block of the SC-2345. The switches are properly grounded but for some reason I am getting flickering signals from them, monitored through Labview programme, even though they are no where close to being made (when they are made I do get a normal input signal). Any ideas anybody? 

[JamesC]

Hi BER1,

What device do you have the SC-2345 connected to? When you say you are connected P0.0 - 0.3 do you mean on the screw terminal block inside the unit, or are you using an SCC DIO module? If so which one?

Regards
JamesC
NIUK and Ireland

[BER1]

Hi. It is the screwblock terminal.

[JamesC]

Hi,

What card inside your computer is the SC-2345 connected to?

Regards
JamesC
NIUK and Ireland

[BER1]

It's a PCI-6251

[JamesC]

Hi BER1,

Can you try putting a 120-500ohm resistor between the port line and digital ground.

Regards
JamesC
NIUK and Ireland

[BER1]

Hi. That seemed to stop the problem. Do you think I should be using a SCC-DIO1?

[JamesC]

Hi BER1,

You now have a system that works. The addition you would get with the SCC-DIO1 at this point is system isolation, if one of the reed switches broke down and put the 24 volts in to the DAQ card, this should be stopped by the isolation on the SCC module, and that would be the only part of the system to potentially breakdown.

Regards
JamesC
NIUK and Ireland

[BER1]

Thanks for your help..

[BER1]

Hi JamesC

Unfortunately, I still have a problem! The flickering issue is now solved but now the resistors are overheating, I started with 0.25W resistors and they started smoking! - I have since tried 2W resistors and am having the same problem. Any suggestions, thanks.