Problems with I/O Module: IO-DI8-RO4

[RicksinSD]

Good morning to all, I'm I&C tech here at my plant, and we have been having problems with these modules, so far 3 modules have been needed to be replaced. The issue with them,  is that some of the output channels do not change state even when the status LED does. we have removed power to the module in order to "reboot""reset" and they start working again, but as time goes by,they go bad again. Could our problem be external to the modules? Our set up is:

 

HACH sequencer>EX-A1>IO-DI8-R04>IO-AI4-AO2>IO-AO6X

 

The loads for the DI8-R04 are 120vAC solenoids and they do not have the RC snubber, if we need to have them, any recommendations on which to buy/use? Thanks.

 

[AlexUT]

Hi RicksinSD,

It seems, that solenoids, when disconnected, produce arcs on relay contacts and generate EMI, which stops internal module processor.

You have to power cycle it to return to regular work.

 

You have to use snubbers or other protection circuits for 2 reasons:

1.Protect relay contacts - suppress arcs.

2.Minimize EMI.

We have no specific recommendation not about snubber type, nor about snubber manufacturer.

You have to choice it in accordance to load type and other parameters.

Each snubber manufacturer have its recommendations, in formulas or in tables.

I hope this helps.

 

As well, you have to check modules grounding.

There is document "System Wiring Guidelines" in Support->Technical Library

http://www.unitronics.com/Downloads/Support/Technical%20Library/Technical%20Notes/System%20Wiring%20Guidelines/General_Wiring_Guidelines_SUPP-DOC_10-13.pdf

[cantcliff]

I recommend terminal blocks with a flyback diode, or add a flyback diode into the wiring as well.  Anything generating an inductive load could cause a back wards current into the module, which can also damage the contacts.

 

*edit*

 

Sorry, missed the AC signal portion of the discuss. 

[RicksinSD]

Hello there, thanks AlexUT for responding to my post, just Today I have added snubbers to the solenoids, I'll report back if anything happens again, and the link was helpful to me too.