Micrologix 1400

dhuber · Sep 28, 2010

Hi,

We got a new machine in our plant a few months ago and we have had an issue with one of the output contacts sticking on the output card. It is a micrologix 1400 with a few expanded i/o modules added to it.
One of the outputs on the expanded output card, the contacts keep sticking closed after the output has been turned off.
This card has been replaced 4 times due to not wanting to shut the machine down and the issue keeps coming up.
Is there anything electrically that i can be looking for that would cause this? It is always the same output. We also have another machine in the plant that the guy who made it says it is exactly the same and we do not have this problem with it.

Thanks.

jimfun71 · Sep 28, 2010

How much load is on the output and what is the consumer of the load. I have had many ML outputs stick if the load is too much. Also, solonoids seem to really do a number on the ML relays. I always use an icecube relay between the ML and the device and haver had great luck doing it that way.

Mickey · Sep 28, 2010

What output card do you have? ( complete catalog number)

What is the load?

Do you have surge protection across the load?

Winklehoffen · Sep 29, 2010

I've had a few similar issues in the past with Micro 1000s. We've since starting sticking interposing relays on them and the problem dissappears. As jimfun said, solenoids don't seem to like micro relays.

nwboson · Dec 5, 2010

Sounds like you're getting bit by 'V = L * di/dt'. For any DC output, if it has any inductive load (a solenoid), any time that inductor shuts off, it will oppose the change in voltage by generating a negative voltage spike. Those voltage spikes weld your relay contact together - and they are as reliable as the above equation. So whenever I have a DC output connected to any solenoid, I put a clamping diode on the output to keep the negative voltage from trashing the relay. Interposing relays tend to help because they have bigger contacts, but will eventually go bad too for an inductive load. Phoenix Contact (and many other companies) sells Terminal Blocks with an integral diode - I use them on ALL my DC outputs.

daba · Dec 6, 2010

ALWAYS use a "flywheel" diode when driving an inductive load on DC outputs - even if that load itself is another standard relay.

The induced voltage when the output turns off generates enough current back through the ML output relay contacts to cause them to arcas they open. They will eventually fail, either through them welding together, or the dirty contacts unable to switch a load.

Opto-isolated interposing relays is a better idea, these are not inductive, so will be kinder to your ML.

nwboson · Dec 6, 2010

An opto-isolated interposing relay does NOT avoid the inductive voltage spike since the inductance is in the solenoid and the di/dt is the instantaneous change of turning off the output. So just add the terminating diodes and you'll be gold.

adel1961 · Dec 6, 2010

it doesnot matter how much load , because ofcourse who ever designed the machine followed the rules of designing the loads with outputs , the problem now is the loadon thatoutput got higher due to the age of the machine . so even you add the suppressors as most of the experts said you might got the same thing happening again,so i prefer to change that solinoidor whatever that load with a new one , better than keep replacing the same board.

nwboson · Dec 6, 2010

I was too flippant on my response that a terminating diode will assuredly fix the problem. As others have suggested, this is a function of load current, load inductance and the ratings of your output card. The 1400's 1762 modules have outputs that are rated from .25A all the way up to 7A.

So you need to analyze the load of the offending modules. And if its a solenoid-type load, then the inductance of the solenoid will cause the aforementioned negative voltage spike every time the output shuts off so you MUST install some sort of suppression like a diode. I try to design at least a 2X 'safety' factor for a load so if the solenoid is a 1A solenoid, I would not feel comfortable unless the output had at least a 2A rating. And if you're being very careful, adding an interposing relay is a great way to ensure your customer has a simple-to-replace part in case of failure.

ksr.kroth@gmail.com · Sep 15, 2015

I currently have a micro relay output doing the same. its powering a 0.75 amp 120vac solenoid. I am debating putting a solid state relay between the output and the solenoid. Anyone have a good part #? the AB ones I look at are not factory stock and only rated for 1 amp. I called Phoenix and all they have is one for $174. Ouch! I hate 120vac.
From now on I believe I am going with 24vdc Triac outputs and Isolating them with Phoenix PART # PLC-OSC-24DC/24DC/5/ACT. (5amp solid state plc interface module) This should solve my problem right?

FactoryTalktotheHand · Sep 15, 2015

I'm guessing this is a solid-state output card and the load is too much for it. Those outputs are only rated for 0.5A continuous IIRC. There are also inrush limits to it as well. Solid-state outputs are great for things that have to turn on and off a lot, but you sacrifice Amperage rating to do it. The bad thing about solid-state is that they fail closed, which can be quite unsafe.

What you'll probably want to do is get an interposing relay. Larger relays have much better amp ratings as well as contact life. Plus, when it goes bad, all you have to do is pull it out and plug a new one in. Also, as suggested by others, get a surge suppression device/flywheel diode/etc. for the relay coil. The load may be fine, but the voltage induced back onto the output due to field collapse when it's shut off can damage it as well.

Mickey · Sep 15, 2015

[email protected] said:
I currently have a micro relay output doing the same. its powering a 0.75 amp 120vac solenoid. I am debating putting a solid state relay between the output and the solenoid. Anyone have a good part #? the AB ones I look at are not factory stock and only rated for 1 amp. I called Phoenix and all they have is one for $174. Ouch! I hate 120vac.
From now on I believe I am going with 24vdc Triac outputs and Isolating them with Phoenix PART # PLC-OSC-24DC/24DC/5/ACT. (5amp solid state plc interface module) This should solve my problem right?

It does not matter if the relay is solid state or dry contacts, you still need surge protection across an inductive load.

ksr.kroth@gmail.com · Sep 15, 2015

My surge protection is built into my AB din cables (889V-LA2DBE-5). I did add dry contact relays in between and now i can actually see the arc when they shut off... Maybe I recieved the wrong cables? I did not check that...

ksr.kroth@gmail.com · Sep 15, 2015

Hard too believe though considering I now have 3 machines doing this

James Mcquade · Sep 15, 2015

There are 2 things that I have experienced.

#1 as already pointed out, the load on the output.
If its ac, use an rc type device built into the terminal block to reduce the counter emf. AB and automation direct has those.
If its dc, use a diode terminal block. AB and automation direct has those as well.

#2 The lifetime of the contact output on a Ml or slc relay output card is 1,000,000 cycles, its in their specs. We had to switch to the triac output card on several machines due to the contacts wearing out, not sticking, due to use.

Please note that if you go to the triac cards, I advise you to put a load on the outputs in parallel with the device to keep it turned off when using low resistance loads. You should also train maintenance in regards to the triac cards and what to expect.

james

Micrologix 1400

dhuber

Member

jimfun71

Member

Mickey

Lifetime Supporting Member

Winklehoffen

Member

nwboson

Member

daba

Lifetime Supporting Member

nwboson

Member

adel1961

Member

nwboson

Member

[email protected]

Member

FactoryTalktotheHand

Member

Mickey

Lifetime Supporting Member

[email protected]

Member

[email protected]

Member

James Mcquade

Member

Similar Topics