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MalSnaize

IO-R08 Relay Module - Output LEDs

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Hi there I have a simple question about IO-R08 module output LEDs.

I have a V700 with attached expansion and IO-R08 modules. The intent is that the relays will pulse process pumps at up to 9Hz during scheduled and manual sessions,

Everything appears to be working, however I am about to deliver to the customer to install with the pumps and i notice an odd beahviour of the output LED indicators  on the relay module.

When I pulse the relays, the LEDs pulse - but inconsistently.

If I pulse at, say, 1 to 3 Hz the LEDs appear to be pulsing at the same rate but as I increase frequency up to 9Hz the LEDs appear to have a more random nauture to their relationship to the actual relay frequency.

Should the LEDs represent exacly what the relay is doing, partcularyly at the upper end of their range - 9Hz? See short vid of all relays firing at 9hz - the output LEDs dont fire consistently.

 

any thoughts or guidance greatly appreciated.

 

Thanks, Mal
 

IO-R08 at 9Hz.MOV

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I really don't think using relay outputs at 9 Hz is a good idea.  This is a transistor output application. 

I think what you're seeing is the latency of the relay module response trying to keep up with the scan time of the PLC.  The specification of the relay module is 10 ms response with a 100K  cycle lifetime at maximum load (3 amps).  You did not specify your actual load current.  If your load is inductive (a solenoid) you have to take into account the flyback pulse which will add to the relay contact point degradation.

You didn't say what your duty cycle is, so I'll guess it's 50%.  The ON time of a 9 Hz signal at 50% is 55 ms, for a 111 ms total cycle.  So if you're cycling relays at this rate and you go 100,000 cycles then you have 11,100 seconds before you hit the "rated" life.  That's 185 minutes or about 3 hours.

Usually relays go longer that their rated life because of less load, but that can go out the window if you're pushing solenoids, contactors, or even other relays.  So let's say you get 1 million cycles.  So now we're at 30 hours of operation be things start failing.

I speak from experience and I'll bet that module doesn't last more than three months.  I always use transistor outputs with those 6mm individual TB-style relays now.  It adds cost, but when one fails it's an easy and cheap fix.

Joe T.

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Hi Joe many thanks for your feedback.

Thats a bit of a blow! I was advised to go down this path but your analysis and advice cerftainly stacks up to show thats not the case.

A bit more info (which wont help but's for interest) -

  • Yes we are switching solendoids - the chosen process pumps are air-driven with internal solenoids. (I do have protection diodes across the load)
  • We haven't finalised the duty cylcle/frequency combination as we need to test in-situ and try varying models - centralised pumps  vs distributed pumps.
  • Higher air pressure vs higher frequency (I think the higher air-pressure is the way to go).

All of this will help us assess what freqency and duty cycle we pump at to get the various flow rates we need.

The only saving grace is that the pumps wont be running 24/7 and scheduled to run certain times of the day.. Still, I think I'm going to have to swap out to transitstor outputs - I hope the module fits!

Thanks again!

 

cheers Mal

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+1 on all Joe is saying.  Relays are not suitable for this.

And a word of caution on top of Joe's talking about the TB-style, they are great, but I have found you have to be careful with their ratings.  Specs might read 3A @ 240V on an SSR, for example, but in fact when you dig further into the details you discover that the thing is only rated for a maximum power as well, often far less than is initially implied.   I have been caught on this, couldn't understand why units were failing.  And discussion with the manufacturer didn't yield a suitable explanation of this conundrum.  Very very fine print stuff, read it all carefully during choosing.

cheers,

Aus

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Thanks Aus - your shared experiece much appreciated.. I'd hate to go back to my client with a change which in itself fails in short time.

I have a meeting with them today and will have a better idea of the exact usage and will go back to my local distributer for further guidance.

Actually general question: Is it appropriate for me to spell out the exact spec of pumps etc on this forum and ask for suggestions on best module to use?

Cheers Mal

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Definitely OK on specs of things.  Putting up your product for sale....perhaps not!!

Often it is easier to quote a web address of the relevant manual.  Interested parties can then dig down into everything possibly needed, thus saving problems/time.

cheers,

Aus

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Hi Again so here's a bit of an update:

My provider agrees that perhaps the IO-R08 relay module is not the best option and recommends a solid state module.

The pump I am switching is an SMC PB1011-A (see attached spec extracted from manual) and I'd be keen to get others' views to confirm that the IO-TO16 will do the trick?

Note the pump has a built in solenoid and that is what I am switching at 24V.

Thanks in advance of any advice.

Kind regards

Mal

PB1011A Spec.pdf

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The spec says the pump draws 0.35W at 24V.  Without seeing one, I'm guessing these things are small. 

That translates to a 14 mA draw from the PLC output.  The IO-TO16 has a 0.5A rating per point, which can handle this easily.

Joe T.

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Hi Joe thanks for your advice.

yes they are quite smal phyricallyl but are spec'd to move 2L / minute which is great for the application.

I' m quite relieved as the alternative would have been to add 8 solid state relays to drive the pumps which would have been a significant increase in cost.

Good outcome!

Kind regards

 

Mal

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Hi guys,

 

I usually use this type of transistor board to isolate the PLC outputs from the controlled load.

It can switch 3A per channel with 1KHz switching  frequency while current draw on PLC output is a few mA.

For the 10 channel board, the cost is something like 17 USD.

 

It's significantly cheaper than using relays and requires much less wiring.

 

plc interface board.PNG

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7 hours ago, Kikis said:

I usually use this type of transistor board to isolate the PLC outputs from the controlled load.

Looks interesting. Can you provide a link to the product?

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Ah, AliExpress!  Explains the $17 price tag.

I've bought some stuff off this website and haven't had any problems.  Just don't be in a hurry to get your stuff.

Have you had issues with the product being available and then disappearing into the Ether?  I had that happen on a Bluetooth receiver board I put in the old radios I restore.

Joe T.

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I've used the 16ch relay versions in the past to drive 24VAC components without any issues.  Supposedly fitted with Omrons, and certainly looked genuine but who knows.  These days Aliexpress has far more range of stuff in this regard....like Kiki's example.  The one thing that I was worried about was they seem to like using MOVs on AC stuff.  But still going fine, oldest in use is 4 years.

I buy from there regularly.  Generally shipping arrives to Aus within 3 weeks.   I am wary of using my personal payment cards on their systems.  I have a dedicated "no-name, top-up as needed Visa" I only use there.  Never had any issues anyway, but I don't mind those numbers being stored on their system as it hasn't anything in it until I need it!

cheers,

Aus 

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Hi Guys,

 

From my experience, one should be careful when buying something from AliExpress.

Especially when buying stuff to be used in control panels for machinery and other critical equipment.

It's always a good idea to communicate with the seller before placing an order.

The site is full of cheap Chinese copies of products which look 100% original (for example, SSR's).

However, it is a safe site to buy stuff and i never had a non received order. Also never had any problems with my Visa Card.

 

Regarding the transistor boards, i use them in almost every project since i discovered them last year. They do the job without any problem at all.

Delivery time (Europe) is approx. 1 month. 

 

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