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Ok so the operatives at work are wining about how hard their jobs is, the usual.

The scenario is at the moment they have a set of vibrators on dust silos that feed onto a conveyor belt, the current set up is an on/off switch on the control desk that switches the vibrators on via a contactor. The problem being they forget they have switched them on and if the belts running slowly it just compacts the material in the silo and causes a blockage. They've been told that they are only to be used to clear a blockage not all the time, but you know what there like.

What I'm after is a relay that once energised will close for a set time and then open for a set time and repeat whilst it has power to it. (hope this makes sence). This way when the belts running slowly it'll still have chance to run out of the silo before settling.

I have worked a control circuit out using a couple of omron timer relays I'll upload a drawing when I get to a computer, there is 12 silos I'll have to convert to running like this, so I was wondering if there's a one off unit that will do the job just to work out and see what the costs will be for each option. If there is such a thing i'd only need 12 of them rather than 24 timer relays.

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  • Thread Starter Thread Starter
  • #2
Hi you could try RS part No 385-6935
(LI) Asymmetrical recycler pulse start.
Apply power to timer. First transfer of contact occurs as soon as power
is applied. The timer now cycles between ON and OFF as long as
power is applied. The cycles are not equal (time off = time on).
So at 12 units going to be over £600 why not look at a Schneider Zelio unit SR3B261BD with SR3XT61BD these unit can be programed
with little or no knowledge of PLCs cost around £200, ask your schneider rep about starter packs these include cables and software
I have used them for over two years now and would not go back to using timers and relays for this type of control


Pulse timer relay... you can probably get a multi function relay that might have the option too but loads off them out-there over the differing brands.
Just be cautious you fully read the functions and understand them as they can be tricky to follow at first when your searching for one.

You could choose from a permanently energised relay which waits for a signal which sets a pulsing on off action at desired time settings.
You could choose a timer that operates on and off pulses only when energised..this been your probable best option.

Look up timer relays if you just put relays you wont probably find what your after.


As Duke saysif this is all one machine then a plc the way to go but if individual control systems then a pulse action timer relay between switch and contactor is cheapest option and shouldn't take 5mins to set up.http://docs-europe.electrocomponents.com/webdocs/0fab/0900766b80faba48.pdf


first link check out the symmetrical flashing option bottom page 4 and funtion diagram top of page 5

2nd link £35 + vat cant go wrong at that but i stress check the function option is what your after the Key to the symbols is at the bottom of the link.
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  • Thread Starter Thread Starter
  • #7
Although I like PLC’s in this instance there’s no need. One relay can control all the feeders.


  • Thread Starter Thread Starter
  • #8
Cheers for the input guys.

Theres no room in the control room to fit another plc it's massively cramped as it is. I try and stay away from using them out on site, even with ip67 enclosures after a couple of years in the environment there in they get crap inside them. Plus doing it this way if a relay fails it will only effect one silo rather than all of them.

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