Simple PLC Replacement

Trying to do a real simple job, where i have 8 inputs coming in (Auxiliary for 8 Fans). Need to confirm at least 5 are running, and turn an output on if they are.

Just need something basic, but reliable enough. Any suggestions ?

You could use a click PLC for $69. from Automation Direct. Software is free. I have used enough of their PLCs to say that if it works the 1st time, it should continue on for years. Personally, i would spend a few pennies more and use a Micrologix 1100. for me, it would be easier and faster since I would already know the software. Both of them have enough I & O for your application.

Or are you looking for a simple circuit to be used instead of a PLC?

bernie_carlton said:

Or are you looking for a simple circuit to be used instead of a PLC?

Click to expand...

That would work too as long as it is good for 120VAC.

Then this Click - 8 AC in $79. Free software. Cable from 9 pin serial port $14. Cable from USB port $43.

A little more expensive than what you have been given, but I will offer up to you the TriPLC FMD series.

http://www.eternity-sales.com/tri-plc/fmdseries.htm

Whether for this application or for an upcoming application, the combination of digital and analog I/O in combination with Ethernet makes it an attractive solution.

If the logic is as simple as you mentioned, I'd just use a smart relay. You wouldn't even need programming software; just configure the logic on the LCD. Allen-Bradley Pico, Telemecanique Zelio, Omron ZEN just to name a few.

Just need something basic, but reliable enough. Any suggestions ?

Click to expand...

Here is a very basic 6-rung Automation Direct CLICK program.

How about clearing a register, 8 conditional adds of '1' and a test of register greater than or equal to 5. Thus evaluated every scan.

bernie_carlton said:

How about clearing a register, 8 conditional adds of '1' and a test of register greater than or equal to 5. Thus evaluated every scan.

Click to expand...

Something like this, Bernie?



-Eric

Thanks for the help guys. Appreciate the help. Not quite sure how you would program that with a smart relay but i will look into it.

Yea i have used logic just as bernie suggested. Have used it in AB PLC in the past, but the example for Click makes learning the instruction set simpler.

Appreciate the help. Not quite sure how you would program that with a smart relay but i will look into it.

Click to expand...

I can't see how Eric and Bernie's great logic could be made to work with a smart relay (which normally has no available memory storage registers, move, copy, or math instructions).

But my version will fit nicely into a Omron ZEN smart relay, like the attached file. Running the ZEN simulator, the Output Q1 stays on if 5 of the 8 fan inputs are on. If there had been 9 fan inputs, then the ZEN could not handle the job because it only has 16 comparison "relays" P0 to P9 and Pa to Pf. I could see no way to do each timer value comparsion with only one <= or >= (the only two comparison instructions available). Each input pulse must have some time between it and the previous one, so that the pulse relay will go off, then back on, causing Counter 1 to count from 0 to 5.

I used 2 ZEN expansion modules to get the 8 fan X inputs, but you could use the remaining 4 built-in inputs and 1 expansion module. The ZIP file is the actual ZEN program.

Lancie1,
I've been trying to figure out a solution using only relays and contacts programming but it gets too confusing.

Instead of using a timer could you use false for the Counter on every other rung?

Siemens implementation example: