5 VAC With Micrologix 1000

iadapt

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Join Date
May 2012
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Hey guys,

I am trying to just use a level sensor probe and connect it to a micrologix 1000. The sensor is powered with 120 vac but it sends 5 vac as a signal.

Thoughts?
 
Is it a Digital signal or Analog? 5Vac is a very strange output!! Are you sure the unit is not outputting a signal and you are picking up some leak or stray voltage?

If its Digital you might have to find a interposing relay that has 5VAC coil to make it work.
 
Drive an optoisolator with one of those little power supply bridge rectifiers (or build one from scratch) and hook the optoisolator output to your input. You'll also need a few resistors.
 
Bullzi, I am trying to create a work around for a process technology level sensor.

http://www.processtechnology.com/pdf/LC.pdf

I would love to just go from a sensor to the PLC. But I have a process that has fluid at 190 degrees and I cant find a level sensor that can REALLY stand up to the heat. Except these sensors. But the cost to replace every sensor on my line is $20K plus.

So the reason for my attempt to create a workaround. DougP and Firejo, those are great ideas I will work on coming up with something that will work using your input. Thanks guys!
 
After seeing Firejo's post, and since you mention multiple sensors I'd go that way. Off-the-shelf, DIN rail mount, part number configurable - what's not to like?

Depending on the number of sensors there could be an issue with panel space.
 
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I think you are misinterpreting these level switches. The fluid shorts and trips the sensing relay, which in the case of the unit in your link has a SPDT relay contact. You can put any voltage you want on these contacts.

Or am I misinterpreting and you are trying to go right from the electrodes to your PLC. Not usually a good idea!
 
With Tom here on this one, the link the OP provided looks like they're simply discrete level switches. iadapt, you'll have to confirm if they're giving an analog output (0-100% of level) or simply firing an output relay as Tom had described.
 
I was thinking the exact same thing Tom. That is just a level switch that work off the conductance of the liquid. You should be able to use the relay to send you a signal when the level is hit.
 
Bullzi, I am trying to create a work around for a process technology level sensor.

http://www.processtechnology.com/pdf/LC.pdf

I would love to just go from a sensor to the PLC. But I have a process that has fluid at 190 degrees and I cant find a level sensor that can REALLY stand up to the heat. Except these sensors. But the cost to replace every sensor on my line is $20K plus.

So the reason for my attempt to create a workaround. DougP and Firejo, those are great ideas I will work on coming up with something that will work using your input. Thanks guys!

Where do you see 5 vac in the pdf you posted.

I see 14.5 vac, why don't you want there electronics and use it to interface with your PLC?
 
The original is a relay switch so that is easy.
If you want a new setup you will need to make electronics, and yes it can be done. a way to do this to lok at a levelsensor electronics, it is not complicated, and it only needs a conducting liquid.
It consists of a oscillator and the pins.
if the capacity changes it is detected by the electronics.
 
The reason I dont want to use the electronics is cost. I can achieve I hope the control I need with a micrologix 1000.
 
The reason I don't want to use the electronics is cost.
If you DON't use the electronics and relay that is made to work with the level probe, you will end up with costs up to the wazoo! Trying to fix a jury-rigged cobbled-up system is always more expensive than doing it right at the beginning. Most likely, the level switch electronics has a timed decision circuit that decides when or if a varying or intermittent conductivity is showing the true level. You will have to somehow reinvent that in your MicroLogix 1000 program (reinventing the wheel that you decided not to buy to save on costs). The ML1000 analog inputs are not very high-resolution, so that is a strike against your plan, plus you only get about 2 analog inputs per ML. To make it work without the factory electronic control package, you will have to duplicate the impedance of the circuit, convert the 14.5 VAC signal to a 0-10 or 0-5 volt DC signal, hope for the best, and spend many hours reinventing what Process Technology spent years developing.

Don't waste your time and your company's money.

Using the Process Technology factory level switch probe with electronic control and output relay, you only need wire that relay contact to a digital input on your PLC (whatever type it may be). No analog inputs would be required.
 
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Totally agree with Lancie.

Buy the relays - they are inexpensive compared to destroying your analog inputs when power disruption causes your cobbled together VAC supply circuit to exceed the voltage you've estimated.

I have come across systems like this in the past, and when they are not working then what usually happens is they get biffed out and replaced with a professional installation (simply because the engineering time to figure out what you were trying to do exceeds the cost of the parts!) . Not only does the customer have to pay twice, but your name is mud afterwards.
 
Hello Lancie & Saffa, I guess I have to chalk this one up as a loss. I did spend some company money. I did have to retract too using a system that is similar in design and cost to accomplish the controls I need.

BUT- here we go ---- Only because the stinking level floats cannot take the heat form our process.

That's it. This was a solid plan until I discovered that the only floats that work are the type that was originally installed. I usually have no problem just replacing original equipment.

But I did everything I could to get the original equipment to work. With no luck. I brought in an Engineer, another electrician and my guys worked on this as well. The controls just wouldn't stay working.

SO I am ordering some new electronic controls and level probes and I'm going to get them working asap. Thanks so much for your help.
 

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