Heater Fail Detection

Hi everyone,

I am trying to detect whether a heater fails in my glue system. The heater is attached to a steel block with a glue nozzel(s) in it. Each block is considered one zone of the system. My biggest problem is that this zone usually has 6+ heaters in it and only 1 RTD which causes ununiform heat distribution if a single heating element fails. This is bad for my glue application. I also need to monitor upwards of 50 zones which puts a large space constraint on me as I am trying to use as little cabinet space as possible (as always).

My solution is to put a current tranducer in each zone around all of the heaters. This transducer would output an analog signal to a PLC which I could use to monitor the current. If the current decreased to a certain level, I would know a heater failed and I could alert an operator so they knew to check the heaters.


My question is what is the best way to save cabinet space to do this to all 50 zones. If each analog card held 8 inputs, I would need almost a whole rack (assuming the rack held 8 cards) to monitor all of them. I am also looking at using mostly Allen-Bradley/Rockwell products because that is the majority of what my company uses (I believe we have a discount system with AB). Is there a better way to do this for my large application? Am I even going about this in the right way?

Thank you for any help.

P.S. I do not know how the heaters are connected. They could all be in parallel or in a series/parallel combination.

For this type of Application, we use adjustable CTs with a switched Output. We are monitoring the Heaters to make sure one hasn't failed. We are not interested in the exact Current going to the Heater.

The advantage would probably be cheaper CTs, and you could cover your 50 Heaters with three 16 Point or two 32 Point Input Cards.

I am sure there will be other suggested options.

Stu....

Thanks for the quick reply Stu. Do you think you could point me in the right direction to finding one of these adjustable CTs with a switched output? I would be very interested into looking at this option but google does not seem to be my friend for finding these.

I think stu is referring to a Current Transducer, like this:
http://www.veris.com/Category/Current-spcMonitoring.aspx

Jiftim,

What PLC are you using? Is it a ControlLogix? (I noticed that in a different thread of yours) If so does it have e-net or device-net IO?

It so then we might be able to come up with a surprisingly economical solution using Beckhoff remote IO and a power monitoring terminal block.

http://www.automationdirect.com/adc...s_(AC_-a-_DC)/Current_Switches_-a-_Indicators

Those are pretty compact and they offer one with multiple ranges and even time delays, so you could wire in series several n/c contacts and group them into zones to save on PLC inputs.

I am still looking for something more compact, just a 1-pole analog CT only, but can find them so far...

http://www.benderrelay.com/current-relay/

I know I have seen something narrower.

http://il.rsdelivers.com/product/abb/cm-srs11/cm-srs11-current-monitor-1co/6128772.aspx

Jiftim said:

Thanks for the quick reply Stu. Do you think you could point me in the right direction to finding one of these adjustable CTs with a switched output? I would be very interested into looking at this option but google does not seem to be my friend for finding these.

Click to expand...

I don't remember the make and model off the top of my head. I will look for the information tomorrow when I am at work, and post it. That's assuming a quite day, so far, Monday has lasted for two days.

Stu....

If you just need go/no go it would be more economical to use a current switch instead of a transmitter with analog output:

http://www.automationdirect.com/static/specs/acuampacs150.pdf

The Current Switches we have here are made by Greystone Energy.

Model CS-310, but I don't see it on their Web Site.

http://www.greystoneenergy.com/current-switches-and-sensors.php

Stu....

Thanks for the replies and options everybody. Here are some answers from my end:

Alaric said:

Jiftim,

What PLC are you using? Is it a ControlLogix? (I noticed that in a different thread of yours) If so does it have e-net or device-net IO?

It so then we might be able to come up with a surprisingly economical solution using Beckhoff remote IO and a power monitoring terminal block.

Click to expand...

I believe the units have a Logix rack with a ControlNet and an EtherNet card installed.

Tom Jenkins said:

If you just need go/no go it would be more economical to use a current switch instead of a transmitter with analog output:

http://www.automationdirect.com/static/specs/acuampacs150.pdf

Click to expand...

I can't just use a current switch in this case because the heaters pulse on and off as they are needed. Not only that but because not all of the heaters burn out at once, there will still be a current when only one heater fails...it should just be less which means I need someway to monitor the current/load value for changes.

sthompson said:

The Current Switches we have here are made by Greystone Energy.

Model CS-310, but I don't see it on their Web Site.

http://www.greystoneenergy.com/current-switches-and-sensors.php

Stu....

Click to expand...

Thanks for the update Stu. I'm sure I can find something I could use from there.

I'm really looking for an AB solution, though, but all of what you guys have provided me will be good for consideration if I can't come up with an economical AB system (which doesnt appear to be happening at the moment). Thanks again everyone. If you can think of anything else that might be helpful, let me know.

We do have Analog versions from the same company, so they are available.

Stu....

siimilar situation, also zone heating with multiple heating and only one RTD feedback

we use a solid state relay with a built in current sensing unit, this unit gives a relay output, so however many heaters are in a zone, they are wired in series back to one DIGITAL input. what you do with that input is up to you, but in our situation we only alarm, electrician then goes to the panel, has a look at the faulty zone, finds the faulty unit, replaces it, job done.

the nice thing about them is that they have led indication on them, so its easy to find the faulty one.

actually, even bubba can do it without messing it up

http://www.powercontact.de/1-1-Home.html

it is the power controller ip-series

I have used these transducers in the past. http://www.crmagnetics.com/products/CR-417080-P44.aspx

This specific one has 3 independent lines being monitored and 3 individual outputs. Very compact, DIN mount. I use it with an SLC 16 point analog voltage card.

Try these guys for an inexpensive CT. http://phenixcontrols.com/?path=Home/Products/Sensor

I have used them in the past for around $9.00/point.