Non-plc

[Brian123]

Me too, all the induction heaters I've worked with generally run in the khz or MHZ range.

60Hz induction heating is used, but it's not as common as the higher frequency. 60Hz is used more often when you are wanting to do bulk heating (such as billet heating). Higher frequencies are used more often when you want to selectively heat the skin of the part. The depth at which the heat is generated is inversly related to the frequency of the power.

Some examples of low frequency applications:
http://www.inductoheat.com/induction-low-frequency-heating-applications.php

As a side note, I have seen an ad for a machine that used DC power to inductively heat billets. The DC was used to setup a magnetic field in a superconducting coil (cooled with Liquid Nitrogen) and they rotated the billet in the coil. Pretty cool, and they claimed it was more efficient than regular induction heating.

Edit: I do agree with the others though; resistance heating would be much more typical for a plastic extrusion application. To the OP, what are you using to control the power to the heaters? Some controllers have the capability to monitor the balance of the three phase current.

Brian

 

[DwalterE]

That's correct, if the heaters are connected in a delta configuration. (ie no neutral lead). If they're connected in star, with the neutral taken back to the supply neutral point, the single CT stunt will work.

 

[Brian123]

That's correct, if the heaters are connected in a delta configuration. (ie no neutral lead). If they're connected in star, with the neutral taken back to the supply neutral point, the single CT stunt will work.

If that's the case, you could just monitor the neutral leg for current instead of shoving three power condutors through a CT.

Brian

 

[DwalterE]

Yes. That would also work.

 

[RDS]

You might try these guys:
http://www.phenixcontrols.com/?path=Home/Products/Sensor/Current&ga=1&gclid=CNvmyue7wZECFRE9Igod6TL7OQ
I bought some for a wastewater project but haven't installed them yet. I am using them for a PLC input, but you could just as easily operate a relay or indicator light. Many versions to choose from, some quite inexpensive.

 

[milldrone]

Terry,

As you can tell there are plenty of people who want to help but we need some answers to the questions we have put forth.

 

[Lancie1]

1. Would to keep it simple.
2. Something with a relay output would be great.
3. I need to monitor 12 heat zones all are 3 plase.
4. Looking for something that I can tie into a signal light.
5. I need ensure all 3 phases are drawing close to the same amount of current during the heat cycle.

Okay, so you want a current sensor with a relay output. It must monitor each phase separately, so you will need 3 current sensors on each 3-phase heater. I have used the Universal AC Current Sensor from Graniger.com (see link below). It can do all the things you mentioned, for up to a 20 Amp circuit.

http://www.grainger.com/Grainger/wwg/productIndex.shtml?from=Search&newSrch=yes&operator=keywordSearch&search_type=itemnum&action=Go%21&QueryString=6c057&submit.x=0&submit.y=10