Non-plc

You need to look for a current sensing transducer or switch. You didn't mention how you are going to monitor the signal, but if you get a transducer it will output a small voltage or current proportional to the heater's current. This signal could then be fed into a PLC or smart relay for analysis. If you're trying to stay away from a PLC, you can use a current sensing switch, which controls a relay directly. They usually have a setscrew adjustment where you can control the trip current. Many brands are available, here is one source:
http://web1.automationdirect.com/adc/Shopping/Catalog/Sensors_-z-_Encoders
 
Would to keep it simple. Something with a relay output would be great. I need to monitor 12 heat zones all are 3 plase. Looking for something that I can tie into a signal light. I need ensure all 3 phases are drawing close to the same amount of current during the heat cycle.
Thanks Terry
 
If it's balance between the phases that you're concerned with, pass all three phase leads through a single CT (current transformer). The resulting signal will represent the imbalance between the phases. This would work with the devices kolyur recommended, or any other CT.

Of course, this wouldn't detect a loss of all three phases at once. For that, you'd need CT's on each phase.
 
ASSUMING you are running all 12 zones all the time.
Use 3 current sensing relays - they have CT built in - cost US $75 ??
Wire to 3 lites - now you know that all 3 phase are in balance
OR which one is out of balance (drawing too little).
Dan Bentler
 
DwalterE said:
If it's balance between the phases that you're concerned with, pass all three phase leads through a single CT (current transformer). The resulting signal will represent the imbalance between the phases.

I'm not a current monitoring expert but wouldn't this only detect a ground fault? I tried this in my shop with a single phase heater and three phase power and got no reading.
 
I'm using 240 volt 60hz. A phase relay won't worh for what I need to do. I need to be able to detect a current deferential.

Example phase #1--25 amps
#2--24 amps
#3--17 amps
Phase # 3 would be the one to trigger the alarm. I do appreciate any info on this issue.
Thanks Terry
 
milldrone said:
I'm not a current monitoring expert but wouldn't this only detect a ground fault?

Thats correct. Current out must equal current in. In the absence of a ground fault or an alternate path for the current to escape without going through the CT then passing three phases through the same CT will give a zero indication. When one phase peaks at I, in a blanced system the other two phases will be at -.3333I and -.6667I. If its not balanced and one phase has a different impedence and is at say -.25I then the other will be at -.75I.
Three phase power can be very complicated to visualize, but in this forum we strictly obey Kirchoff's laws. 🍺
 
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I am wondering about the use of terminology here (or perhaps I'm just confused). The first post indicates induction heating. Post 8 says 240V 60hz. 60hz wouldn't be very effective for induction heating. Are you sure its not resistive heating? Or is 240V 60hz the supply to an induction heating inverter?
 
milldrone said:
I'm not a current monitoring expert but wouldn't this only detect a ground fault? I tried this in my shop with a single phase heater and three phase power and got no reading.
At first glance I thought running all 3 phases thru a CT was good idea. Thinking more on it and demonstrated in your case of a single phase load on 3 phase all the "goes out" currents were balanced by "goes in" current so there was no reading. Would work if there were leakage to ground or some other "goes back" path ie neutral not run thru CT.

Think it will still take one current sensing relay for each phase.

Dan Bentler
 
Alaric said:
I am wondering about the use of terminology here (or perhaps I'm just confused). The first post indicates induction heating. Post 8 says 240V 60hz. 60hz wouldn't be very effective for induction heating. Are you sure its not resistive heating? Or is 240V 60hz the supply to an induction heating inverter?

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

Another example where a better explanation of the process and used equipment would help a bunch. For all I know he has three banks of resistive heaters or 3 inductive heaters.

Worked in plastic extrusion (window frame shapes). All the dies and extruder body were heated with resistive heaters. Screws were heated with hot recirc oil

Dan Bentler
 
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