I need help to detect an AC burned heater element

[igeorge]

Hello,
I need help to achieve a very difficult task for me.
We have in the plant few machines for welding plastic, based in heating plastic and pressing the parts together.
The company which made them is out of business so no luck there.
Each machine run at 110 VAC, and has almost 100 heaters.
The heaters are from 250W to 450W, and are controlled by a SSR and a heat controller which fire them at different phase angle to control the amount of heat.
The issue is that they burn out, one, or more and is hard to detect it without manual visual inspection of each part.
My task is to find a solution to detect if any heater in the machine is burned out.
I started by looking at ACS712 from allegro micro. It seems to be good , but i have a problem - ANALOG
The chip give out 0 to 5 volts with middle point at 2.5 volts for zero amps. Amps in the positive side goes 2.5 and up, and the negative side 2.5 and down.
So the output, at any amps reading is a sinusoid at 60 HZ.
For my point of view, all i need is to get a digital 0 or 1 for the result, so i can input it to a PIC.
0 if the current is under 1 Amp, and 1 if it is over 1 AMP
As i mentioned before i do not have a clue about analog, op amp to condition , or amplify the signal, or the rest. I just know plain basic of analog.
Please help , and if you have a solution which you believe it will works, a small drawing, even by hand but with component value will be great.
Thank you

[Gevo]

Hello,

Maybe someting with a magnetic (Murata AS-M15TAN-R) sensor ? This give you a 5-volt low/high signal when detect a magenetic field.

Regards,
/ Gevo

[Archangel]

Hello igeorge,
Could you elaborate a bit on the conditions you want to test the device? It seems you want / need to test during the welding operation. Can you install a tiny reed switch along the power wires? Honestly I do not know if a reed will activate on an A/C load wire, a coil like a Tape Head or a guitar pickup will. If you do not need to test during operation, then a simple continuity test should work, neon lights used to work very well for that.

[igeorge]

Thank you Gevo for suggestion. I have to test it first because i do not know the value of magnetic field at 10 amps.
I will update you when i get it

[igeorge]

Hello igeorge,
Could you elaborate a bit on the conditions you want to test the device? It seems you want / need to test during the welding operation. Can you install a tiny reed switch along the power wires? Honestly I do not know if a reed will activate on an A/C load wire, a coil like a Tape Head or a guitar pickup will. If you do not need to test during operation, then a simple continuity test should work, neon lights used to work very well for that.

Thanks Archangel for reading my post and offer to help.
Here are the conditions:
I must check during the weld process, and i have to make sure that the current going through the wire is over 1 amp.
I do not think the other solution is feasible, due to the number of wires involved.
What i have in mind is to have a PCB for 16 heaters and bring the wire heater to it to one terminal, run a trace through some device to get the current, then get out on the next terminal and go to heater.
Current transformers is not a solution, as they are bulky, not to many models PCB mount and i still need to interpret the reading.
My option was for ACS712 , but if you look at the attached graph you will see that the output is + and -
I need somehow to convert it, or do something that i will get only the + portion, but not pulsating, i need it as a continuous line.
Also, i need that any voltage over 2.6 volts to be a logic 1 and any voltage from 0 to 2.6 to be a logic ZERO. In this case, i will have my inputs to PIC set to read 1 for a good heater, and 0 for a bad heater.
Thank you

[Archangel]

Thanks Archangel for reading my post and offer to help.
Here are the conditions:
I must check during the weld process, and i have to make sure that the current going through the wire is over 1 amp.
I do not think the other solution is feasible, due to the number of wires involved.
What i have in mind is to have a PCB for 16 heaters and bring the wire heater to it to one terminal, run a trace through some device to get the current, then get out on the next terminal and go to heater.
Current transformers is not a solution, as they are bulky, not to many models PCB mount and i still need to interpret the reading.
My option was for ACS712 , but if you look at the attached graph you will see that the output is + and -
I need somehow to convert it, or do something that i will get only the + portion, but not pulsating, i need it as a continuous line.
Also, i need that any voltage over 2.6 volts to be a logic 1 and any voltage from 0 to 2.6 to be a logic ZERO. In this case, i will have my inputs to PIC set to read 1 for a good heater, and 0 for a bad heater.
Thank you

Ok so I am thinking, use 2 diodes in parallel with their polarities reversed so there is a path for both phases, then only run the forward phase through the device.
0 amps = 2.5v 1 amp or more, is above 2.7v.
What do you think, will this work?

[Pic_User]

Hi igeorge,

If you just need an un-calibrated “Go - No Go” measurement, a simple “peak detector” could work.
If a silicon diode has too much junction drop, maybe a germanium or Schottky diode would work.
Just a diode to a capacitor circuit on the output of the ACS712.

-Adam-

[igeorge]

Thanks Archangel,
I do not know if it will works, but i will try it. I am some how concerned about the power dissipation as they are 5 amps going through the diodes, and they will be 32 on one PCB for 16 heaters. I will test and let you know.
Thanks again
Ion