Heater element monitor

johanf

Member
Join Date
May 2006
Location
Capetown
Posts
6
Hi All,
I need to monitor 12 heaters to make sure that all are in a good condition all the time . If one go open circuit it need to show up as a fault on the PLC. I can only think of using CT's and convertors to analog chanels but this is expensive. Is there any other ideas that i can try.
Thanks In advance
 
johanf said:
Hi All,
I need to monitor 12 heaters to make sure that all are in a good condition all the time . If one go open circuit it need to show up as a fault on the PLC. I can only think of using CT's and convertors to analog chanels but this is expensive. Is there any other ideas that i can try.
Thanks In advance

Are these heaters run under a temperature controller, or are they operated by the PLC? What is monitoring their temperature?

Dependant on your reply you could monitor time after switching on heater until it reaches set point. Can you give us a little more info on the 12 heaters, eg are they independantly controlled heating independant objects, or what?

I am sure some temperature controllers can be set to monitor load current also.
 
If they are stand alone heaters then the way you describe is one way, another is temp probes back to analogues.

Is there a device that can read the CT current and send a digital signal?
 
Hi all ,
Sorry about that. The haeters are all in one big water tank to generate steam. I will monitor the tank temprature with a pt100
so i can not use the temprature rise of idividual heaters as all will have a influence on the water temp. The custumer want to know if a element is out (and witch one) as this will take longer to get to the desired temp.
 
johanf said:
Hi all ,
Sorry about that. The haeters are all in one big water tank to generate steam. I will monitor the tank temprature with a pt100
so i can not use the temprature rise of idividual heaters as all will have a influence on the water temp. The custumer want to know if a element is out (and witch one) as this will take longer to get to the desired temp.

rdrast's link looks good. You could send a digital signal to a PLC or just illuminate lamps (when healthy maybe the best)
 
There are Current monitors available that can supply a 24VDC or a 120V input. Look in the MSC or grainger catalog for a few cheap ones. I have used these in the past many times, monitoring secondary plastic melt trimmers.

Put a timer in your program that looks at an input every minute or so. In your logic, put an AND statement (XIC_XIC) for the output firing the heater element with the input from the current monitor. This is easy.
 
as peterw correctly suggested just insert some lamps in series with your elements as theres no need to let tne PLC know an element has failed i would have thought it would just want to know the process is running at the right temperature
 
One point was not addressed, are the heaters 3Ph or 1Ph? If 3Ph then you would need one on each phase of each heater.
 

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