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Need Opinion about electrical heater

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iqbalan

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hi guys, i'm the new guy in this forum. need your help to give opinion about electric heater.

my plant is using electric heater that been control by thyristor. now the problem is when the operation control and increase the temperature at certain temperature , the temp will suddenly overshoot until it reach high high level trip. we already calibrate the temperature gauge for outlet and it accurate with actual temp. are the problem is related with the thyristor? need help from you guys~ :confused::confused::confused:
 
Is the heating related to a flow process, or something like heating a vat or container filled with a fluid?

Is there adequate circulation or mixing of the fluid with the heating element?

Where is the temperature sensor that controls the thyristor, in relation to the heating element?

Is the fluid that is being heated particularly viscous, like syrup, or is it more like water?
 
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this is the problem of ON-OFF controller ( thermostate or simmillar ), if its possible you can use controller, else you may try to use lower watt heater, it will take much time but shooting will reduce.
 
It may be that heating the target medium too quickly is the cause of the overshoot problem.

What about using a helical coil, constructed of copper tubing, with hot water circulating within the helix. The helix is inserted within the main flow pipe or vat, and is adjacent to the controlling sensor. The temperature of a separate fluid circulating within the coil is controlled externally by the on-off thermostat.

The advantage of this scheme is that the length of the helix within the main fluid is adjustable, allowing extended time for the fluid to be heated before it leaves the temperature control section of the process.
 
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this heater is related with process flow.. when the temperature is below 240degree it can be control but when increase little bit, the temperature will increase immediately. Supposedly the design is 300degree with 6850 n/c nitrogen but right now the just using 2500n/c only. before we also using less amount nitrogen and don't have any tripping. how about the strength of element?is it related?
 
hi guys, i'm the new guy in this forum. need your help to give opinion about electric heater.

my plant is using electric heater that been control by thyristor. now the problem is when the operation control and increase the temperature at certain temperature , the temp will suddenly overshoot until it reach high high level trip. we already calibrate the temperature gauge for outlet and it accurate with actual temp. are the problem is related with the thyristor? need help from you guys~ :confused::confused::confused:

Hi and welcome to the ETO forums! :)

Looking at your initial post here it appears this was a working system that now does not work correctly as it once did?

The overshoot you are seeing could have any number of causes, for example the sensor is not responding as quick as it should or in the case of a new system the heater elements could be over sized for the load they heat. The latter being the watt density of the heating element(s). Also, as members mentioned, the type of control being used, for example On / Off verse maybe PID (Proportional Integral Derivative).

Not sure what you were getting at with the N2? However, when heating a fluid or any medium there are a large number of variables to be considered and any number of them could cause the overshoot you are seeing. You may want to look at the voltage on your heater element and see how it behaves as the process variable temperature approaches and passes through the set point?

Ron
 
As allready mentioned the only way to get good tight control is to use a PID system, we have 2 polymer extrusion machines which have several heaters controlled by thyristors, there is a central system which uses a pid loop to maintain heats very accurately.

Overshoot is caused by various things, it can be minimised by reducing the power of the heater (which slows down warm up), and by putting the temp sensor as close to the heater as possible (this can cause temp inaccuracies depending on the thermal conductivity of the tooling).

Look at your thyristor controller closely it might have a pid system, if its adjustable you could try adjusting the D (derivative), but make a note of the settings to start with, before you do this though try instead of adjusting from one temperature to another do it in stages, ie instead of going from 150 to 250 degrees, go from from 150 to 175, to 200 and so on waiting for it to stabilise inbetween, the gain of your system may be too high to cope with large adjustments.
 
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dr peppers:

That's good advice and it would be the first place to look. Are you using PID control? Is it adjusted properly?

Other things to watch out for is a shorted thermocouple at high temperatures.

Thyristers can latch-up with high dv/dt and snubbers prevent that. In any event, they would turn off when the line goes through zero.
 
The quality of your power supply can also affect the controllers peformance, harmonic distortion can create various problems with different types of control.
Do you have power factor correction units, and do they work, do you get power cuts?
 
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