Controlling temperature of heater wire.
Controlling temperature of heater wire.
(OP)
I wish to run a Nichrome heater wire nearest to its maximum temperature and with a high watt density. I am concerned that when heated body which is a steel block attains maximum temperature traditional temperature sensing may be too slow.
I am currently using thermocouple with on/off control. I know a PID would be better.
Is there a control method to directly sence heater temperature fast enough to prevent heater burn-out at 900C ?
I am currently using thermocouple with on/off control. I know a PID would be better.
Is there a control method to directly sence heater temperature fast enough to prevent heater burn-out at 900C ?





RE: Controlling temperature of heater wire.
You have to define what the ragged edge actually is. Once you have that, then you need a sensor that can give you an accurate value. Then, you need to act on that sensor value quickly. And so on down the line. When it comes down to it, a PID (or similar) is your best bet... but if you're running at the ragged edge, you'll need to do some real fine tuning to make sure you don't go beyond that edge.
Why the need to run right at the edge?
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Controlling temperature of heater wire.
Perhaps a colour sensor?
Benta.
RE: Controlling temperature of heater wire.
Cant use optic sensor. Device will be enclosed.
RE: Controlling temperature of heater wire.
http://wiretron.com/nicrdat.html
Nonetheless, speed of temperature sensors should not be an issue: http://www.omega.com/prodinfo/TC_Graphic1.HTML
TTFN

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RE: Controlling temperature of heater wire.
On the temperature probe issue. The speed of the probe is not in question. I am concerned that given the temperature of surrounding material (+900C) if heater is given full power the probe will have to be incontact with heater wire to regiser its temperature rise in time and this would be fairly difficult in a compact system.
In a cartridge heater the hot junction is usually at the tip. Heat might have to travel from heater wire through ceramic and MgO powder with only a temperature gradient of only 50C. I would like to reduce this responce time and get finer control.
Thanks
RE: Controlling temperature of heater wire.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Controlling temperature of heater wire.
So, one can easily imagine using a 50°C lower setpoint until the temperature stabilizes, and then slowly ramp the temperature up. Since all the behavior is deterministic, it's a matter of characterizing the "plant" that the PID is driving and including the response profile into the PID programming. This is something that needs to be done, regardless, although other systems might not need such complex startup. Given that you know you have lag, your PID has to be tuned accordingly.
I should point out that 50°C is probably as close as I would want to get to the spec melting point anyway, since the melting point is dependent on the exact composition of the nichrome, and nothing is ever made identically the same.
TTFN

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RE: Controlling temperature of heater wire.
Keith Cress
kcress - http://www.flaminsystems.com