Batch process- resistive heater overtemperature safety
Batch process- resistive heater overtemperature safety
(OP)
Howdy:
We have a batch process that 'cooks' material in a chamber under high pressure and moderate temperature. The system was built in-house, it uses a few kW of resistive heater bands controlled by a PID unit. Well, the SSR that supplies power to the bands shorted closed, luckily someone was around and noticed the problem.
I was thinking of using a capillary thermostat, similar to the Thermtrol TS series. But I could not find adjustable units in the range of 125-350 degrees C. My thought was to have this set a two coil latching relay to drop AC mains via a contactor that supplies the bands. User would have to push a pushbotton to reset the latch.
Is this a reasonable approach to the issue?
Any ideas of methods typically employed for this scenario?
Is a capillry therostat a good match for the application? We would mount the capillary to the outside of the chamber.
Any leads of some units that operate in the 125-230C sensing range?
Thanks in advance for any feddback and information.
-AnalogKid2DigitalMan
We have a batch process that 'cooks' material in a chamber under high pressure and moderate temperature. The system was built in-house, it uses a few kW of resistive heater bands controlled by a PID unit. Well, the SSR that supplies power to the bands shorted closed, luckily someone was around and noticed the problem.
I was thinking of using a capillary thermostat, similar to the Thermtrol TS series. But I could not find adjustable units in the range of 125-350 degrees C. My thought was to have this set a two coil latching relay to drop AC mains via a contactor that supplies the bands. User would have to push a pushbotton to reset the latch.
Is this a reasonable approach to the issue?
Any ideas of methods typically employed for this scenario?
Is a capillry therostat a good match for the application? We would mount the capillary to the outside of the chamber.
Any leads of some units that operate in the 125-230C sensing range?
Thanks in advance for any feddback and information.
-AnalogKid2DigitalMan
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"It's the questions that drive us"
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RE: Batch process- resistive heater overtemperature safety
Above should read 125-350C sensing range.
-AK2DM
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"It's the questions that drive us"
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RE: Batch process- resistive heater overtemperature safety
RE: Batch process- resistive heater overtemperature safety
The switch's sensor bulb should be IN the process in a thermowell, not strapped to the outside for the setpoint to be 'accurate'. If strapped to the outside of a vessel, the bulb will lose heat on its exposed surface making it trip at a higher vessel temperature than the switch setpoint. When the bulb is immersed in the process or a thermowell, the bulb heats evenly and only loses minimal heat through its capillary.
There are UL (US agency) approved high limit electronic temperature controllers that use thermocouple or RTD sensors to do exactly what you propose - latch off when tripped.
I've used those small digital temperature controllers with a latching relay to do limit control drop-out.
The last one was a Cal Controls unit, but I can't recall which model I used, one of the ones listed on this web page:
http://www.cal-controls.com/products/3300m.php
Maybe they all have a latching alarm relay?
RE: Batch process- resistive heater overtemperature safety
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RE: Batch process- resistive heater overtemperature safety
BTW an electric range (stove) oven thermostat covers that range nicely, cheap too.
Roy
RE: Batch process- resistive heater overtemperature safety
Thanks for the inputs, it looks like a TC with a separate temperature monitoring relay is the way to go. I was initially trying to keep it simple and not familiar with the devices typically used in the field today.
jraef, thanks for the link to the Siemens, it gives me a better lead on what to look for now.
danw2, the chamber is enclosed in a tie-up insulation blanket, but I do agree that the sensor should be in a thermowell for accurate readings.
Our current PID unit does not have latching alarm outputs, regardless I would like the limiting function to be an independant system.
Thanks again for your time and advice!
-AK2DM
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"It's the questions that drive us"
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RE: Batch process- resistive heater overtemperature safety
RE: Batch process- resistive heater overtemperature safety
Roy
RE: Batch process- resistive heater overtemperature safety
-AK2DM
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"It's the questions that drive us"
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