kiln not holding tempature

J

joeyp1971

Joined
Apr 14, 2009
Messages
36
Just got new evenheat and sprung for Rampmaster. The problem is it doesn't seem to hold the set point as programmed. It bounces around to various point all lower than the set point. it does seem to geneally work its way back to the setpoint but the temp still goes up and down on its way there. I would conclude that it's noral if this was just a couple degrees, but sometimes it's down 10-15 degrees below setpoint. never heat treated before, is this normal?
 
I have a Evenheat 13.5" it fluctuates some but only 2 or 3 deg's max, I guess it could depend on thermocouple placement
 
Does it do this "dance" just on its way TO the setpoint, or constantly?
Without knowing more - my first guess is that the PID variables aren't tuned correctly.
Other causes can be line voltage fluctuations, damaged thermocouple, poor connection of thermocouple or heating elements to their contacts.
 
sorry guys, false alarm - it's working fine. i don't know what happened on the test run but i just hardened 2 cpm154 blades and it held steady w/in 1 to 2 degrees of 1925
 
I have made this statement before, but it bears repeating:

A PID is an intelligent device. It has to learn how to heat up the chamber to get to and hold the set point. The first firing will be jumpy as it figure things out. After that it will be better. Setting the parameters for the type of ramp desired and the other variables will help, but the PID will figure things out as it goes. Once at the set point and holding for a while, it should settle down to about +/- 2-3 degrees.
 
Bldsmth is absolutely correct, and letting a new system tune itself is important. Additionally, I would agree that this would be the most common cause of an instability in a brand new system.

However, I would like to expound on what he has said. Not owning a Rampmaster controller I cannot give direct input on its method of control, or whether it continuously will self tune. However, there are many folks here that are using aftermarket controllers such as Fuji, Auberins, Omron, Eurotherm, Fujitsu, Watlow, etc.to control their homemade furnaces and forges. Most of these controllers will not automatically tune themselves, you must use their "auto-tune" function. It is at this point that the "fuzzy logic" takes over and sets the "PID" values to what it computes will best serve the particular situation. If, however, you change your set point by a very large amount, the system can become unstable again and require a new autotune. Secondly, the auto tune PID values are not always ideal, and you may still have either a controller that will overshoot or have oscillation. At this point you will have to manually over-ride and set the PID values.


Best,
Steve
 
I'm using an Evenheat with the Rampmaster digital control. No matter what temp I set mine at, it ALWAYS fluctuates by 10-15 degrees back and forth.
 
Danbo,
I would call Evenheat and speak to technical services, and also refer to my first post. The fluctuations should not be this large.
Best
Steve
 
I agree with Steve,mine only fluctuates about 3-4 degrees.
Stan
 
Agreed. My Evenheat [with Rampmaster controller] fluctuates about 1F to 2F max once I'm stable at temperature, even as I approach 2000F.

--nathan
 
Last edited:
Stan, again I have not used this particular controller, but after having qualified untold pieces of heating equipment, 3-4 degrees is on the OUTSIDE of what I would consider acceptable. Additional tuning should get you to a smaller deviation, if any.
 
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