Rate does not match program

[Marilyn T]

I programmed a C6DHSC program into my Skutt 1018 and the rates matched except in Ramp 3 which I programmed in for a rate of 108.  The reading when I pushed the "5" key, which shows the programmed rate of rise per hour showed 120.  I pushed the review button and it showed a rate of 108 in that segment.  The 120 reading showed all the way from 2100 to 2200 and into the 10 minute hold. The rest of the rate readings are in line. This is the first firing since I changed the relays, elements and thermocouple.  The previous ramp 2 had a rate of 350 (in my kiln 344).   My amp reading reads 20 for both;   This is not my normal firing schedule so I don't have a comparison from an old firing.  My guess is that the kiln couldn't cool down from 344 to 108 quick enough but that doesn't explain why the rate didn't decrease over the 2100 - 2200 range.    Any idea why this happened?   Thanks.  

 

 

Edited April 27 by Marilyn T

[Bill Kielb]

If I understand this, you programmed for 108/hr and actual firing it achieved 120/hr.  Further you programmed 350/hr and it actually achieved 344/hr. My initial thought is it was operating at the Precision it could. In the 108/hr segment (more overshoot in the algorithm) and in the 350/hr segment maybe a combination of what it could achieve power wise and undershoot in that segment. So my initial thought is many times programs do not fire perfectly at the rate programmed. Quite often when rates are programmed that exceed the actual power available they really go a lesser rate. How well a controller matches temperature throughout the firing is dependent on several programmed characteristics in the controller. One would be relay cycle time. My experience, kiln controllers do a pretty nice job of matching the kiln characteristics so those actuals would not alarm me. It would tell me though for that loading, you don’t quite have enough power to maintain 350/hr, very close though and you have enough power to maintain 108 degrees per hour in the final segment.

The final segment to me is most important as that is where you are providing significant heatwork to match the Orton columns of maturity. Orton says this starts 200 -250 f from the desire peak temperature (in the Orton chart) The ten minute hold, Ireally can’t speak to, maybe you were trying to drive this 1/2 cone higher.

People have all kinds of schedules that work for them, often very different and much more complex than just following the instructions In the Orton chart. The big question to me is did it fire to the cone you were seeking?

Edited April 27 by Bill Kielb

[Marilyn T]

Thanks for your reassuring answer Bill.   ^6 self-supporting cone  fired to 4 o'clock (optimum outcome was 5 o'clock).  The total firing was 14:16. (Digitalfire was 14:20 so the total time was in line and the temps at the ramp changes also correlated).  The only anomaly was the rate of 120 instead of 108 so I was a little concerned that the controller was not working properly, however if I don't get an error code then I'll assume it is within its acceptable speed range. 

 

[Bill Kielb]

42 minutes ago, Marilyn T said:

if I don't get an error code then I'll assume it is within its acceptable speed range.

I would agree. Most often when elements run out of power you will see it in a very significant deviation of the final rate, significant extension of the final segment timing ………. followed by the errors. You will know in advance before this happens with your level of observation for normal element wear.

Edited April 27 by Bill Kielb

[neilestrick]

A 4 minute difference and a very small difference in the cone is incredibly accurate for one of these kilns. No worries whatsoever with those results.