Oven temperature control

[Bruce Platt]

Recently purchased a new Bosch range, wife was having trouble cooking with it, called the repairman who said it was working correctly. I brought home some temp measurement meters from the office to check it out.

When set at 400, the oven cycles from 367 to 425. This seems excessive to me, anbody know how close oven controls should be.


TIA

[leehljp]

It seems excessive to me too, especially for a Bosch. I don't what a company would say is excessive. I would go to their web site and email them. Ask if their models should do better than that. If they say it should, then tell them you have one that does not and the repairman said it was OK.

[bigfoot]

When you tested the temp, did you check temp at or near the oven sensor (thermocouple?)

That is about a +-7% variation, which does seem excessive for an oven. I would think no more than 2% would be the spec. I agree, contact the manufacturer with the data you have collected.

[jziegler]

Sounds excessive to me as well. I'd expect a +/- 5 10 degree varaiation. Which is around 2%. It's not like temperature control is rocket science....

Jim

[bigsteel15]

When I did repairs we always looked to have a swing of +/- 10 degrees when set at 350F.
That was in the days of old manual controls. I assume you have electronic.
You didn't state if this is electric or gas oven. May also make a difference.

[LCHIEN]

Engineering wise, saying a temperature is a so-many-percent variation or swing is totally inaccurate because F and C temperatures are based on an arbitrary zero!

I think the means of measurement is very imortant.
What were you measuring when you made these measurements. If you measured the heating elements then the swing would be much, much greater. If you measured the inside of a cake then the temperature swing would be much smaller as the thermal mass of the cake averaged out the temperature swing. If you measured the air then the measurement would depend upon how close you got to the elements vs the object being cooked. If you infrared-measured the walls of the oven you might get what you measured. You'd probably get the most accurate and useful measurement inside any food item.

Assuming you measured closer to the elements then the swing might not be abnormal. I think the most important thing you should compare to others is how frequently the oven cycles on and off. When its at temperature, I would think it would cycle on and off maybe once per minute to once every few minutes.

The difference between upper and lower points are called hysteresis, the temperature control is called "bang-bang" in engineering slang and just involves full on and off switching. If you have small hysteresis then the controller works too often with some disadvantages.

[Bruce Platt]

Well. the local dealer decided he didn't want to deal with me anymore, because I obviously was better equiped to judge the performance of the oven than his repairman. Not that I am upset, he is completly refunding my purchase price.

It is an electric oven with electronic controls. It has a simple on/off controller but the deadband is huge. PID controllers are so cheap I am surprised that a range costing over $1500 does not include one.

But BORG saves the day. They recommended the GE "true temp" system, and agreed to let me test it in the store. All testing was done with an empty oven (admittedly worst case), with the thermocouple in the air in the center of the oven. GE controlled at 400 with in +/- 5 degrees F.

Now SHMBO is happy, time for a new power tool.