Is there any one can help me on how to calibrate a benchtype laboratory ovens and incubators?

Is there any one can help me on how to calibrate a benchtype laboratory ovens and incubators?

Welcome,

I think your question lack details for others to provide you with a good or appropriate answer. For a start, you may want to have a look at these two threads for an idea.

Oven Calibration Range: How many points? (http://elsmar.com/Forums/showthread.php?t=11609&highlight=calibration+oven)

Setting Calibration Tolerance on Gauges - Oven Calibration and Stepped Plug Gage (http://elsmar.com/Forums/showthread.php?t=17746&highlight=calibration+oven)

Hello there!:bigwave:

Calibration of a bench-top oven can range from a simple one-point check, to a full-blown uniformity survey.

In general, you will want to check the oven across the range of use. So, say the range of use is 60-100C. I would check the oven at 60, 80, and 100 C. I would place a certified thermocouple/ thermometer within two inches of the controlling thermocouple, and verify the accuracy of the the temperature controller. If it is feasible, you can remove the control sensor, and place in a furnace/ oil bath/ etc.

If there is a timer on the oven, I would verify the timer. I would follow the threads on verifying timers/ stopwatches, but in short, get a certified stopwatch, and start it when the timer stops.

NOTE: This is a simple calibration of the temperature controller.:) Uniformity profile of the oven is a different matter. Also, one may want to perform a performance check of the oven, which would involve placing a standard probe in the working zone of the oven, and verifying its accuracy with the temperature controller. ;):D

That was quite rudimentary. Let me know if you need more involved information.

BTW, we appreciate you dropping by the Cove. Please let your work associates know they are welcome to drop by also.:)

Is there any one can help me on how to calibrate a benchtype laboratory ovens and incubators?
Calibrate your temperature controller first. Then map the temperature of the oven by selecting appropriate zones based on your oven compartments and use and validate the oven. Consider challenge areas in the oven to ensure that the complete oven volume is good for your use. Ensure that a qualification of the installation is performed to check for any leakages and proper functioning of other parts before temperature mapping.

Sorry that I haven't been able to post much lately. I am at my new job back in Texas and very busy.

A quick note about incubator type ovens: In my brief time in the pharmaceutical world (the last three years) we had to do some incubators that had pressure sealed doors to the chambers. This was a difficulty in verifying chamber temperature, as it would not reach temperature without a good door seal. When you attempt inserting a typical thermocouple, it was just large enough that it interrupted the door seal, and made readings difficult.

We overcame this by using a very small gauge thermocouple and slipping it behind the door gasket (if you're trying to calibrate that type incubator, it will become self-evident). We slipped the very thin thermocouple behind the door gasket as close as possible to the latch assembly to minimize the impact on the door seal.

We overcame this by using a very small gauge thermocouple and slipping it behind the door gasket (if you're trying to calibrate that type incubator, it will become self-evident). We slipped the very thin thermocouple behind the door gasket as close as possible to the latch assembly to minimize the impact on the door seal.
Jerry makes an excellent point - access can often disrupt the very process you are trying to monitor. If you struggle to get access to the oven via a door seal you may want to consider fitting a suitable chamber gland to give access to your thermocouples. A wide range are available and many decent engineering firms can fit them without damaging the integrity of the oven itself (usually in the door to avoid electronics and moving parts).

:2cents: My two cents on the calibration of the thermocouples: I recommend using loop calibration. Calibrate the T/C's before the study to show they are accurate and linear, and then after the study to show they remained accurate and linear throughout. Always calibrate more T/C's than you need, that way you do not have to abandon the study because you pinched a wire in the set-up.

One other thing - be very careful defining your acceptable temperature spread - base it on what your process actually requires, rather than the often misleading information in the oven manufacturer's sales brochure. If +/- 1.0 degree will do, don't be lured by +/- 0.1 degree literature claims (I've been there, got burned and won't get fooled again!)

Jimmy

Good stuff, Jimmy. As always, excellent stuff from Jerry.

Pressure (and vacuum) for that matter, get very difficult when calibrating. That's why one is always grateful for a port on an oven. Compression fittings can be used in the event of pressure/vacuum. If just a regular forced-air oven, the port can be used to place a calibration probe next to the control probe. Although, like somashekar noted, I like calibrating the controller first, preferably removing the sensor probe and placing in a calibration environment.

One issue that has popped up is placing an offset on the oven. Generally, you will want to calibrate the controller and make it accurate. Then, given the temperature unformity/ profile survey, an offset may be entered in the controller for low/high temperature conditions. So, say your oven runs a bit cool compared to the controller, you may want to add 2-3 degrees of offset to bring the temperature up. IMPORTANT: If you enter an offset in the controller, clearly mark it on the calibration document. Otherwise, the technician will spend 1/2 day trying to get the 3 degrees of error out of it!:notme::D

If the technician will enter it manually (for 380 F run, set controller to 383 F), clearly mark on the outside of the oven. Auditors get persnickety about controllers being different than the process parameters; having it clearly marked keeps the confusion down. It's best to enter the offset in the controller. Most all digital controllers have "offset" features these days. Again, just make note if you make an entry.

:topic:

If you ever get to be part of the process of buying an oven, please match the equipment with your requirements. Do you have a uniformity requirement, and what is that uniformity? How large is your batch? Will there be constant opening/closing? Will you be adjusting the temperature a lot, and how long will you have before it needs to be stabilized? Do you need an independent high limit? What about a recorder, and how many points need to be recorded? What about a timer? If you have a timer, do you want 2 timers, one for heat and one for the entire oven?

Like every other piece of equipment, ovens are engineered and designed for general/specific purposes, and obviously range from inexpensive to costly. But, the equipment should match the needs. So, always make sure you account for all the process requirements prior to purchasing.:agree1: