i want to ask one question please,i need to measure the temperature of the material to be dried in the microwave oven just online while drying so as i can log my data and see how the temperature profile is behaving,so can any one please suggest the sensor type that can be used inside ?

 

A tube filled with gas or liquid with a pressure sensor outside the oven.

 

You do not mention a temperature range. The majority of temperature sensing probes I have see for use in a microwave oven have all been thermistor probes designed specifically for use in a microwave chamber. Most have a range not exceeding 199 degrees F. Here is an example of a typical GE Microwave Oven Probe. It also seems the fad for probes in a microwave oven has passed as I seldom see them offered on new models. The idea being you do not want a probe which will react too much with the microwaves. Just about any data logger should work for recording the temperature. I would try a probe like the linked probe or similar thermistor probe and then calibrate your system.

I also like Albert's suggestion.

Ron

 

hi
thank you for the recommendation ,but wouldn't this be measuring just the temperature of the whole microwave cavity rather than the material to be dried ?what i need to do is just paper drying experiment .so i was just quite extensively searching what sensor can measure the temperature of the paper it self online while drying .

 

Any heat in the chamber is a result of the "load" in the chamber emitting heat. Other than whatever is absorbing microwave energy the chamber is cool. Normally a probe is inserted into the "load" be it a pork chop, cup of coffee or a cup of water. I am not sure how to measure the surface temperature of a sheet of paper in a microwave. A stack of paper maybe by inserting a probe but a sheet or two I don't know. Not sure how well even an IR detector would work from outside the chamber. Interesting challenge.

Ron

 

Hi Ron,yeah you right and it is a bit of challenging actually,but i like the IR detection option you suggested ,it may be is possible .actually for experiment purpose i will be using it on just a stationary paper sheet ,but in the real production line the paper sheet is movable .i will search for IR detection sensors may be, and thank you for the suggestion .
Mitku

 

A Google of "IR temperature sensing in a microwave" yielded some interesting results. My neighbor and I were heating my new garage floor last night to apply sealer to concrete using "torpedo" kerosene heaters. I was using a little hand held IR sensor to get the concrete floor temperatures. Hoping it warms up a little today. About 35 F outside so far and we have the heaters going again. Hope to get a second application done. This project should have been done by August! Getting cold about now in NE Ohio, USA.

Ron

 

hi
thank you for the recommendation ,but wouldn't this be measuring just the temperature of the whole microwave cavity rather than the material to be dried ?what i need to do is just paper drying experiment .so i was just quite extensively searching what sensor can measure the temperature of the paper it self online while drying .

You can't just put any old probe in the microwave - I tend to place my trust in the one supplied with it by the manufacturer. The most common type I've seen is the stainless steel spike you stick in the turkey to make sure its cooked in the middle.

Microwaves go in a straight line and reflect like off a mirror (that's why they use microwaves for radar) they bounce around the compartment in a set pattern and create nodes that sum or cancel - the manufacturers usually install paddle vanes that rotate and randomise the fixed reflection pattern - but hot spots still seem to be unavoidable.

The only thing I can think of that stands a chance is; a pyrometer thermometer, The sensor certainly wouldn't survive inside the oven compartment - the clever bit is cutting a hole for it to peer through without creating a slot resonator.

 

How about infrared thermometry? There of course is the drawback, namely temperature color factor aka blackness factor but if once calibrated it shows quite accurate. Only the problem, You must drill the small millimeter size hole in the cooker wall that IR ray may see through. As known, the glass is 100% stopper for IR. Hole must be tiny enough to stop the MW energy leaking out, but wide enough that ray diameter.

 

How about infrared thermometry? There of course is the drawback, namely temperature color factor aka blackness factor but if once calibrated it shows quite accurate. Only the problem, You must drill the small millimeter size hole in the cooker wall that IR ray may see through. As known, the glass is 100% stopper for IR. Hole must be tiny enough to stop the MW energy leaking out, but wide enough that ray diameter.

Its not easy to peel that apart from what I just said.

 

RE: IanField ""Microwaves (..) bounce around the compartment (..) in and out""

No-one is cancelled the lambda quarter principle. If somethin is smaller than quarter, it may go through exclusively in the state of resonance, but if it is smaller than lambda tenth it cannot soak through even at resonance.
If 2400 MHz has lambda 300/2400=12,5 cm, then lambda quarter is 31 mm and one lambda tenth is 12 mm.

Okay, You may dispute, but what is about harmonics transport. Well, I have no much data about distortion proportional weight factor into cooker spectra, but over the 5th I bet there ought be nothing. Therefore 2 mm ought be considered as practically safe gap (I mean the largest size of hole) and 1 mm may be considered as absolutely safe. More, with what You risk in case of I was mistaking? With price of 2.31 USD costy device of one-point reading? Is it so painful?
www.ebay.com/itm/Mini-Digital-Non-Contact-IR-Infrared-LCD-Thermometer-DT-300-Black-UD6-OS/162318892895?hash=item25caf5bf5f:m:mkdqpCZjMpqZNB6XKcGFPbg