[Histonet] Re: Microwave procedure for monitoring temperature

wlove <@t> att.net wlove <@t> att.net
Thu Jan 18 13:17:24 CST 2007

Hello, we are a company that designs, deveolps and produces laboratory and industrial microwaves.  Between my partner and myself, we have over 50 years experience in microwave equipment used in heating materials, like laboratory microwaves (commonly called ISM equipment).  The issue of microwave leakage, their acceptable levels and how/who to measure them has been problematic for the last 20 years or so.  Different limits apply to different countries and in some cases individual states in the US.  Who tests for the leakage is less important than the type of meter used and under what conditions the test where performed.  

First be sure to use a microwave leakage meter designed to read microwave fields at 2.45 GHz.  Furthermore, the meter should be calibrated and traceable to NIST (US National Institute of Standards and Technology).  All of the small cheap meters not calibrated and tracable to NIST we evaluated have given both false positive and negative readings compared to those that are calibrated and tracable to NIST.  No matter if the meter operator is trained or certified, if he/she is using an uncalibrated or without tracability to NIST, any readings taken are likely faulty.

Next, the load in the microwave should be small as large loads adsorb microwave energy and therefore prevent the microwave energy from leaking from the microwave, hence another potential source of error.

Microwave leakage is statistical, meaning just do not do one test and assume everything is OK.  Microwave leakage can vary with time (due to the turntable or mode stirrer position, load and the phase of the line cycle at the time of measurement at that instant.).  So the test should be repeated more than once for more valid testing.

I believe CLSI GP-28A, the standard for using a microwave in the laboratory was written by a number of people working to develop a guideline.  As a member of IMPI, International Microwave Power Institute and former board member and section president, to the best of my knowledge the group that developed GP-28A did not contact IMPI for guidance, nor have I heard of anyone whom I consider to be in the ISM community to be contacted.  I was able to unofficially read a draft as one of the members was looking for feedback, but this was well after they approved the draft.

I agree with Phil McArdle of EB Sciences that much of GP-28A is very good and useful, but there are some serious issues that should be corrected.  In the meantime, only calibrated and traceable to NIST leakage meters should be used multiple times to measure leakage.

Best regards 

Wayne Love 
Microwave Research and 
Applications, Inc. 
8673 Cherry Lane 
Laurel, MD 20707 
Phone 301-953-1771 
Fax 301-369-0523 
WebSite www.microwaveresearch.com 
Email info <@t> microwaveresearch.com 
Cell 630-269-5158 
Direct email: wlove <@t> att.net

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