Bob, Our calibration software monitors the linearity of the amp while performing the Constant Field Strength method calibration test. A 1db change in the amp's input will result in a 1db change in the amp's output (or fairly close to it) if operating within its linear range. If the test software determines the amp is operating outside its linear range or has reached the maximum input power without achieving the target output, a value of "99" is stored for that point and frequency. When the data is calculated according to the procedure in D.4.1 this point will automatically get thrown out at that frequency. If five points or more fail the criteria, then we are not uniform at that frequency at our desired power level which can be documented in the test report. If a lot of frequencies fail the criteria then the target power level can be reduced or the Uniform grid size can be reduced.
The linearity check described in section 6.2.1, only takes a couple minutes to perform on the final data determined by the procedure in D.4.1. Using the Constant Power Method and selecting a power level that will not saturate your amp and generate data that will not fall below the noise floor of your probe is fine for determining Uniformity, but then you have to calculate the power needed to generate 18V/m at 12 of 16 points and then run the linearity check to make sure you are not in saturation. If done properly, both methods should determine the exact same result. If you don't have enough power to do the Constant Field Strength method then you won't have enough power to do the test at the target power level. The field uniformity is the same regardless of what method you use to determine it as long as you perform the test within the constraints of your equipment. The Other Brian From: [email protected] [mailto:[email protected]] On Behalf Of Bob Richards Sent: Wednesday, February 01, 2012 1:46 PM To: [email protected] Subject: RE: IEC 61000-4-3 Field Uniformity Measurement Brian, According to the standard, there is a linearity check that must be performed to insure the amp is not in saturation. This check must be performed regardless of which method is used. Granted, you will know at the end of the constant-field method that you might have a power problem, without having to run the linearity check, but it still needs to be done so you don't really save time. I've tried the constant field method before where one of the outlying points was in a null and the amp did not have enough power to pull it up to 18v/m. The only way I could complete the calibration was to use the constand power method, so at least in this scenario I had wasted time with the constant-field method. I wish I had a better chamber and bigger amp, but management just would not buy them for me. :-) Bob R. --- On Wed, 2/1/12, Kunde, Brian <[email protected]> wrote: From: Kunde, Brian <[email protected]> Subject: RE: IEC 61000-4-3 Field Uniformity Measurement To: "EMC-PSTC" <[email protected]> Date: Wednesday, February 1, 2012, 10:38 AM Do you only want to determine Field Uniformity or do you also want to determine the power you need for testing? If you use the constant power method, it works good to determine uniformity but I feel the data collected is not the best for determining test power. Using the Constant Field Strength method and storing all the data, you can determine field uniformity and better determine your test power in one test which can save time. The only thing is you have to know you have a good setup and enough power to perform the test with your amps operating well within their linear range (no clipping). The Other Brian -----Original Message----- From: [email protected]<http://us.mc1616.mail.yahoo.com/mc/[email protected]> [mailto:[email protected]<http://us.mc1616.mail.yahoo.com/mc/[email protected]>] On Behalf Of WNya Sent: Wednesday, February 01, 2012 4:36 AM To: EMC-PSTC Subject: IEC 61000-4-3 Field Uniformity Measurement Dear Experts, Two methods are mentioned in the standard - constant power calibration and constant field strength calibration. Is there a preferred method (benefits?) of one over the other? If yes, why? What would be the considerations to use constant field strength instead of constant power? Is it related to the equipment setup? Our system integrator recommended constant power method because he is, as he claimed, more familiar with it. Although both achieved the same purpose, what are the engineering differences between them? 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