Hi Cortland! Let me sprinkle in a few comments as we go along. First, my description was a suggestion to keep him going when his computer died. But with today's goodies, that certainly isn't the path of choice!
I tried to get him to do a stand-alone Peak plot, which would have shown him his worst case frequencies. Then, he could revisit each high peak, without sweeping, using the external QP adapter to accurately measure the amplitude. (That way, he wouldn't have to worry about sweep speeds.) > Ed, > > As one who has done all that manually, I can second your comments. But it's > important not to bypass the QP adaptor. > > The QP adaptor ALSO provides correct bandwidth (200 Hz, 9 KHz, 120 KHz) and > detector time constants for each frequency range. This means that the > adaptor has to be used during all record testing BUT the QP detector > function is only selected when a QP reading must be taken. This next item is really interesting: > One common error made by folks unaccustomed to doing manual readings is > leaving the analyzer in logarithmic mode for QP or average measurements. > It's important to first switch to linear mode before doing a QP or video > averaging reading. > > The analyzer might switch units (uV or volts) instead of DB when you go to > linear mode; this can be overcome by selecting dBuV _after_ switching to > linear mode. Are you saying that the averaging process, handled by the SA firmware, averages by display units, and not by the absolute levels represented by the display? For instance, point #1 is displayed at 40dBuV and point #2 is displayed at 80dBuV, so the average (the wrong way, if you are using a logarithmic display) is displayed as 60dBuV? The firmware does not know that 40dBuV is 100uV and that 80dBuV is 10,000uV, and that the average of 100 and 10,000 is 5,050uV, or 74dBuV? Oh no!? > When using the QP detector, a 100 KHz sweep might take a couple of minutes > above 30 MHz. You can imagine how long it would take below! For this > reason, a practical QP sweep will examine only the peaks close to the limit > or above. But if you are observing the output of a QP detector, you already have to be sweeping very slowly. You don't know when you will encounter a peak until you actually hit it. It seems to me that you really should use a Peak detector, sweeping fast, and then let a computer or operator decide to go back and remeasure, either at a certain peak, or over a small frequency span around a peak, using the CISPR BW and QP detector. > Finally, I can say that doing ALL testing in manual mode, as at a former > employer we did, that you will end up replacing some of the switches on the > analyzer annually, maybe more often. A skilled technician can actually > compete with computer control in taking readings, but he hits those buttons > several times per second when he's doing so, and the force of rapid inputs > is just more than they can take. Yes! I had to retire an HP-3325 sig gen, primarily because the tech using it had the strength of a gorilla and a strong preference for positive tactile data inputs! Actually, it's a waste of a human to stick someone in that kind of a situation. After a few thousand :-( button pushes, the average human has begun to glaze over and go into robot mode. This mode is then usually terminated with the utterance of "Oh no!". Regardies, Ed -------------------------- Ed Price [email protected] Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: [email protected] Date: 09/28/1998 Time: 11:57:29 -------------------------- --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
