Hi, There are messages on this server about DVM not being acceptable for measuring leak currents. There is also comments about aliasing problem found in some DVMs.
As a designer of digital voltmeters, the sampling rate of the analog to digital converter in DVMs was set to a multiple period of the power line frequency for rejection of that power line signal in small signal measurement environment -- 60 to 120 dB. This technique is a type of 'notch filter' that rejects the fundamental frequency and all of its harmonics. The amount of rejections, attenuation, of the fundamental frequency and its harmonics is related to how close the sampling time matches the period of the frequency of concern and the phase noise of the sample time and of the frequency of concern. In many of the slower sampling DVM the sampling time was fixed for rejection of both 50 and 60 Hertz. It is not aliasing of signals! This method is probably still used for very inexpensive DVMs, but will not be used as such in the more accurate and expensive DVMs. The specifications should tell you what to expect. I think the DVM type of measurement design is the reason for the safety groups concern when the measurement is done. It is not an aliasing problem were new signals are produced. Francis Helix Technology Incorporated Granville-Phillips Division Boulder, CO 80303-1392 303-998-4092 ffied...@granville.com http://www.granville.com --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
