EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: VoidsWarranties on October 28, 2016, 07:08:37 pm
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My oscilloscope does not pick up much of a 60Hz hum or noise instead it is 55.5khz. I do not know if I should treat this as a good thing or a bad thing, could this mean there is a problem with the scope?
If it helps I do live quite close to a cell tower there are also some photos of the waves below.
(http://uploads.tapatalk-cdn.com/20161028/a4a8a35fccaaad9b78546062b2988b2a.jpg)(http://uploads.tapatalk-cdn.com/20161028/58659002b4ae5e1850f2f5e775a5217d.jpg)
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Did you touch the probe with your finger?
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why do your screenshots confuse me? Does it look like a hint of 60hz hum in the first?
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I did try touching the probe. I should be asking what 55khz is from
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One would certainly expect to see a pretty massive 60Hz hum if you touch the probe tip with a finger (ground clip not connected to anything.)
Please set your scope up as shown in the screenshot below and post the image. Note that both the switch on the Probe, and the channel setting, are set to 10x, and the channel V/div is set to 10V/div and the input coupling is set to DC. Probe ground clip not connected to anything, touch tip of probe with finger. Horizontal timebase at 5 ms/div. (Your amplitude will probably be different but you should still see a clear mains hum.)
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I followed all of you steps and I can clearly see the 60Hz but is nowhere near a sine wave (http://uploads.tapatalk-cdn.com/20161029/8bba016d68128012fdf8e35c36d4cf09.jpg)
Sorry it is not a screen shot from the scope itself, it is just a picture of the screen.
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https://www.youtube.com/watch?v=BFLZm4LbzQU (https://www.youtube.com/watch?v=BFLZm4LbzQU) perhaps? Seems like you have some source of EMI other than mains.
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The 55 kHz is from the fluorescent lights. If you make your measurements in the dark that should go away.
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I followed all of you steps and I can clearly see the 60Hz but is nowhere near a sine wave
(image snipped)
Sorry it is not a screen shot from the scope itself, it is just a picture of the screen.
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I have CFLs, mains LED bulbs, UPS and other SMPS, wifi routers, cellphones etc. operating all around me and I still get a pretty clean mains hum as my screenshot above shows.
Does it do this on all channels or just CH1? Does it do this with just the one probe, or do you see it with every probe and on every channel?
Is your scope's mains power cord plugged into a UPS, or do you have a UPS or other heavy SMPS connected on the same mains circuit as your scope? Just grasping at straws here. It sure looks like you are picking up some heavy HF EMI as well as a very distorted 60Hz mains supply hum.
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I have checked all of the channels and probes but they are the same as channel one. I do not have anything that should change the wave that much. When I did my tests I only had a security camera dvr and my cfl bench lights, no inverter-type devices any where on any circuit.
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I just tested it with the lights off and I got a much better 60Hz sine wave. I did not expect them to make such a large difference
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