Author Topic: Connecting test equipment into a filtered/conditioned power board?  (Read 565 times)

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Offline seon

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Hi folks,

I'd love to hear everyones thoughts on if it's worth buying a good filtered/power conditioned power board or even a UPS to connect my Siglent Oscilloscope into? Would it help reduce mains noise at all?

My work space is full of all sorts of noise - computers, other tools & hardware, wifi, lights etc... it's not like I'm in a professional work area, or working in a faraday cage, so I know there is not a lot I can do about general ambient noise pickup on the scope, but I figured that maybe a power conditioned power source might help, or am I just going to waste my $ on something that I really can't measure the results from anyway?

Does anyone use one and recommend the results?

Maybe folks have other general suggestions on "reducing noise" in the workspace to help reduce ambient noise the scope picks up?


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Offline Rerouter

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Re: Connecting test equipment into a filtered/conditioned power board?
« Reply #1 on: December 13, 2019, 11:43:26 pm »
If you keep the ground lead on the scope probe short, there should be very minimal mains noise, If its a meter long or not used at all, it will appear,

Offline DaJMasta

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Re: Connecting test equipment into a filtered/conditioned power board?
« Reply #2 on: December 13, 2019, 11:50:23 pm »
Don't bother.

Test equipment who's readings can be effected by conducted EMI have good EMI filters on their mains input and power supplies with appropriate filtering.  To be able to meet their spec they have to be able to be largely environment-independent, so if they're susceptible to it, appropriate measures are taken.

Other than that, make sure you're using shielded cables, shielded boxes, or even guarded cables if you're dealing with something where ambient EMI could be a problem.  You can probably see that the scope without a probe has about the same input noise as with it attached  because the probe uses coax to shield the signal line.  If you see substantial noise in both, maybe mains filtering would offer some improvement, but I doubt this will be the case.

Offline GreyWoolfe

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Re: Connecting test equipment into a filtered/conditioned power board?
« Reply #3 on: December 14, 2019, 02:32:19 pm »
I have a UPS on my workbench, mostly for power fluctuations as it has automatic voltage regulation.  I don't know how good the filtering is.  It also lets me power a bunch of stuff and only use 1 wall outlet so there are advantages to using one.
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Offline Performa01

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Re: Connecting test equipment into a filtered/conditioned power board?
« Reply #4 on: December 14, 2019, 04:38:37 pm »
I don't think that a filtered power supply will change anything. The filtering will be effective for low frequencies, where the DSO has plenty filtering itself, whereas the power cord will still act as an antenna for high frequency radiated signals. The latter are much more likely to enter the DSO via the DUT and probes anyway.

A good test can be set up with the DSO itself:

Look at the screenshot below and copy the settings:
Inputs: left open (nothing connected)
Trigger: mains
Vertical gain: 500µV/div, 20MHz bandwidth limit
Timebase: 50ms/div
Math: FFT, 10 times averaging, Flattop window, 1Mpts, reference level -60dBV, Scale 10dB/div - as can be seen in the screenshot.

[attachimg=1 width=800]

The search conditions for the peak table were set to -120dBV (1µV) threshold and 10dB Excursion.
As can be seen, the strongest spur up to 1MHz is not near the mains frequency, but at 1MHz at -107dBV, which is less than 5µV RMS.

If your test shows no spurs stronger than, say, -80dBV in that frequency range, then the internal noise (including the one coming from the power supply) would certainly not be significant for your measurements.

« Last Edit: December 14, 2019, 04:41:32 pm by Performa01 »

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