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2306 spurious radiated noise

2302, 2303, 2303-PJ, 2304, 2306, 2306-PJ, 2306-VS, 2308
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IvorBowden
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Joined: May 1st, 2013, 6:44 pm
Country: United States

2306 spurious radiated noise

Post by IvorBowden » July 17th, 2014, 4:25 pm

We have multiple 2306 supplies that exhibit random spurious noise. This is not on their outputs specifically, but gets into the systems, causing false scope triggers and "dirty" waveform captures. The noise is characterized by short bursts of several cycles of HF inside a typical window of around 100 nS. The bursts may be random or repetitive at around 7.6 uS rate. Holding a scope probe near the 2306 front panel may also show it. This noise can get into systems even when the 2306 is not connected, just plugged in and turned on. Removing the mains ground pin from the line cord doesn't help. It varies quite a bit, some days are relatively quiet, others relatively noisy. Sometimes turning the 2306 off and on, or loading the 2306, will change the symptom. How to get rid of this noise?

Dale C
Keithley Applications
Keithley Applications
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Re: 2306 spurious radiated noise

Post by Dale C » July 18th, 2014, 12:18 pm

This sounds like the clock for the micro processor inside the 2300 series supply. I believe it is a 8MHZ to 10MHZ clock.
Although, I would expect this to show up on the output and be radiated like you mention.
Is the case grounded to earth through the power line? Normally that is the case. But it does not sound like that is the case with this one. That is one thing I would check.

IvorBowden
Posts: 6
Joined: May 1st, 2013, 6:44 pm
Country: United States

Re: 2306 spurious radiated noise

Post by IvorBowden » July 21st, 2014, 12:25 pm

Yes, the line cord ground is connected to earth ground along with the rest of our equipment, including scope grounds of course. As per post statement, removing the ground pin doesn't fix the problem. Also the symptom is observed even if the 2306 output is not connected (connector removed, no wires of any kind except the line cord). Apparently the noise is going through the AC mains. Definitely does not look like a processor clock. Typically I see this kind of problem with switch mode power supplies. When it is random / intermittent like this sometimes it is some type of bad connection. I don't want to open / dig into the 2306. I'm considering getting some ferrite core material for the line cord to see if I can block it. While it also radiates, sometimes enough to - up with a floating scope probe a few feet away, that isn't the way it's getting into our systems, it is getting into the grounding.

IvorBowden
Posts: 6
Joined: May 1st, 2013, 6:44 pm
Country: United States

Re: 2306 spurious radiated noise

Post by IvorBowden » July 29th, 2014, 9:35 am

Can we get a copy of 2306 FCC part 15 class B compliance test, please?

Dale C
Keithley Applications
Keithley Applications
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Re: 2306 spurious radiated noise

Post by Dale C » July 31st, 2014, 11:17 am

Strangely FCC part 15 does not apply to test and measurement equipment. If it did we would use class A rather than class B. We have something similar for Europe (CISPR 11) but it is not our policy to release our test reports to the general public. I have attached a copy of our 2306 DoC.
Attachments
2306conformity.pdf
(145.15 KiB) Downloaded 1529 times

IvorBowden
Posts: 6
Joined: May 1st, 2013, 6:44 pm
Country: United States

Re: 2306 spurious radiated noise

Post by IvorBowden » August 7th, 2014, 4:54 pm

Thanks for that information. Strangely, 2306 Specifications Sheet call out Class B compliance:
EMC: 2302, 2306: Conforms with European Union Directive 89/336/EEC, EN 55011, EN
50082-1, EN 61000-3-2 and 61000-3-3, FCC part 15 class B. 2302-PJ, 2306-PJ: Conforms
with European Union Directive 89/336/EEC.
All (or at least most) of our 2306 units radiate enough to - up with an open scope probe at a distance of a few feet.
These are all units that have been in service for a while, I don't have new units to test.
I'll contact our Keithley FAE directly about this, no need to release documents to public.

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