Products > Test Equipment
HP/Keysight 66311B magnetic field leakage
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Hydron:
Make sure you have the voltage set correctly, e.g. 240 for europe rather than 220 (go higher rather than lower). Flux leakage often gets a LOT worse the closer it is to saturation.
Mine does make enough humming noise on the ~245-250V they deliver to me that I'm not surprised you're seeing issues near CRTs.
electronomicon:

--- Quote from: Hydron on November 23, 2023, 11:03:11 pm ---Make sure you have the voltage set correctly, e.g. 240 for europe rather than 220 (go higher rather than lower). Flux leakage often gets a LOT worse the closer it is to saturation.
Mine does make enough humming noise on the ~245-250V they deliver to me that I'm not surprised you're seeing issues near CRTs.

--- End quote ---

Thanks for the suggestion! I just set my 33120A (the upper device in the stackup) from 220 V to 240 V and its effect on the CRT is now barely noticable. I hope with some additional shielding on the 34401A’s transformer it will be little enough to easily ignore it.
electronomicon:
So I ordered some mu-metal sheet and applied it today. For each of my two noisy devices one layer directly over the lower side of the transformer and one on the housing beneath (see attached images).
It definitely helps. With just the device closer to the scope turned on it’s just about noticeable, with only the farther one turned on not at all (when I previously had the shielding only applied to the closer one, the farther one made more noise than the closer one). Interestingly, when I turn both on, the noise is most noticeable (the farther one here seems to increase the field, despite not having an effect when run on its own). But even then it’s still acceptable and probably less than only the farther one before.

Maybe it would help to also add a piece of mu-metal to the top of the scope housing? But honestly, with the cost of this stuff I guess I’m happy with it right now (I was lucky and got a piece from an ebay auction comparatively cheap).

Edit: But if you attempt to do something like this, too, be careful with the edges. I cut my sheet with a paper cutter, that worked out great, but it left an edge sharp enough to cut myself in the finger |O.
Gulftown:
Okay that sounds pretty good.
I just ordered some mu metal as well.

I was thinking about reducing the input voltage with 2 20V 600W zener diodes on either side of the transformer inputs. That should limit the input voltage, but introduce some side effects due to the dead time and non sinusoidal waveform in the middle.
Do you think this would work?
Or would it do more harm then good?

 
Gulftown:
Okay I found a solution I think.
I will use a 230V/24V transformer and use it as an bucking transformer to reduce the input voltage on the primary of the original transformer.
That should work without introducing side effects.
I will keep you updated.
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