Magnetic shielding for wire

[emsensors]

Hi,

Does anyone have any experience using the magnetic shielded wire products from Magnetic Shield Corp? Here is a link to their website....

https://www.magnetic-shield.com/index.html

Can anyone comment on the effectiveness (or lack thereof) of these products at audio frequencies? It all looks good on paper but what concerns me is why don't the big wire manufacturers sell similar products? Is there some caveat that I'm not seeing? Thanks!

 

[D.A.(Tony)Stewart]

They help a lot. But have you tried a big CM choke around cable and use balanced paths, minimal loop area and orthogonal routing to interference?

 

[emsensors]

Well, I'm trying to reduce coupling between cables that are running adjacent to one another. I am already using twisted pair but still have problems. My drive signal is running adjacent to pickup signals for 70 ft. Pickup signals are very small and I believe my problem is coupling as I am pretty sure the foil shield that I am currently using is not very effective at the lower frequencies.

They help a lot. But have you tried a big CM choke around cable and use balanced paths, minimal loop area?

 

[D.A.(Tony)Stewart]

try CM choke like that used for video cables except high mu.

 

[emsensors]

My signals are not true differential, does that matter? I will order some common mode chokes and try them. Thanks!

try CM choke like that used for video cables except high mu.

 

[FvM]

There will be a certain magnetical coupling of adjacent twisted pairs in the low frequency range. The effects you described in your previous thread (varying signal when moving the cable of your LVDT-like sensor setup may be caused by similar effects. But it may be also caused by more trivial varying cable capacitance, changing the sensor load.

Before applying arbitrary changes, e.g. using common mode chokes or different cable, I would try to verify possible crosstalk pathes by specific measurements. If it's actually crosstalk, using separate Rx and Tx cables may be a simple solution, however.

My signals are not true differential, does that matter?

Likely. What's against using a truely differential driver and differential sense amplifiers?

 

[emsensors]

Thanks. My sensor end of the cable is passive, so, other than adding a circuit at the remote location (which is not totally out of the question), I have no way of creating true differential signals. If it is changing cable capacitance as you suggest, then what would the solution be?

There will be a certain magnetical coupling of adjacent twisted pairs in the low frequency range. The effects you described in your previous thread (varying signal when moving the cable of your LVDT-like sensor setup may be caused by similar effects. But it may be also caused by more trivial varying cable capacitance, changing the sensor load.

Before applying arbitrary changes, e.g. using common mode chokes or different cable, I would try to verify possible crosstalk pathes by specific measurements. If it's actually crosstalk, using separate Rx and Tx cables may be a simple solution, however.

Likely. What's against using a truely differential driver and differential sense amplifiers?

 

[D.A.(Tony)Stewart]

Since you have not (yet) detailed signal and noise characteristics(V, Z, I, f ) I can add that combined SNR is the ratio of signal to noise current is ratio of voltage / impedance ratio . If sensor is high impedance then lowering it with a FET buffer will help suppress E-field high Impedance, if noise is magnetic and sensor Impedance is Low, measure noise level with a shorted sensor and reduce coupling to imbalanced line by separation, twist cables of noise source, add CM choke to source and/or load or shield source and/or load.

 

[chuckey]

Yes total absence of anything we can get hold of. If the "noise" (frequency?, amplitude?, drive X-talk?) is fairly constant, try using a "hum bucker" . That is feed, a bit bit of anti phase "noise" into your signal circuits to balance or reduce the nuisance effect.
Frank

 

[crutschow]

My sensor end of the cable is passive, so, other than adding a circuit at the remote location (which is not totally out of the question), I have no way of creating true differential signals.

Can you float the sensor from ground and use a differential receiver? That would create a true differential signal.