Coaxial or twisted pair?

[GeoAVR]

Which is the best cable for shielding against low frequencies EMI RFI of 50Hz to 100Hz?

The cable has to carry signal with 100kHz BW

Thank you in advance

 

[jiripolivka]

A good coaxial cable and connectors are best to reject ANY EMI/RFI at ANY frequency. If you can, use the semi-rigid cables with SMA connectors. Their sheath is full copper and SMA connectors offer >90 dB leakage rejection.
BE ready that low-frequency stray signals rather enter not by the cables but through other devices linked by the cables.

 

[Audioguru]

A telephone line is balanced and cuts frequencies below 300Hz then its small amount of mains hum is not heard.
Most audio cables are unbalanced so a shielded audio cable should be used.

 

[betwixt]

Co-ax is almost always better but you didn't specify what frequency you are carrying along it and at what impedance. The answer may depend on that.

Brian.

 

[GeoAVR]

Co-ax is almost always better but you didn't specify what frequency you are carrying along it and at what impedance. The answer may depend on that.

Brian.

Thanks Brian,

Is for a capacitive sensor reading with sweeping frequencies from 10 to 100kHz.

What do you mean Impedance? The load is capacitive although a think after increasing the cable length a few meters its has some inductance too. (phase increasing from -90 to -85)

 

[betwixt]

From an interference point of view, the screening effect of the co-ax shield is ideal but it also has other effects. Most dominant is the effect of inductance along the wire length and capacitance between the wire and shield. The diameter of the center wire to the shield inner surface also gives it a characteristic impedance which under some circumstances you need to match with driving and terminating resistances. If you are using good quality RF cable (usually Z=50 Ohm or 75 Ohm) but low frequencies you are probably safe to ignore the impedance although for capacitive sensing you obviously have to take into account the cables own contribution to your readings.

I'm curious to know why you have a capacitive sensor witha frequency sweep.

Brian.

 

[D.A.(Tony)Stewart]

Which is the best cable for shielding against low frequencies EMI RFI of 50Hz to 100Hz?

The cable has to carry signal with 100kHz BW

Thank you in advance

Shielding is a 2 way property fro ingress and egress and the transfer impedance varies widely with quality of cable < 1Ghz

But for 50Hz to 100kHz source and load impedance are critical as well as balance.
Twisted pair, CAT 3 or 5 cable should be adequate but you will most likely need high Mu ferrite balun or CM choke to attenuate common mode noise as done in all telephones and ethernet ports.

Loading effects vary from 30 to 100 pF per meter must be factored with high impedance endpoints.

 

[FvM]

Best solution in terms of interference supression is shielded twisted pair and for single-ended circuits triaxial cable.

 

[GeoAVR]

From an interference point of view, the screening effect of the co-ax shield is ideal but it also has other effects. Most dominant is the effect of inductance along the wire length and capacitance between the wire and shield. The diameter of the center wire to the shield inner surface also gives it a characteristic impedance which under some circumstances you need to match with driving and terminating resistances. If you are using good quality RF cable (usually Z=50 Ohm or 75 Ohm) but low frequencies you are probably safe to ignore the impedance although for capacitive sensing you obviously have to take into account the cables own contribution to your readings.

I'm curious to know why you have a capacitive sensor witha frequency sweep.

Brian.

There are some applications that the liquid properties you want to measure, also change with frequency.