Instrumentation Special: Tribo Electricity and Micro Phonic Noises

Do you use a standard length of cable in your tests?

Yes. Cable length tried are 1m long. However Micro phonics were generated by tapping, jerking or shaking the cable to see how bad these signals could be.

It will be much better to use some standard force and motion or vibration and that part is yet to be taken up.

Basically motion of conduction rubbing the insulator generates these micro phonics charge impulses. While charge is generated in insulator media, conductor transmits the charge as signal.

Tribo electricity can cause high voltage spark in crystals on surface when heated. This I have seen when I was working on thermoluminescent material. PVT, Polyethylene and PTFE all these used as cable insulators also generate similar charge when cable is moved and surface area changes.

Shyam,

can you discriminate between triboelectric (conductor-insulator rubbing) and thermoelectric (conductor-conductor) voltages?

The frequencies in your plot - estimated between 200 and 1000 Hz - seem to be too high for tribo (your movements should be dominant) and seem to be too low for thermo-electricity. I would like to see the result if you use only 100KOhm and tune up the amplifier's sensitivity a factor of 100.

I would suspect a highly nonlinear "generator" by stick-slip movements inside the cable. Try to fill with oil and the result will be dramatically improved. Krytox for example (if silicone is allowed).

The voltages indicate tribo as thermoelectric voltages should be much lower.

What about filtering by cable capacitance?

Your 10M resistor together with a cable capacitance of 100pF/m will act as a low pass filter near 1.5KHz bandwidth.

What does the amplifier input add to this?

The best cable I tried did not have the shield with braided silver-coated copper wire but only one bare wire lengthwise and around a sheath of conducting plastic lubricated to minimise tribo-noise.

Conducting plastic is not conducting nearly as good as copper so the lengthwise wire is needed.

I never saw a difference between connector types.

RHABE

It is not a thermoelectric signal. Thermocouple formation hardly generates 40uV/C potential in Type-K thermocouple. In this case, signal is in the form of charge and loaded on cable capacitor and charge bleeds through discharge resistor which finally shows above voltage characteristics.

If discharge resistance is decreased then peak voltage comes come down and damping is faster.

I also injected charge into amplifier having low impedance and then similar response was observed as one will see in charge amplifier.

Some insulators create high voltage spark like noise.

Thanks to the three of you.

This post is old and yet relavent.

I am looking for manufacturers of PTFE coaxial cables with semiconductor layer for copper braided shield single Co-axial or double as tri-axial cables. Only inner insulation of Teflon/PTFE required.

I want to hear from all friends.