Dear researchers,
I have a rotating wheel in ABS, separated by a PTFE disk from it's housing (made too of ABS). The wheel has about 300mm^2 of contact with the PTFE disk, as does the PTFE disk with the housing.
Both ABS and the PTFE are excellent insulator of course.
In this system a few delicate components are placed near (0.2-0.8mm) the flat face of the rotating wheel.
What method would you suggest to reduce the risk of ESD damage to the components?
Best Regards,
Davide Bortolami
One possibility is to use ABS types with an increased electric conductivity in order to discharge your disc in a controlled and continuous way. The save way the current can take (grounding) should be short and have a decent conductivity. Especially for the PTFE you might want to check if you can improve it somehow (more wires, flatter PTFE-disc, etc.) as you will not find a huge variaty of PTFE types with an improved conductivity.
Electrostatic charge occurs by friction (triboelectricity) between materials with different dielectric constants (between PTFE and ABS it is such a difference).
You can use the same material for both pieces (if mechanically possible) or you can use an antistatic spray or a graphite grease. It is important to avoid an electrostatic discharge.
I am not sure what you are investigating here, but if it is triboelectricity then you don't want methods to eliminate it! Do your sensitive components need to be connected or affected by the plastic disks? If not. cover them with insulating lazquer and then a very thin metal shield which you connect to earth - or the 0 volt line for the circuits. If they do have to make some form of contact with the disks e.g. to measure surface charge states, then it's a bit harder because you might get charges on your disks that generate anywhere from mV to kV and electronic devices won't like kV. Can you tell me if your sensitive devices are there to detect charge states on the disks, and you expect sometimes to get dangerously (for the circuits) high potentials?
Dear Tony Maine,
Unfortunately i cannot cover the components with shielding as they are phototransistors and LEDs that need to be in view of each other.
it could be possible to partially cover them.
The disk is part of a wheel arrangement, purpose of the components is measure the rotation of the wheel as in an optical encoder.
The components are a about 0.5mm from the disk.
Best regards,
Davide Bortolami
Dear Matthias and Dear Marian,
I will check out the availability of more conductive ABS, but since the device incorporate an antenna and a radio transmitter it may shield or absorb radio waves.
I will also check out other materials that could be suitable and have nearer dielectric costants, but i'm afraid i will have to keep ABS for cost reasons.
Thank you for your help and best regards,
Davide Bortolami
Dear Davide, you can shield with optically transparent conductive polymers - these exist because otherwise flat panel phone screens won't work . . . Or even very fine wire mesh. Incidentally, I don't think phototransistors or LEDs will suffer from ESD as long as the impedances from any of their electrodes to ground is not too large. ESD affects field effect devices where the impedances are large and a few million electrons can make a big difference to voltages!
Best wishes!
There have been some good suggestions in this discussion. However, using two materials the same will not prevent triboelectric charging. Also, optoelectronic components can be susceptible to ESD damage, although this is usually from more substantial sources like charged human body or metal objects. Whether a strong "brush" discharge from charged insulators could cause damage would depend on the sensitivity of the components, and the strength of the discharge that could arise.
I like Tony Maine's idea of a mesh screen between the components and the charged insulators. This would have to be conductive and earthed otherwise it too would become a source of ESD. It might not have to be a fine mesh, a relatively coarse mesh or a metal sheet with a hole for light transmission could work. This solution could possibly be designed to screen the components against electrostatic fields (which are unlikely to be a problem to the components) but more importantly would tend to draw any discharge that does happen, to the screen. There remains a question whether any transient current due to a discharge could cause electromagnetic interference to the electronic system.
The shield has to be earthed, but at one point only, near or at the 0V line feeding the optoelectronics. I doubt if the discharge will be strong enough to cause electromagnetic interference. If it is, then you may have to remove the photosensors and use fibre optic links. These are all standard methods of eliminating interference in industrial and military electronics systems, some of which are subject to stray fields maybe a million times greater (e.g. radar transmitters) than you will get in your system. They do work!
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