Here’s a stumper for ya’all.
I have an ultrasonic switch that is used to determine the density of various products as they accumulate in a steel hopper. Problem is, some of these materials generate a lot of static cling to the sidewalls of the hopper as they slide down it.
I’m getting premature triggering of my ultrasonic switch - and it’s caused by one of two possible variables. Could be the composition of the material, but it could also be related to the static field itself interfering with the detection equipment. The actual box with the guts (circuit board, oscilation doohickey, etc.) is insulated and 5 feet away from the area where the field is being generated, but the emitter and receiver of the sonic pulses are obviously right on the hopper itself.
I’m trying to eliminate one of these variables, and the manufacturer of the switch is extremely slow to respond. Google is giving me very vague and nonspecific information.
Maybe you’ll just groan and google it for me properly (I might be a google dummy but I don’t think so…), or maybe somebody here knows! In any event I’ll be greatly indebted to whoever helps me and I’ll give them 90% of my third lottery ticket winnings in 2050.
Sounds like the static is giving you noise problems with the detector instrumentation. There are effective established techniques for eliminating noise in systems where the receiver has access to the transmitted signal - such as in an ultrasonic send/return setup - but if this one just sends out a simple blip and uses the raw amplitude of the received ultrasonic signal to estimate density then it will be vulnerable to both acoustic and electromagnetic noise. Objects holding a static charge that are bumping against each other will be redistributing charge amongst themselves, and that generates tiny sparks. These are miniature bolts of lightning, and each one will produce a small acoustic shock wave that has frequency components that extends up into the ultrasonic. They’ll also produce a little electromagnetic pulse that could interfere with the electronics.
I suspect that the reason the manufacturer is being slow to reply to your concerns is that you’re not the first customer to have noticed this susceptibility.
Your best bet in the short term is to try and reduce the static level. Earthing (grounding) the steel hopper would be a good place to start, if it’s not already grounded. Ideally you’d want a big thick copper wire connecting the hopper to the planet, usually by means of a long metal stake driven into the ground outside. If there’s a handy copper water pipe nearby that is continuous copper all the way to the underground pipe (i.e. no plastic sections), then this would serve for diagnostic purposes. Don’t connect to gas pipes - gas and sparks don’t play nicely together. Don’t connect directly to the mains outlet earth either, as potential wiring faults mean that the earth terminal could be at live potential, and you don’t want a live hopper. It is, however, acceptable practice to connect to mains earth via a 1 megohm resistor - special mains plug adaptors are available to enable this.
Ion generators can be used to dissipate static charges, but that’s getting pretty hardcore. Google “antistatic”, “anti-static” or “anti static” and you’ll find a vast array of products out there. It’s a big problem in many industries, though the bias is towards protection of delicate electronic devices.
I have a static issue with my Dyson vacuum cleaner, as the dry dust and cat fluff whirrs around inside an insulating plastic cylinder, making an effective van der graaf generator that charges the plastic surface and discharges tens of thousands of volts through me the next time I touch it. I need to make a faraday cage vacuum-cosy for it, as one day it’s going to zap my PC or something.
Hope this helps. If it does, I’ll take you up on the 2050 lottery ticket…
Thanks Fridgemagnet.
Update for anyone who cares: They got back to me - basically saying yep, the static is likely causing “noise” in the circuit. Since this system is looking for variances on the order of 1/2 of a volt, the potential fluctuations caused by the static might be pushing it occasionally too far to one side of the range it’s set to detect.
He explained the specifics of how it works normally, and it had to do with the wave (kinda like on an oscilloscope) changing when the density in front of the emitter/receiver changed. The static interference being carried in the shielding of the cables that run to the emitter/receiver is what’s causing the problem, since the shielding is grounded to the housing, and the housing is mounted to the hopper.
Solution - install a static mitigation device INSIDE the hopper to prevent static buildup and it should help.
ETA: he also said nobody’s ever brought this up before. and electrical engineers are terrible liars…aren’t they?
Did he mean that they lie frequently, or that they’re terrible about it when they do? I might need this answer fast… 