Hello, I am working on a project that requires me to weigh small, pebbles. This is done by attaching a plate onto the end of a load cell, having them hit the plate and then fall off.
Before I test it again in the field I want to make sure I don’t burn out any more components. I have read some things online and am wondering what is the best approach. I’ve heard things such as ‘ground everything directly to power source’, ‘do not ground at multiple points’, ‘use static guard spray’, ‘create a static shield box’ or ‘change plate material from aluminum to plastic or wood’. Wondering what the best approach would be and steps to go about solving it. I am a ‘seasoned newbie’ with respect to electronics.
There were grounding issues and it caused shocks and even burned out some of my electronics.
That has absolutely nothing to do with static or grounding issues. Those components were more likely burned due to miswiring. This whole grounding and static thing is a red herring. If the components were wired correctly they would not have burned. We have had almost zero posts for component damage due to grounding or static issues . The grounding issues that resulted in damage were cases of gross negligence or inexperience. There is nothing wrong with being static conscience or grounding conscience but let's not confuse the issue which more than likely was miswiring. There are thousands and thousands of people using the same modules who are not reporting component damage.
Is it possible for you to install your electronics in a metal box ?
Look, I'm never claimed to be "Mother Teresa".
I just don't think we should patronize a newbie ( "seasoned" or "unseasoned" ) by allowing them to believe that the damage was caused by something else.
Your whole set-up is a classic example of transferring static charges from one object to another. Whatever the particles are that you are dropping onto the metal plate, they will carry a charge from their source to the plate they strike and will build up on the plate.
What are you using to hold and control the volume of material? This source and all associated devices must be connected to the Arduino system ground and to a real earth ground.
If direct connection is not possible, use a 1 meg ohm resistor to connect them together.
This source and all associated devices must be connected to the Arduino system ground and to a real earth ground.
I don't see how a pebble would have a static charge but even if it did, and it landed on the plate, how would that explain damage to electronics that are wired properly. The plate is a load cell and as such , SHOULD be electrically isolated from the electronics. You COULD make the plate metalic and ground it.
There is no Earth GND because there is no enclosure and the electronics is battery powered. I see no reason to bring Earth GND into the discussion unless you are suggesting a copper stake driven into the ground (possibly less than the usual 3 to 6 feet) and a thin copper braid tied to the plate. Then you could discuss Earth GND because it is a true Earth GND. Three modules running off a battery pack don't have an Earth GND. All they have is the circuit GND. Frankly, I don't see why the plate needs to be metal but if it was it should be tied to circuit GND but I wouldn't call that an Earth GND. Where is the static supposed to be coming from any way ? (the user shuffling on carpet before dropping the pebbles ?)
I'm sorry. I don't get it. What makes this a classic static transfer example ? If the pebbles are loaded into a can with solenoid powered trap door on the bottom that pulls back allowing only one pebble to drop, and the pebble holder is metal and tied to the same ground as the plate with the same type of copper braid, how do explain the presence of any static ? (if the pebbles are grounded before dropping onto a grounded plate)
Materials rubbing against each other develop a charge. The amount of charge is dictated by the material and whether or not it's conductive. Metal is conductive, but pebbles are not. Thus a charge will develop.
Dude, read that post again. It's SPAM. (I agree with it but that doesn't make it any less spam)
That might be because there is very little in the OP's original post that really supports static charge as the real problem.
OP
There were grounding issues and it caused shocks and even burned out some of my electronics.
Agreed. The OP said nothing to link the damage to the static. Another poster said this was a classic static transfer example because pebbles are non-conductive and therefore hold a charge. I can neither confirm nor deny this.
The flow of granules of material like sand down a plastic chute can transfer charge, which can be easily measured using a multimeter connected to metal foil lining the chute at intervals, and can be roughly proportional to particulate flow
That's from the Wikipedia article on static electricity.
Yeah I agree that there's no guarantee that OP's problems are due to static electricity, but as has already been mentioned (and demonstrated by the Wiki page) this is a classic example of a situation where it will be a problem. You've gotta give the OP the benefit of the doubt.
Finally, suggesting that the load cell should already be electrically isolated from the aluminum plate ignores the 10kV+ you're dealing with. You can't expect the load cell to insulate from that kind of voltage.
Finally, suggesting that the load cell should already be electrically isolated from the aluminum plate ignores the 10kV+ you're dealing with. You can't expect the load cell to insulate from that kind of voltage.
The flow of granules of material like sand down a plastic chute can transfer charge,
The OP is talking about pebbles.
This is done by attaching a plate onto the end of a load cell, having them hit the plate and then fall off. (setup1)
Ok, but let's be accurate about this. We work with voltages over 12kV occassionally where I work and we have no problem providing isolation with Nomex paper. Kapton tape also offers some dialectric properties but nowhere near Nomex paper. You can't be suggesting that if the plate is aluminum foil over a sheet of the proper thickness of Nomex paper that the 10kV could still damage the load cell underneath all that ? Besides , if the plate was grounded , the charge would be shunted to ground on impact anyway.
@OP,
Is there some reason you have not posted a photo of this setup ?
Make a template drill the holes . add the plastic standoffs , connect a ring terminal to the box with a screw and the connect the other end of that wire to the arduino GND. Only one connection to the box is necessary if everything shares the same ground. Make sure you allow room for USB cable and any others.
Unrelated to the OP and static electricity issues... Double beam load cells are usually not sensitive to the location of the "c.g." of applied force, within reason...such as if the c.g. is within the recommended platform size (for the 10kg load cell, it's a rectangle 250 mm x 350 mm centered on the platform/load cell attachment point).
But the OP's (undimensioned) sketch appears to illustrate a significant eccentricity, perhaps far beyond the recommended platform size. If the force and/or eccentricity is too large, one or more of the four strain gauges could be stretched beyond their limits (or the aluminum components of the load cell itself could be damaged).
Might be the reason the 2014 setup failed.
JoelVin:
I want to add that the setup works and is reading correctly until the point that the pebbles start crashing down on the plate. There is about 3 kgs of pebbles on the plate at any one time.
And perhaps a reason the current setup doesn't work after the "pebbles start crashing down on the plate."
Does the setup give the expected force measurement with a "static" load (that is, "stationary" or "not moving" load) on the plate that is equivalent to the sum of the weight of the "pebbles" and the force due to the change in their momentum? (This equivalent static/stationary load must be positioned so that it generates the same moment (force x distance) on the load cell as the dynamic load...)
Paul_KD7HB:
Your whole set-up is a classic example of transferring static charges from one object to another. Whatever the particles are that you are dropping onto the metal plate, they will carry a charge from their source to the plate they strike and will build up on the plate.
Yeah true. Kind of like a van de graaf generator effect going on here.