| ??? 04/07/05 17:01 Read: times |
#91181 - Not as bad as initially thought. Responding to: ???'s previous message |
Initially, my very first try with the zapper, I could really mess with the uC and LCD. When I tried another of the 3 controls that have been returned to me with all the same symptoms, it withstood numerous zaps. I was really baffled by this, when I noticed that the mounting screws for the connector coming out of my control box were in place on the second unit and not the first. I put the mounting screws back in the first unit and it was also able to withstand numerous zaps. When reading some back posts I found this:
A much better approach is to connect the cable shield to the enclosure in such a way, that the formed Faraday cage is uninterrupted, means that any ESD event hitting the enclosure can directly flow to cable screens, not being able to penetrate enclosure and run across the whole board!! And if enclosure is connected to signal ground at this cable entry point, where the cable screens are connected to enclosure, then the enclosure can furthely work as shield for the electronics sitting on PCB. It might be useful sometimes to isolate the enclosure to signal ground for mains frequency, and connect the enclosure to signal ground by the help of capacitor. But for high frequencies THERE MUST ALWAYS BE a low impedant connection between signal ground and enclosure. Just what a capacitor or a direct connection yield. But, NEVER insert an inductivity. Then enclosure can not act as a shield anymore. And if this insertion was made, then only to correct a former mistake, according the motto, or better hope, that two mistakes give something that is correct again.... Kai So I began to examine the grounding situation with our system. I did not design this and am no longer in contact with the person that did. I'm not an engineer, but have learned enough to keep things up and going and to implement other hardware to suit new purposes. This is what we have: The control cabinet (Chassis) is safety grounded. The one control cable leaving the box has the shield grounded to the chassis at one end and connected to the cutting machine at the other end. It's 3 feet long. 10 conductor. 6 for stepper motor, 2 for AC solenoid, 2 for switch, 2 unused. We have a step down transformer 110 VAC-> 18VAC which goes to a bridge rectifier, this goes to our PCB. The raw DC voltage goes to supply the stepper motor. It is also runs through a 1N4001 diode in series with 100 ohm resistor to drop the voltage to a tolerable level for the 5V regulator. This input voltage is filtered with a 330uF electrolytic and the output from the regulator is filtered with a 33uF electrolytic. There is no physical connection of the DC ground to either the chassis or the safety ground. The PCB is mounted to the cabinet with metal stand-offs. The mounting pads on the PCB are isolated from any connections, however one is very close to the crystal for the uC. It looks to me like our system it close to what Kai describes above, but I'm probably overlooking something. Now, the system is less susceptible when the cabinet is properly closed and cable connected, but is still susceptible to multiple very rapid zaps on the cabinet, especially to the mounting screw closest to the crystal. Zapping the cutting machine itself didn't have any negative effects. However zapping the cable connector housing on the machine end would sometimes give a false signal to the control, but this was not one of the symptoms complained about. I tried connecting the cable shield to chassis ground, with and without a .1 uf cap - no difference I tried connecting chassis ground to DC ground on PCB, with and without a .1 uf cap - no difference Jon |
| Topic | Author | Date |
| What do you think could happen if... | 01/01/70 00:00 | |
| The 10k from RST to GND | 01/01/70 00:00 | |
| Random resets.. | 01/01/70 00:00 | |
| Dogma. | 01/01/70 00:00 | |
| Oh yea ? | 01/01/70 00:00 | |
| Hmm | 01/01/70 00:00 | |
| brown outs | 01/01/70 00:00 | |
| Obscure | 01/01/70 00:00 | |
| RC Reset circuits. | 01/01/70 00:00 | |
| Something more to it ... | 01/01/70 00:00 | |
| ad wars between Maxim and Microchip | 01/01/70 00:00 | |
| Cutting teeth... | 01/01/70 00:00 | |
| recommend brown out detectors | 01/01/70 00:00 | |
| Which depends on for what.. | 01/01/70 00:00 | |
| built-in reset | 01/01/70 00:00 | |
| Re: Built in brown out? | 01/01/70 00:00 | |
| Better than I did.... | 01/01/70 00:00 | |
| Thanks, Michael. | 01/01/70 00:00 | |
| Why | 01/01/70 00:00 | |
| Other stuff ? | 01/01/70 00:00 | |
| many reasons | 01/01/70 00:00 | |
| Thats not correct. | 01/01/70 00:00 | |
| speak with forked tongue | 01/01/70 00:00 | |
| I agree | 01/01/70 00:00 | |
| re: dogma | 01/01/70 00:00 | |
| ESD events and EMI | 01/01/70 00:00 | |
| Re: Random resets. | 01/01/70 00:00 | |
| Lets not reject the obvious! | 01/01/70 00:00 | |
| no R | 01/01/70 00:00 | |
| RC-circuits are bullshit!! | 01/01/70 00:00 | |
| RC-circuits are bullshit!! | 01/01/70 00:00 | |
| Reset Capacitor | 01/01/70 00:00 | |
| You missed the question! | 01/01/70 00:00 | |
| Why guessing? | 01/01/70 00:00 | |
| RE:Why Guessing | 01/01/70 00:00 | |
| Timing | 01/01/70 00:00 | |
| Update | 01/01/70 00:00 | |
| not necessarily the reset | 01/01/70 00:00 | |
| Other derivatives | 01/01/70 00:00 | |
| if no cap | 01/01/70 00:00 | |
| No Cap | 01/01/70 00:00 | |
| not just a cap, but the right cap | 01/01/70 00:00 | |
| Which cap? | 01/01/70 00:00 | |
| depends | 01/01/70 00:00 | |
| Yes Cap | 01/01/70 00:00 | |
| directly | 01/01/70 00:00 | |
| RE:Directly | 01/01/70 00:00 | |
| yes | 01/01/70 00:00 | |
| Absolutely ! | 01/01/70 00:00 | |
| Update - ESD Problem? | 01/01/70 00:00 | |
| some ways | 01/01/70 00:00 | |
| some ways - more detail please | 01/01/70 00:00 | |
| details | 01/01/70 00:00 | |
| Car induction coil | 01/01/70 00:00 | |
| ESD Problem | 01/01/70 00:00 | |
| Physical Separation | 01/01/70 00:00 | |
| Few Ideas | 01/01/70 00:00 | |
| Re: Few Ideas | 01/01/70 00:00 | |
| Check your external ground | 01/01/70 00:00 | |
| Ya. | 01/01/70 00:00 | |
| now that you are willing | 01/01/70 00:00 | |
| RE:Now that you are willing | 01/01/70 00:00 | |
| alot easier when you know what your look | 01/01/70 00:00 | |
| Not as bad as initially thought. | 01/01/70 00:00 | |
| ground loop | 01/01/70 00:00 | |
| RE: Ground Loop | 01/01/70 00:00 | |
| sound | 01/01/70 00:00 | |
| RE: Ground Loop | 01/01/70 00:00 | |
| It is a loop AND | 01/01/70 00:00 | |
| It's a loop and a flop | 01/01/70 00:00 | |
| no shield can help you there | 01/01/70 00:00 | |
| Kind of machine | 01/01/70 00:00 | |
| so your testbench setup should be OK | 01/01/70 00:00 | |
| Failures | 01/01/70 00:00 | |
| in that case | 01/01/70 00:00 | |
| Materials | 01/01/70 00:00 | |
| could still be ground | 01/01/70 00:00 | |
| Noise resistance | 01/01/70 00:00 | |
| you will not find that | 01/01/70 00:00 | |
| What can be found? | 01/01/70 00:00 | |
| tough these days | 01/01/70 00:00 | |
| Glue ? | 01/01/70 00:00 | |
| No Glue | 01/01/70 00:00 | |
| lesse some pictures. | 01/01/70 00:00 | |
| LOL | 01/01/70 00:00 | |
| Nope | 01/01/70 00:00 | |
| Let the fun begin! | 01/01/70 00:00 | |
| Confession | 01/01/70 00:00 | |
| Confession | 01/01/70 00:00 | |
| Ah. | 01/01/70 00:00 | |
| Not that bad | 01/01/70 00:00 | |
| HAr to see but | 01/01/70 00:00 | |
| Wiring & Filter | 01/01/70 00:00 | |
| Maybe a little better pictures here | 01/01/70 00:00 | |
| nice | 01/01/70 00:00 | |
| Oops - try again | 01/01/70 00:00 | |
| Uh Oh | 01/01/70 00:00 | |
| Yep | 01/01/70 00:00 | |
| Don't ground both ends of shield | 01/01/70 00:00 | |
| bonding | 01/01/70 00:00 | |
| RE: Bonding | 01/01/70 00:00 | |
| Useless.... | 01/01/70 00:00 | |
| Better Pix yet? | 01/01/70 00:00 | |
| Re: Better Pics Yet? | 01/01/70 00:00 | |
| DETAILS... | 01/01/70 00:00 | |
| Nothing hiding here! | 01/01/70 00:00 | |
| !!!!! | 01/01/70 00:00 | |
| I don't think so. | 01/01/70 00:00 | |
| !! | 01/01/70 00:00 | |
| Grounding. | 01/01/70 00:00 | |
| Grounding | 01/01/70 00:00 | |
| Prahlads points | 01/01/70 00:00 | |
| Clarification | 01/01/70 00:00 | |
| Clarification | 01/01/70 00:00 | |
| Update | 01/01/70 00:00 | |
| au contraire | 01/01/70 00:00 | |
| The answer may be on the horizon | 01/01/70 00:00 | |
| not the voltage, but the change | 01/01/70 00:00 | |
| Have a look see | 01/01/70 00:00 | |
| I do not know how good | 01/01/70 00:00 | |
| 7805 Starving | 01/01/70 00:00 | |
| it will go HOT | 01/01/70 00:00 | |
| Heatsink | 01/01/70 00:00 | |
or it's possible | 01/01/70 00:00 |