| ??? 04/19/08 15:16 Modified: 04/19/08 17:12 Read: times |
#153711 - Two enclosures, on safety class I requirements Responding to: ???'s previous message |
David said:
As a matter of practical observation, I have determined that load cell screens MUST be connected solidly to the enclosure at point of entry (assuming the case is indeed a Faraday shield). As long as we have no picture of Mahmoods application I recommend the following: If Mahmood has to use a metallic enclosure because of saftey class I requirements (use of protective earth), then the best shielding is to have two Faraday cages, an inner and an outer. The inner to shield the electronics against EMI and high frequency noise coming from the AD7730 chip itself and an outer enclosure to shunt ESD and EMI from outer world (Mahmood mentioned a near radio station) arround the circuit to protective earth. The shield of cable of load cell should be part of the inner enclosure. The mechanics, where the load cell is mounted on should also be part of the inner enclosure. All these inner shields should be connected to the analog ground point, which is under the AD7730. The outer (metal) enclosure should have of a certain distance to the inner enclosure. It must also be connected to the central ground point near the AD7730, but in a manner, that ESD hittÃng the outer enclosure is not injected into the circuit, but shunted arround it to protective earth. Not under any circumstances must the shield of cable of load cell provide the connection of outer enclosure to analog ground of circuit, because then all ESD and EMI hitting the outer enclosure would be directly injected into the circuit. Kai |
| Topic | Author | Date |
| Load cell shield | 01/01/70 00:00 | |
| Earth ground | 01/01/70 00:00 | |
| where is Earth ground ... | 01/01/70 00:00 | |
| yes but.. | 01/01/70 00:00 | |
| Why Ain- is grounded... | 01/01/70 00:00 | |
| read datasheet of AD7730 | 01/01/70 00:00 | |
| it's correct | 01/01/70 00:00 | |
| try Yourself and tell us result | 01/01/70 00:00 | |
| Connect the shield to analog ground! | 01/01/70 00:00 | |
| I tend to forget | 01/01/70 00:00 | |
| Good idea! | 01/01/70 00:00 | |
| Analog gnd | 01/01/70 00:00 | |
| Exactly! | 01/01/70 00:00 | |
| Ferrite beads trick! | 01/01/70 00:00 | |
| Loadcell Shield | 01/01/70 00:00 | |
| ground planes | 01/01/70 00:00 | |
| Hhm... | 01/01/70 00:00 | |
| re: hmm | 01/01/70 00:00 | |
| interesting | 01/01/70 00:00 | |
| RF | 01/01/70 00:00 | |
| RF GSM | 01/01/70 00:00 | |
| I use use this | 01/01/70 00:00 | |
Walkie talkies | 01/01/70 00:00 | |
| Load Cell Screens | 01/01/70 00:00 | |
| JUST FOR RECORD | 01/01/70 00:00 | |
| Two enclosures, on safety class I requirements | 01/01/70 00:00 | |
| No proof, of course... | 01/01/70 00:00 | |
| Load cell cable problem | 01/01/70 00:00 | |
| fix it | 01/01/70 00:00 | |
| Problem is | 01/01/70 00:00 | |
| so make Digital Load Cell | 01/01/70 00:00 | |
| good idea | 01/01/70 00:00 | |
| give picture | 01/01/70 00:00 | |
| Screens and cables. | 01/01/70 00:00 | |
| "Fixed Structure" | 01/01/70 00:00 | |
| Fixed? | 01/01/70 00:00 |