| ??? 04/15/08 14:32 Read: times |
#153394 - Connect the shield to analog ground! Responding to: ???'s previous message |
Dear Mahmood,
the shield should never be connected to any high impedance input of chip. Think of ESD, for instance! As you want to shield analog signals the only point to connect the shield is analog ground. Only when being connected low ohmically to analog ground, the shield can effectively shunt high frequency noise arround the chip to ground. When being connected to any high impedance input pin of chip, EMI is injected directly into the chip, which is highly unwanted. What you do with protective earth depends on your power supply: If your power supply is "safety class I", you must connect everything that is touchable to protective earth. This inlcudes not only the chassis but usually also signal ground, if a "safety class I" transformer is used. But even then, the shield must be connected to analog ground at first. Happily, many todays scales are low current consuming devices only needing a tiny wall plug transformer. These scales are usually designed in "safety class II" technique, not needing any connection to protective earth. To avoid any "touching potentials", the chassis of these scales are covered by plastics, so that nothing metallic can be touched. In this case do not connect protective earth to anything inside! It's not only useless, but also forbidden. The shield of inside analog cables (to the load cell for instance) must be connected to analog ground. 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 |