| ??? 01/18/10 15:51 Read: times |
#172546 - agree Responding to: ???'s previous message |
Kai said:
70mV signal and 20V common mode voltage demands the use of a very very precise differential amplifier, not showing any temp and long term drift of common mode rejection. With 1% toleranced voltage dividers about 40dB common mode rejection is the best you can achieve, resulting in about 200mV common mode noise at the input of ADC! Kai, as you point out that the divider scheme wouldnt have enough CMRR , but differential-ADC has around 120-130dB.Seeing your point and reducing the current drive the CMV is approaching about 8V cant reduce the current any further , any insight . Galvanic isolation is the last resort , as xducer(loadcell ,sorry stefan I forgot to mention it earlier) is onboard so I dont expect much RFI etc . Oliver, you mean to lift the ADC GND proportionally along with a resistor in its GND path .But that will offer an impedance in its GND connection? or I dont follow you . Regards -Ap |
| Topic | Author | Date |
| Isolating xducer | 01/01/70 00:00 | |
| not even a way | 01/01/70 00:00 | |
| noise | 01/01/70 00:00 | |
| I wouldn't do that... | 01/01/70 00:00 | |
| agree | 01/01/70 00:00 | |
| when within specified range!!! | 01/01/70 00:00 | |
| why 8V or 20V | 01/01/70 00:00 | |
| no specs violated | 01/01/70 00:00 | |
| that is TOTALLY irrelevant | 01/01/70 00:00 | |
| Jumping to conclusions | 01/01/70 00:00 | |
| AC modulating the bridge excitation voltage? | 01/01/70 00:00 | |
modulating the excitation | 01/01/70 00:00 | |
| make it simple at start | 01/01/70 00:00 | |
| making it | 01/01/70 00:00 | |
| o, i see... | 01/01/70 00:00 | |
| from my experience with loadcells ... | 01/01/70 00:00 | |
| what is exactly "xducer" ? | 01/01/70 00:00 | |
| Offsetting a signal | 01/01/70 00:00 | |
| Yes but...? | 01/01/70 00:00 | |
| Error analysis and budget | 01/01/70 00:00 | |
| Common Mode suppression | 01/01/70 00:00 |