| ??? 10/17/05 12:02 Read: times |
#102482 - ground loops, oversampling Responding to: ???'s previous message |
Donald said:
The serial communication will consist of a PC listening to the serial port. I will be taking ten readings per second so I will be able to send individual readings between measurements. The PC will not be talking to me except to abort a test. This sounds good. There will be very little external analog electrical circuitry. The output ramp is scaled to 1 to 5 volts and sent to a pneumatic servovalve. the servovalve uses it to regulate a pressure input to a pneumatic to hydraulic pressure amplifier. This output is sent to a pressure transducer only for local servovalve feedback and also to a hydraulic flow amplifier. That output is applied to the specimen and also to the pressure transducer that I read and send to the PC. When I detect that the specimen has burst I end the test. Both the servovalve and the transducers are proprietary units powered by 24 VDC. The transducer that I read has a 0 to 5 volt output. Here a good grounding management is important too. I guess that some of the devices need a connection of their metallic housings to safety ground? Then, take care, that no ground loops are formed by the signal grounds, if they are also connected to saftey ground somehow. If you are really wanting 16bit resolution, then ground loops are deadly. Back when I was designing instrumentation in the eighties the A/D converters were either Successive Approximation (fast but very noise sensitive) or Integrating Dual Slope (slow but relatively noise tolerant) This will be my first use of a Sigma/Delta converter. How is their noise succptibility? Due to their oversampling performance noise susceptibility is absolute minimum. Compared to standard conversion schemes, which often suffer from unsatisfying anti-aliasing filtering and which get the signal frequency band contaminated by high frequency noise folded into it, sigma/delta conversion is widely immune against this phenomen. Further noise reduction can be provided by using a simple single pole low pass filter at input of ADC. Another advantage of sigma/delta conversion scheme and its very high conversion rate (oversampling) is, that quantization noise is distributed beyond the frequency band of interest. The total noise energy remains constant, but spreading it over a wider spectrum, the amount in the frequency band of interest is reduced. So, very low noise levels can be optained by using this scheme. Kai |
| Topic | Author | Date |
| ADUC848 project getting started | 01/01/70 00:00 | |
| Some hints... | 01/01/70 00:00 | |
| More! | 01/01/70 00:00 | |
| Bible? | 01/01/70 00:00 | |
| The "book" is 3 general chapters that re | 01/01/70 00:00 | |
| ADUC848 Project: details for hints | 01/01/70 00:00 | |
| ground loops, oversampling | 01/01/70 00:00 | |
| You have a head start, most have proble | 01/01/70 00:00 | |
| Is 10 readings per second sufficient? | 01/01/70 00:00 | |
| required sampling rate | 01/01/70 00:00 | |
| Thanks, but... | 01/01/70 00:00 | |
| books? | 01/01/70 00:00 | |
| books? | 01/01/70 00:00 | |
| Avoid That | 01/01/70 00:00 | |
| C on a PC? | 01/01/70 00:00 | |
| OK | 01/01/70 00:00 | |
| Starting C on the '51 with no prior C kn | 01/01/70 00:00 | |
Point taken | 01/01/70 00:00 |