| ??? 10/22/08 22:14 Read: times |
#159269 - LVDT Responding to: ???'s previous message |
Stefan Kanev said:
Hi Steve,
Reading this topic, i'm finding what dummie i am in this circuitry (LVDT). AFAIK one must measure AC voltage on secondary winding to determine value of displacement. What is usually practice to measure AC with resolution 14..15 bits. What conversion speed is used? How primary AC is used in ADC , is there something like ratiometric measurement? regards Stefan Hi Stefan, A good LVDT is, as you say, a ratiometric device. We use a phase sensitive rectifier to demodulate the output of the LVDT and a good reference to derive the drive signal and drive the ADC. The sampling rate of the ADC is about 100 times slower than the drive signal frequency. The mean current in the LVDT is kept constant by a feedback loop derived from an absolute rectifier, and an averaging circuit then compared to the reference and a correcting signal used to set the level of the driving oscillator. The reference feeds the ADC ref in as well. We currently use a precision unity gain op-amp (INA 105) and a couple of analogue switches (DG311) to build the phase sensiive rectifier. Steve |
| Topic | Author | Date |
| Function Generator IC | 01/01/70 00:00 | |
| Better? | 01/01/70 00:00 | |
| Maxim | 01/01/70 00:00 | |
| Maxim unavailable | 01/01/70 00:00 | |
| DDS? | 01/01/70 00:00 | |
| Better? .5% -1% THD with discrete solution? | 01/01/70 00:00 | |
| Wein bridge? | 01/01/70 00:00 | |
| Simple wont do ... | 01/01/70 00:00 | |
| LVDT driving | 01/01/70 00:00 | |
| High performance can be simple | 01/01/70 00:00 | |
| Tuning | 01/01/70 00:00 | |
| DDS again | 01/01/70 00:00 | |
| Design. | 01/01/70 00:00 | |
| What frequency? | 01/01/70 00:00 | |
| frequency | 01/01/70 00:00 | |
| Err | 01/01/70 00:00 | |
| DDS again | 01/01/70 00:00 | |
| THD | 01/01/70 00:00 | |
| THD | 01/01/70 00:00 | |
| reference | 01/01/70 00:00 | |
| Yes, but at what cost? | 01/01/70 00:00 | |
| About 4 bucks | 01/01/70 00:00 | |
| Better? In what way? | 01/01/70 00:00 | |
| 6 dollars | 01/01/70 00:00 | |
| Gee ... That isn't so bad! | 01/01/70 00:00 | |
| Tuning | 01/01/70 00:00 | |
| Hand-tuning is not cheap! | 01/01/70 00:00 | |
| Drift | 01/01/70 00:00 | |
| how does drift impact the manpower requirement? | 01/01/70 00:00 | |
| Notes | 01/01/70 00:00 | |
| Amplitude , tempco | 01/01/70 00:00 | |
| Precision | 01/01/70 00:00 | |
| Precision ... | 01/01/70 00:00 | |
| at that rate | 01/01/70 00:00 | |
| to Steve | 01/01/70 00:00 | |
| LVDT | 01/01/70 00:00 | |
| power/energy meter IC | 01/01/70 00:00 | |
energy meter IC | 01/01/70 00:00 | |
| at that rate | 01/01/70 00:00 | |
| Filtering? | 01/01/70 00:00 | |
| It will remove SOME of the distortion | 01/01/70 00:00 | |
| have you seen this? | 01/01/70 00:00 | |
| I am afraid | 01/01/70 00:00 | |
| Simple` | 01/01/70 00:00 | |
| DTMF Genarator | 01/01/70 00:00 |