Two-wire 4-20 mA electronics for a fiber optic vortex shedding flowmeter
US4742574A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 3, 1986 |
| Grant date | May 3, 1988 |
| Priority date | — |
| Expiry date | Feb 3, 2006 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08C19/02
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A method and apparatus for processing optically generated signals to form a two-wire 4-20 mA signal comprises generating a control signal having pulses at a selected frequency to drive a light emitter which generates light pulses, transmitting the light pulses to a light detector over a transmission line having variable attenuation to form a sensor signal and amplifying the sensor signal in an operational amplifier. The variations and attentuations follow a process variable to be measured. To save power the operational amplifier has a low-current mode into which it is switched whenever no pulse is present in the sensor signal. The amplifier is switched into its high-current mode only when a pulse is present in the sensor signal. Switching is controlled by the control signal for the light emitter. Peaks in the signal from the operations amplifier are sampled and held and then subject to low pass filtering to remove the selected frequency componnent and leave a cyclic filtered signal. The operational amplifier also receives a signal to drive it toward ground using a feedback clamping signal which changes slowly with respect to the cyclic filter signal. The filter signal is used to tr…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.