Guided Wave Radar
A Guided Wave Radar is a type of level transmitter which utilizes a microwave pulse to detect liquid's depth. It avoids physical movement.
Microwave sensors are ideal for use in moist, vaporous, and dusty environments as well as in applications in which temperatures and pressures vary. Microwaves (also frequently described as RADAR), will penetrate temperature and vapor layers that may cause problems for other techniques, such as ultrasonic. Microwaves are electromagnetic energy and therefore do not require air molecules to transmit the energy making them useful in vacuums. Microwaves, as electromagnetic energy, are reflected by objects with high conductive properties, like metal and conductive water. Alternately, they are absorbed in various degrees by 'low dielectric' or insulating mediums such as plastics, glass, paper, many powders and food stuffs and other solids.
Guided Wave Radars can measure in narrow confined spaces very successfully, as the guide element ensures correct transission to and from the measured liquid. Applications such as inside stilling tubes or external bridles or cages, offer an excellent alternative to float or displacement devices, as they remove any moving parts or linkages and are unaffected by density changes or build up. They are also excellent with very low microwave reflectivity products like liquid gasses (LNG, LPG, Ammonia) which are stored at low temperatures/high pressures, although care needs to be taken on sealing arrangements and hazardous area approvals. On bulk solids and powders, GWR offers a great alternative to radar or ultrasonic sensors, but some care needs to be taken over cable wear and roof loading by the product movement.
One perceived major disadvantage of microwave or radar techniques for level monitoring is the relatively high price of such sensors and complex set up. However, price has reduced significantly over the last few years, to match those of longer range ultrasonics, with simplified set up of both techniques also improving ease of use.
See also
- wikipedia:Level sensor#Microwave
- http://www2.emersonprocess.com/siteadmincenter/pm%20rosemount%20documents/00813-0100-4811.pdf