Hot:21892013-09-08 14:46:18 From: FTD Automation Instruments
In Non-contact level measurement, radar technology application has obtained rapid development in recent years. Transducer of Ultrasonic level meter is the eye, while high frequency head and antenna is the eye of radar level meter in, echo processing is level meter brain. Radar level meter inherited ultrasonic level meter echo processing technology.
Electromagnetic waves of Radar level meter is emitted, then reflecting by the measured medium, echo quality reflects the material level meter application effect. Echo quality is defined as the minimum echo amplitude (in the worst condition echo amplitude) than the largest noise amplitude (false echo, multipath reflection wave of amplitude). Echo quality numerical is bigger, level meter application effect is good.
Echo intensity is mainly affected by the following factors:
Dielectric constant of Propagation medium is more stable, more conducive to spread. Radar wave is electromagnetic wave, electromagnetic wave is free from propagation medium effect during the process of transmission , only effected by the dielectric constant. This is the radar technology and ultrasonic technology major difference.
The more smooth of Measured medium surface, the bigger of dielectric constant , and the better for echo reflection.
So consider field condition, should pay special attention to the two aspects:
(1) Distribution of air dielectric constant between antenna and measured medium
(2) measured medium surface satiation and its dielectric constant.
Radar level meter advantage is: do not affect by air fluctuations, along with distance attenuation shorter, stronger penetrating power.
1) influence the performance of the radar is dielectric constant, theoretically in vacuum radar attenuation is minimum, when attenuation material existing in the air of radar, such as: high dielectric properties of dust powder (graphite, ferroalloy, etc.), water vapor is very big, measuring distance and effects should be affected.
2) Measured medium volatile gas will be gathered in the antenna, also water vapor in the antenna, these will affect radar wave emission, even stopping radar wave emitting.
3) Measured medium dielectric constant can't be too small.
4) Although temperature and pressure have little effect on radar, but the radar antenna is made by the material, the use of materials and seal structure is related to the pressure and temperature of the actual situation.
Radar level meter has become the mainstream products in the market, and low frequency radar level meter although has the advantages of relatively cheap cost, but in the main application fields, they have been washed out gradually. From the application of ultrasonic level meter, we know that to get better echo, transducer operating frequency is about 40 KHZ, wavelength about 9 mm, then transmitted wave open Angle should be 7 ° - 8 °. The higher the frequency, the smaller of open Angle, but the smaller range. From ultrasonic analogy, radar level meter to obtain the effect of echo, the working frequency should be 26 GHZ, at this time, the wavelength is 11 mm. When using diameter for 100 mm horn, may obtain 7 ° - 8 ° open Angle launch wave. If radar work frequency is 6 GHZ, it was equivalent to ultrasonic work frequency for 10 KHZ. And the work frequency for 10 KHZ ultrasonic level meter in the material level measurement of each index is not ideal, in particular, is not suitable for solid material level measurement. Compared with low frequency radar, high frequency radar has the following advantages:
1) high frequency radar level meter (mainly referring to 26 GHZ and 24 GHZ) has the high energy ,the small beam Angle (general Φ 95 horn antenna beam Angle is 8 o, and 6 GHZ low frequency pulse radar horn antenna diameter for Φ 246, beam Angle for 15 o), antenna size is small, the advantages of high accuracy.
2) and 26 GHZ radar wave length 11 mm, 6 GHZ radar wave length 50 mm, when radar measuring bulk material level, radar wave reflection mainly from the diffuse material, diffuse reflection strength and material is proportional to size, and inversely proportional to the wavelength, and most of the bulk material diameter is far less than 50 mm, this is why now 26 GHZ radar is bulk material level measurement of the best choice.
3) in some small diameter height and short canister applications, 6 GHZ long radar antenna (300-400 mm) virtually increases the blind area (about 600 mm), with 6 GHZ radar directional difference (open Angle) in a small tank will produce the multipath reflection; 26 GHZ radar frequency high frequency, antenna short, directional well, to overcome the shortcomings of 6 GHZ radar, it is suitable for small tank measurement.
4) due to the bad environment and long time using, radar antenna will deposit dirt, moisture, etc., and 26 GHZ radar antenna is small, we can add radome to greatly improve the dirt, moisture influence; 6 GHZ large radar antenna , adding radome is very difficult. And instrument is heavy, difficult to clean.
5) with 26 GHZ radar well direction, a lot of bad working condition can be easily isolation, also we can put radar out of vessels to measure.
At present, the price of 26 GHZ radar level meter is almost the same as 6 GHZ radar level meter , this promotes the 26 GHZ radar level meter application. We may foresee, 6 GHZ radar level meter market share will be greatly reduced.
With the development of technology, we are looking forward to higher frequency (such as: 90 GHZ), more small open Angle (such as: 2 ° and 3 °), smaller volume of radar level gauge will be invented.
Edit by FTD Automation Instruments (www.ftdinstruments.com)