The cable telecommunications industry developed the principle of measuring levels guided microwave, or TDR (Time Domain Reflectometry, time domain reflectometry) to detect a break in its extensive cable network. When transmitting a radar pulse through the cable, as long as the feedback signal for your travel needs, varies as open or short circuit has different impedances (ie, distance). Annually, this method is used for measuring levels (see fig. 11) in the presence of large amounts of dust, because the ultrasonic measuring tools may fail because of high dust content and level indicators sounding free microwave can not be used due to the dry solids do not reflect the emitted energy.
Figure 11. Example on sound level meter. TDR technology differs from conventional radar that emits microwave pulses in a wide frequency band (200 kHz to 1.2 GHz). TDR technology uses electromagnetic micro-impulses that travel through cable (guided waves) and are reflected due to a sudden change in dielectric constant. In level measurement, the change in the value of the dielectric constant corresponds to the air / product. The distance D to the product surface is proportional to the flyback pulse, where C is the speed of propagation. It is important that the pulses emitted power is very low (less than 1 microwatts) and are guided by what little energy is dissipated. For this reason, the intensity (amplitude) of the signal that returns will be almost the same if the product level between 3 m and 10 m from the flange.
Just as in measuring ultrasonic and microwave method is used envelope curve in the measurement technique each wire TDR probe is represented by 512 digital points, regardless of the length of it. Collect a sample of the behavior of reflected pulses at each point of the probe and the accumulated information about the sampling cycle is processed and converted into information about the level of the product. The flyback principle guided microwave is used for solid level indicators of up to 20 m and is known for Levelflex. The low power of the radar energy can be installed securely in containers and silos both non-metallic and metallic without risk to humans or the environment. Not require any licenses. Another difference between the microwave level gauges in open space and TDR instruments is that in the first, the same structure, other possible assemblies in the bin and the end of the wire probe also detected and properly return more impulses the product level. For this reason we carried out the so-called "map probe that confirms that the pulse received is the product level (see fig. 14). This "mapping" is usually done at the factory for specified lengths of the probe and it is only necessary if special assemblies or reduced the length of the probe.
measuring instruments guided microwave level serve a wide variety of solids up to a grain size of 20 mm and dielectric constant values \u200b\u200bof 1.8 or higher. Not affected by moisture or by changes in the composition or by pressure or temperature. The presence of large amounts of dust, steam, adhesions, acoustic noise or angle of repose of the product does not affect the measurement. The indicator has no moving parts to wear out or break down. The output is usually 4-20 mA, but the system can be integrated with the RS 485, HART and PROFIBUS protocols or with the Fieldbus Foundation. The indicator is capable to make measurements over a range extending from 30 cm. from the process connection up to 35 cm from the end of the weight of the sensor or the mounting point (see fig. 12).
Just as in measuring ultrasonic and microwave method is used envelope curve in the measurement technique each wire TDR probe is represented by 512 digital points, regardless of the length of it. Collect a sample of the behavior of reflected pulses at each point of the probe and the accumulated information about the sampling cycle is processed and converted into information about the level of the product. The flyback principle guided microwave is used for solid level indicators of up to 20 m and is known for Levelflex. The low power of the radar energy can be installed securely in containers and silos both non-metallic and metallic without risk to humans or the environment. Not require any licenses. Another difference between the microwave level gauges in open space and TDR instruments is that in the first, the same structure, other possible assemblies in the bin and the end of the wire probe also detected and properly return more impulses the product level. For this reason we carried out the so-called "map probe that confirms that the pulse received is the product level (see fig. 14). This "mapping" is usually done at the factory for specified lengths of the probe and it is only necessary if special assemblies or reduced the length of the probe.
measuring instruments guided microwave level serve a wide variety of solids up to a grain size of 20 mm and dielectric constant values \u200b\u200bof 1.8 or higher. Not affected by moisture or by changes in the composition or by pressure or temperature. The presence of large amounts of dust, steam, adhesions, acoustic noise or angle of repose of the product does not affect the measurement. The indicator has no moving parts to wear out or break down. The output is usually 4-20 mA, but the system can be integrated with the RS 485, HART and PROFIBUS protocols or with the Fieldbus Foundation. The indicator is capable to make measurements over a range extending from 30 cm. from the process connection up to 35 cm from the end of the weight of the sensor or the mounting point (see fig. 12).
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