Using the algorithm of the tip of the probe with the Levelflex M, the Endress+Hauser company

The Guided microwave (TDR) level transmitter Levelflex M Endress+Hauser is capable of measuring the level in a silo or reactor under the most difficult process conditions. The algorithm of the tip of the probe (patented by E+H), this level of last generation transmitter can determine what level there are in the interior of the tank but there is no reflection from the surface of the product of process. This feature ensures a measure of reliable in the most unfavourable conditions of process level.

Levelflex M is a level transmitter based on the time of return of the pulses of microwave to measure the distance from the sensor installed in the upper part of the deposit up to the surface of the product in the interior of the same. An electromagnetic pulse is launched and guided through a rod or metallic cable that acts as the wave transmission line.

When this wave perceives a discontinuity in the means of transport, e.g. a sudden change of dielectric constant between the means of transport "air" and the "product" of process, part of this signal is reflected and analyzed by the level transmitter. The distance (level) is calculated by dividing between the time measured between the transmission of a pulse and the return of the reflected pulse and multiplying by the speed of light.

Part of the energy that has not been reflected by the product of process will reflect on the end of the probe level.

Each product has a dielectric. The dielectric in vacuum is "one" and any other product shall be referred to this gap. Electromagnetic waves moving at a speed known in a vacuum. When these waves move in another medium speed changes, indeed, any product that has a greater "one" dielectric will reduce the speed of displacement of the wave. A hydrocarbon (e.g., diesel or LPG) is considered to have a low dielectric, about 2. This value is still a 100 by 100 superior of the vacuum.

Each level transmitter has a length of cable or rod known. The end of the rod or cable gives a reflection of the end of the Guide wave (addition to the reflection that is received from the surface of the product). Depending on the energy reflected on the surface of the product's process, the electromagnetic wave will continue their movement through the cable or rod guide waves and there will be a reflection of energy (to a greater or lesser extent) at the end of the probe. However, reflection received since the end of the probe will a drift over time, because the electromagnetic wave is moving through the product process. This "drift in time" between the reflection of the tip of the probe into the air and through the product, will directly depend on the quantity of product to be above the tip of the probe.

The algorithm of calculation in the Levelflex M is adjusted so that own electronics computes the dielectric of the product using the drift in the time that has the sign of the end of the probe when it is covered by product. When the reflection of electromagnetic wave on the surface of the product is lost, the electronics detect it and automatically switches to use the algorithm of the tip of the probe until recurrence is a reflection on the surface of the product. This treatment of the reflections guarantees a measure of reliable in any condition of process level.

The dielectric of each product is always different, and also changes with the temperature, humidity and sometimes with the pressure. In practice, each product even with the same name has a different dielectric. This is the reason by which the capacitive probes are less accurate than the Levelflex M, since they do not compensate for the changes that have the dielectric of the product. The speed of propagation of electromagnetic waves are will greatly reduce the larger the dielectric of the product. The most important thing is that the Levelflex M, calculate the value of the dielectric of the product (using the algorithm of the tip of the probe) and measured the level of the product in the silo or warehouse with precision. Levelflex M refreshes every 0.5 seconds of level measurement and the dielectric constant which is the product of the process.

As explained above, the Levelflex M determines the level that there is a silo or tank in two ways. First using the reflection of electromagnetic waves on the surface of the product and second using the signal from the tip of the probe. During a filled tire or a liquefying, the great very atmosphere that is created in the interior of the silo generates much "noise" in the measurement of level. The reflected signal of the electromagnetic wave in these circumstances with a product of low dielectric and much background noise is very low. Still, as Levelflex M uses the two level measurement methods described above, it will always give a safe and precise measurement of the level under any condition of process.

The same goes in applications for liquids with low dielectric (hydrocarbon or solvent) than subjected to agitation, temperature and pressure can facilitate that the reflection of the wave on the surface of the product will go away. At that time the algorithm of the tip of the probe will give you the possibility to continue measuring the level with reliability.