The Radar level transmitter is known well for the accuracy and low maintenance it offers to the users. In the metal industry, molten metal furnaces have high temperatures and gases which call for special level measurement technology. Ultrasonic level transmitter fails to work here due to conditions unfavourable to their operations. Also, the presence of gases and foam disrupts the ultrasound waves and the readings are misleading and inaccurate. On the other hand, other level measurement technologies like float switches have a high maintenance cost as they need to be replaced frequently. Since radar level transmitters use radio waves or electromagnetic waves, they are independent of external factors such as gases, pressure, high temperatures, and material of the furnace.
Radar level transmitter uses radio waves or electromagnetic waves to send signals and receive the echo back to measure the level of the liquid, solid, molten metals, or any substance for that matter. Since electromagnetic waves are not affected by the medium and instead work on the speed of light, they are more robust, versatile, and accurate in terms of operations. The operation of a radar level transmitter is similar to that of an ultrasonic level transmitter. However, it has a radio wave module, an antenna, and a gauging setup. The gauging setup basically comprises of high temperature gauging system. The high temperature level measurements are done using the non-contact or Frequency Modulated Continuous Wave method. Another alternative Radar level transmitter method is the contact-based or Guided Wave Method. This method is not apt for molten metals as the high temperature level transmitter is damaged due to coming in direct with the liquid surface.
To measure the level of molten metal, the antenna sends an electromagnetic wave based on the FMCW method. The echo is received back by the high temperature level transmitter or radar level transmitter and the time taken to travel forth and back to the molten metal level transmitter is used to calculate the distance between the sensor and the surface of the molten metal. This is digitally converted to predict the level of the molten metal. Unlike the ultrasonic level transmitters, the radar level transmitters do not have a dead zone or free charge zone where it is unable to catch the signal as it sits very close to the receiver itself.
The radar level transmitter works optimally for high temperature level measurements because they are least affected by the internal pressure, gases, condensation, high temperature, and foam. The factor that influences the electromagnetic waves is the dielectric number of the medium through which the waves will travel. Apparently, radio waves can also travel through the vacuum. The dielectric number simply measures the charge the medium carries when electromagnetic waves hit it or how much reflection will it provide to the waves. For example, water has a high dielectric charge (of 80). This makes water a good reflector of electromagnetic waves. Various gases have different dielectric numbers which indicate their ability to reflect the radio waves. Yet, the electromagnetic waves have little effect on their accuracy with changing dielectric numbers. Hence, this is one of the biggest reasons for many liquid level measurements to be done via radar level transmitters.
The antenna is used to send the microwave signals. To increase the longevity of life and prevent corrosion due to extreme environmental conditions, the antenna is often coated with enamel. Most antennas are horn-shaped to provide a wider beam and low-frequency signal.
The position of the radar system is usually at the side of the furnace. The side of the furnace has a lower temperature and has low susceptibility to deposits on the radar device compared to direct placement on the top perpendicular to the surface of molten metal. This also helps with easier maintenance of the device.
Features of Radar Level Transmitter for Molten Metal Level Measurement
- The Radar Level transmitter offers high accuracy of ±0.5mm.
- The installation is simple and easy at the top.
- The system operates without any contact
- The environmental factors like gases, humidity, foam, medium, and dust
- The setup does not require any readjustment in case of a change of liquids
- The measuring range can be easily adjusted
- The operation is unaffected even under high temperatures
Additionally, the radar level transmitter and also be equipped with high temperature level transmitter to measure and gauge the temperatures. The Radar level transmitter may also be used to measure the slag level over the molten metal.
To measure the level of slag and molten metal. The device is set up at the side of the furnace. A deflected beam is sent to hit the surface of the slag. The deflection is done through an additional device. The signal hits the edge of the slag and penetrates further to reach the surface of the molten metal. The deflection from the surface of the furnace and from the surface of the liquid is received back by the level transmitter. The deflection compensation device adjusts the time taken to travel from medium to slag and further from slag to molten metal and the level is measured.
Considerations
- The tank design should be considered at the time of installation as it can affect the deflection of waves
- The minimum dielectric number of 1 should be maintained to sustain the accuracy of the results.
- Consider the blocking distance or the dead zone
- For optimum results, ensure there are no turbulent surfaces within the furnace or it might disrupt the waves and the readings.
Radar Level transmitters are highly accurate and easy to operate level transmitters and work great for molten metal level measurements as they are optimal for high temperatures. The cost of installing the device is on a higher side compared to its counter parts such as ultrasonic and laser level transmitters. However, their high limitations and high maintenance cost make them unfit for use in the metallurgical industry. Not just this, the inability to yield precise level measurements makes them unviable for use in real-world scenarios. The antennas have a wide range of frequencies and can easily be controlled to use for varying depths and levels of liquids without any adjustments to be done with the setup physically.
The non-contact technology reduces the cost of repair and ensures safety even in extreme conditions. Also, the absence of any moving parts increases the longevity of the device.