Comparison of radar surface transmitter with ultrasonic transmitter
Ultrasonic level sensor is a non-contact surface measurement method that uses sound waves to determine the extent of the measurement process. Ultrasonic transmitters work by sending an audio wave generated by a piezoelectric converter to the measuring media. The device measures the time it takes to measure the reflected sound wave to the transducer. Successful measurement depends on the reflection of process materials in a straight line to the converter. However, there are several effects that affect the return signal. Factors such as dust, heavy vapors, tank blockage, surface turbulence, foam and even surface angles can affect the feedback signal. For this reason, the conditions that determine the characteristics of sound should be considered when using ultrasonic measurements.
Other problematic aspects of an ultrasonic surface sensor include the following:
- Sound must travel through a medium (usually air)
- The absence of air molecules prevents the propagation of sound waves
- Sound waves must be sent and received in a straight line
- Reflective surfaces should be smooth (eg non-turbulent / non-turbulent conditions)
- Foam and other debris collected on the surface of the liquid that absorbs sound waves and prevents the sound from returning to the sensor.
- Ultrasonic units are usually plastic with a maximum temperature of 140 degrees Fahrenheit (60 degrees Celsius).
- Variable process temperature may cause incorrect readings
- Ultrasonic devices are not intended for severe pressure limitations
- Maximum working pressures should not exceed 30 PSIG (2 times)
- Ultrasonic surface sensors must be mounted in a predictable environment
- Vapor, condensation humidity, and other contaminants that alter the speed of sound through the air greatly affect the accuracy of the return signal.
The most popular advantage of airborne measurement principles such as ultrasonic, radar or laser measurement is the fact that the measurement signal never comes into contact with the product being measured. But if you think about it, this “reality” is not entirely accurate. Use ultrasonic, for example: When the transducer releases sound energy, it travels through the air at 1212 feet per second to reach its target (ie, the liquid level). Like other “non-contact” level measurements, at some point the measurement signal must be in contact with the liquid level before beginning its return journey to the sensor. This not only explains why the air quality between the sensor and the liquid surface can be problematic, but also why the liquid surface quality needs to be considered. Any disturbance that goes back and forth in its path interferes with the actual information measuring the actual level of the signal. It is important to understand that ultrasonic transmitters, if used properly, provide a reasonable solution. Remember, an ultrasonic transmitter is as good as an received echo.
Radar level sensor
A radar level sensor is a method of measuring the contact surface that uses a probe to guide high-frequency, electromagnetic waves as they pass through a transmitter into the medium being measured.
GWR is based on the principle of amplitude timing reflection (TDR), which is an electrical measurement method that has been used for decades in various industrial measurement applications. One of its first applications was the location of cable damage. However, in level measurement, TDR has only been used for a little over a decade. Using TDR, a low-power electromagnetic pulse is conducted along the probe. When the pulse reaches the surface of the environment being measured, the probe pulse energy is reflected back into the circuit, which then calculates the amount of liquid from the time difference between the transmitted pulse and the reflected pulse. The sensor can output the analyzed surface as a continuous measurement reading through its analog output, or it can convert values to free-position switching output signals.
The radar level sensor is suitable for a variety of level measurement applications including
Unstable process conditions
- Changes in viscosity, density or acidity are not correct
- Boiling surfaces, dust, foam, steam does not affect the performance of the device
- Rotating liquids, impeller mixers, aeration tanks
Severe operational constraints
- Radar level sensor performs well in extreme temperatures up to 600 degrees Fahrenheit (315 degrees Celsius)
- Pressure bearing up to 580 PSIG 40 bar
Beautiful powders and important liquids
- Vacuum tanks with cooking oil used
- Dyes, latex, animal fats and soybean oil
- Saw dust, carbon black, titanium tetrachloride, salt, grain
One of the most common misconceptions about radar level sensors is the effect of product production on the probe. Do you think that if you trap a mass of product along the probe or a product along the entire length of the probe, this signal will cause an unpleasant detection of the actual liquid level. This is not really the case with advanced radar level sensor technology. The radar level sensor signal has a very large detection area around the probe that covers 360 ˚ area over a few feet. When this pulse energy is in contact with a mass of product in the probe, the signal returns and is analyzed to see if this amount of fluid is real. Because the liquid surface is always larger than the smaller mass attached to the probe, the signal return is larger, the liquid surface is easily identifiable. Advanced algorithms developed over the past decade have made this form of contact surface measurement an ideal solution for even the most important fluid applications. The benefits of a radar level sensor in the surface industry are endless. Unlike older technologies, radar level sensors measure readings independent of propertiesProvides chemical or physical in the contact environment. In addition, the radar level sensor works well on liquids and solids.
The following diagram compares the important features between an ultrasonic surface sensor with a radar level sensor and wave conduction.