Ultrasonic sensors (Figure 3) use piezo crystals to generate a mechanical pulse which is launched from the sensor membrane.

GWR is more efficient when comparing signal transmission with installation concerns. Whereas a radar signal is sent out at an angle with an increasing footprint and the reflections returning are not being guided back to the transmitter. Being guided down and back along with the smaller footprint allows for greater efficiency and less interaction with intrusions or dust. The evaluation comparison between GWR technology and radar comes down to efficiency.Īs the signal is transmitted from the GWR transmitter it has a profile similar to the size of a football that football is being guided by the rod or rope. When the DC is low and the disturbances are many, or where there is heavy dust present, GWR technology can be an excellent choice. The lower the DC of the material, the less reflected energy, thus reducing the range of measurement. The DC of the material being measured has a significant effect on the measuring range. The transmitter divides the time down plus the return time by two, and then multiplies by the speed of light to calculate the level. The energy reflects back to the transmitter when it encounters a change in dielectric (air has a DC of 1.0 and most bulk solids are above 1.4). GWR uses an approximately 1.2 GHz pulsed radar signal that travels down a guide rod (Figure 2) or cable, making it a “contact” device that is, the rod or cable contacts the solid. The density or DC-along with installation location, height of the silo, and the presence of disturbances such as supports, mixers, dust, condensation, and other factors-determine the best choice for each application. TOF devices use either the reflection based on the density of the material in ultrasonic systems, or the reflection based on the dielectric constant (DC) of the material for radar instruments. Measuring the level in silos used to hold bulk solids (Figure 1) can pose challenges. Guided wave radar (GWR), ultrasonic, and pulse radar are time-of-flight (TOF) technologies used to detect level by measuring the time it takes for a microwave or ultrasonic signal to be sent, reflect from the surface of the material being measured, and return to the instrument.

Api 2350 4th edition