For most applications, single-lead probes are the best choice. When a GWR transmitter is used in a chamber, the microwave signals are guided and contained within the chamber. This results in a stronger signal from the fluid surface, which is an advantage for turbulent or low-dielectric fluids.
Single-lead probes are less susceptible to build-up and are more tolerant of coating than twin or coaxial probes. In very low-dielectric but clean fluids, such as liquefied gases, (for example LNG), a coaxial probe may be used.
In boiler feedwater heaters and boilers where the pressure is greater than 400 psi (27.6 bar), the dielectric properties of the steam tend to reduce measurement accuracy. Special probes to compensate for this situation may require a longer chamber top end (Figure 1b).
Help is available from GWR manufacturers in the form of application support and installation advice. For users who wish to take all of the risk out of ordering their level measurement products, manufacturers can supply a chamber and GWR as a complete solution. This approach avoids many potential problems.
For example, Emerson offers a combined 9901 chamber and GWR solution designed to meet industry safety standards (Figure 4). Ordering a chamber and GWR device together means they have been consolidated at the factory before shipping, ensuring they are correctly sized. This approach provides the user with a complete measurement solution ready to install out of the box, reducing installation and commissioning times.