Guided Wave Radar
Level Measurement: How to Make the Best of GWR
For example, Emerson’s transient terminal block is designed to provide a high degree of protection against transients and works in conjunction with a good earth ground to direct the surge away from the electronics. Good earth grounding for externally induced transients can be achieved using a conductive wire between the flange and a ground rod or grid.
Electrical noise from nearby equipment, for example variable speed drives, can be a particular problem with non-metallic silos as it may be picked up by the probe. This can be addressed by using filters to remove most common EMI from rotating equipment, motor controllers and other sources. There is no issue with metal silos as the metal walls shield the probe from the noise.
Why an Adequate Grounding is Needed for Level Measurement
Inadequate grounding can result in signal noise that makes it difficult to detect the actual peak; it can also lead to electronic failure since the transient protection relies on good grounding in order to function properly. With metal tanks, it is important to ensure a ‘metal to metal’ connection between probe and tank. Also the size of the grounding wire is important for proper installation since it provides a direct path to earth. Larger diameter cables and short distances give the best results and users should refer to the installation manual to ensure that the manufacturer’s recommendations are being followed. For a vessel with possible internal surges, such as static discharge, one or more internal ground wires between flanges provide an alternative path.
Non-metallic tanks pose special problems for GWR level transmitters as surges will often enter the transmitter through the probe. It is therefore important that an external ground wire is used in these applications. It is also important that the contents of a non-metallic tank are effectively grounded. If a tank is filled from the bottom, this can usually be achieved by grounding through the piping. If the tank is filled from the top, the contents may not be properly grounded and it may be necessary to install a grounding rod covering the entire height of the tank.