Magnetic flow meter earthing in non conductive pipe systems

Establishing a process ground is one of the most important installation details. Proper process grounding ensures that the sensor and fluid are at the same potential so that only the induced flow signal is measured. The flow signal is connected to a differential amplifier that is electrically isolated from the case of the transmitter. The process of grounding provides a stable ref-erence for this differential amplifier. In the majority of applications, the best and most stable reference is earth ground itself. By connecting the mag meter sensor, the fluid, and the reference for the amplifier to a stable, noise free reference point, the user is ensured of getting the best performance.

Ground rings are required when the piping adjacent to the mag meter does not provide a good electrical connection to the fluid. Ground electrodes are an integral part of the sensor, so installation is easier and less expensive, particularly when “exotic” materials are required. Ground rings provide a larger surface area of connection to the process fluid, and limit the effects of the conductivity of the adjacent piping, which is important for wafer style sensors. Therefore ground rings should be installed in the following situations:

• Mercon magnetic flow meters installation data sheet
• Magnetic flow meter process grounding magnetic flow meter grounding arrangements
• Basic process grounding
• This applies to the instrumentation aspect of the installation & addresses different issues to the safety grounding described below
• Magnetic flow meter measurement circuit
• Ground rings vs. Ground electrode
• The fluid conductivity is less than 100uS/cm
• Wafer style sensors installed in non-conductive piping or lined piping. Such as PVC & CPVC
• Applications that may cause a coating or build-up on the bottom of the pipe
• Electrolytic process or cathodic protection, these applications have special requirements contact sales@merrimancontrols.com for assistance

To prevent hazards to operating personnel, electrical equipment must always be installed and wired as per local electrical code. For AC powered equipment, this usually takes the form of connection of the case of the equipment to earth ground. If the transmitter is integrally mounted to the sensor, this automatically connects the sensor to earth ground as well. It is common that the adjacent piping to the mag meter will provide a connection to earth ground. It is important that if both earth ground connections are established, the impedance between them must be very low. If the impedance between these earth ground connections is high, it can result in a high current through the coil shield wire.