Hydrostatic level sensors (also referred to as submersible pressure transmitters) are very often installed in outdoor applications, primarily in the water and wastewater industries, where open bodies of water, deep wells or boreholes are monitored. A good connection to ground is essential when installing hydrostatic level sensors, since no grounding or poor grounding can result in destruction or damage to the level sensor.
Common failures from improper grounding
Hydrostatic level sensors in outdoor applications are connected via cables to the PLC or routed to local telemetric systems. These cables can act like an antenna, conducting electromagnetic or aerial voltage spikes down the wires to the sensor, causing an overload in the electronics, and thereby premature failure. The media that is measured may itself store energy like a capacitor. This is caused by lightning strikes, electrical surges, or simply static electricity. If there is not a sufficiently low impedance ground connection for the level sensor, this may cause voltage surges that flash through the electronics, causing them to overload and burn out.
Even if the voltage difference is too low to cause an overload of the electronics, it can cause electrolytic action due to the difference in voltage potential. This electrolytic action causes the metal housing material of the hydrostatic level sensor to be ‘eaten away’ over long-term operation. Electrolytic corrosion pits will form in the material, which can cause the diaphragm or housing to perforate, ultimately causing premature failure of the level sensor. This may be mistaken for chemical corrosion, but is in fact caused by the difference in voltage potential between the sensor and the surrounding liquid. Without a good ground, the sensor becomes a sacrificial anode and is inevitably eaten away.
How to ground and protect a hydrostatic level sensor
WIKA level sensors are available with optionally integrated lightning protection, which acts on dangerous differences in the voltage potential between electronics, cabling and transmitter body. This routes any harmful voltages to ground before they can damage the internal circuitry. However, if the grounding for the transducer is poor, it will still have nowhere else to go but into the electronics or body of the sensor, causing a premature failure.
In the case of metallic and plastic tanks, any isolated metal parts should be connected to a common ground with an impedance of less than 100 Ohms. In applications onboard ships, where metal tanks are always present, all the different ground potentials should be linked to the ship’s main ground point during docking. In lakes and reservoirs, a low-impedance connection to ground may be hard to achieve, but will be well worth the effort as it saves the hydrostatic level sensor electronics from failure. On artificial constructions or rock sites, even long copper spikes driven into the ground may not give a low enough impedance to ground. To solve this, earthing grids can be embedded into the ground to achieve a suitable resistance to ground.
Grounding of hydrostatic level sensors is a basic requirement for the reliable operation of level sensors, especially in outdoor applications, where overvoltage spikes and surges due to lightning strikes can occur regularly. Failure to provide adequate grounding can result in the failure of the level sensor.
Meeting the challenges of tank obstructions interfering with radar
Level Measurement & Control
One of the most challenging applications for non-contacting radar level transmitters is measuring level in tanks with internal obstructions, such as agitators, heating coils, pipes, ladders or baffles. Rosemount non-contacting radar level transmitters from Emerson feature an advanced solution that enables accurate and reliable level measurements in tanks with obstructions.
Read more...A fresh approach to dairy processing VEGA Controls SA
Level Measurement & Control
Ensuring the quality and safety of milk throughout the production process is of the utmost importance in the dairy industry. The VEGABAR pressure transmitters are suitable for hygienic applications. They are an asset in the dairy industry and have been used with success for measuring the milk level and the process pressure in storage tanks.
Read more...Multiphase level measurement Mecosa
Level Measurement & Control
The measurement of more than two phases or of interfaces that are not clearly defined poses a number of challenges for measurement technology. Radiation-based measuring systems such as Berthold‘s EmulsionSENS master these problems.
Read more...Simple and efficient level measurement in the mining, minerals and metals industries Endress+Hauser South Africa
Editor's Choice Level Measurement & Control
Measuring devices in the mining, minerals and metals industries face the challenge of varying material states and long distances in measurement height. Endress+Hauser’s answer to these challenges is the new Micropilot family.
Read more...Level measurement of an acid dosing tank at a WWTP
Level Measurement & Control
Ferric chloride and other acids are essential chemical substances in water and wastewater treatment. To control the dosing of acid solutions, an Australian wastewater treatment plant uses a special container to store, mix and add these chemicals. The company opted in favour of KROHNE’s OPTIWAVE 1540 radar level transmitter
Read more...Powering sub-Saharan Africa’s energy future VEGA Controls SA
Level Measurement & Control
Crude oil storage plays an important role in the energy infrastructure of sub-Saharan Africa. The management of crude oil storage in comes with numerous challenges, including safety concerns, environmental conditions and infrastructural limitations.
Read more...Unique industrial asset monitoring solution WIKA Instruments
Sensors & Transducers
WIKA WikaPredict offers a unique industrial asset monitoring solution, combining advanced sensors and artificial intelligence. As a leader in predictive maintenance, it helps clients enhance operational performance and increased efficiency.
Read more...Level measurement of leachate from sewage sludge humification KROHNE
Level Measurement & Control
A municipal utility in eastern Germany operates a state-of-the-art wastewater treatment plant with sustainable sludge treatment. The ultrasonic signal was being partially deflected by the wind, leading to frequent false measurements and inefficient process workflows. The problem was solved by replaced the ultrasonic level sensor with KROHNE’s OPTIWAVE 1540 non-contact radar.
While every effort has been made to ensure the accuracy of the information contained herein, the publisher and its agents cannot be held responsible for any errors contained, or any loss incurred as a result. Articles published do not necessarily reflect the views of the publishers. The editor reserves the right to alter or cut copy. Articles submitted are deemed to have been cleared for publication. Advertisements and company contact details are published as provided by the advertiser. Technews Publishing (Pty) Ltd cannot be held responsible for the accuracy or veracity of supplied material.
printer friendly version