Many customer wonder why hydrostatic level sensors fail because of lightning strikes, even though they ordered a level sensor with integrated lightning protection. Focusing on how the lightning protection works and how lightning strikes affect hydrostatic level sensors is essential in resolving this confusion.
When submersible pressure sensors, a particular type of hydrostatic level sensors, were first installed into reservoirs and lakes to monitor level, the sensor would become burned or destroyed following a lightning storm or bad weather periods. This prompted much research into the aftereffect of lightning storms on the instrumentation in reservoirs and the cabling to and from the website.
What lightning protection really means
The first thing to comprehend is that the result of a lightning strike is considerably different depending on how close to the pressure sensor the lightning strikes into the ground or installation. It really is fair to say that no level sensor will survive a primary or very close nearby lightning strike, where usually the whole cabin including all installed electronics will be incinerated by direct hits.
However, more distant hits will only improve the Voltage differential by for instance 1500 Volts. If a local lightning strike raises the electric potential of a reservoir, the level sensor might provide the shortest method for the raised voltage and current to earth. The power will then dissipate into the ground via the particular level probe and thus destroy or damage its electronics. This might equally be the case when overhead wires take a hit.
So how exactly does lightning protection in level sensors work?
However, sensors could be protected from these lightning strikes by installing or integrating a transient voltage protection into the hydrostatic level sensor. Due to the short nature of the voltage pulse, an element may be suited to or integrated into the sensor that acts on rising differences in voltage potential. If the voltage goes above say 50 Volts, this lightning protection can short-circuit the electronic circuit to ground, allowing a way to ground for the surge and protecting the electronics up to the utmost specified voltage potential.
The component would normally operate in a non-conductive state, but will undoubtedly be conductive for a voltage transient, allowing the voltage spike to flow harmlessly to ground. If the bond to earth is not good enough or no lightning protection is integrated within the hydrostatic level sensor, then your electronics will take the entire amount of energy of the voltage pulse and fail.Which means protection is only as good as the earth grounding supplied by the user.
In outdoor applications, where submersible pressure transmitters are commonly used, WIKA offers an optionally integrated lightning protection inside the level sensors. The sensor electronics will be protected from local power surges and transient high voltage. Lightning protection is really a combination of protection within the instrument and an excellent low impedance earth grounding.
Have a look at the profiles of WIKAs submersible pressure transmitters LH-20 and LH-10.
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