So how exactly does lightning protection in hydrostatic level sensors work

Many customer wonder why hydrostatic level sensors fail due to lightning strikes, even if they ordered an even sensor with integrated lightning protection. Understanding how the lightning protection works and how lightning strikes affect hydrostatic level sensors is important 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 in to the effect of lightning storms on the instrumentation in reservoirs and the cabling to and from the site.
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 is fair to say that no level sensor will survive a direct 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 raise the Voltage differential by for instance 1500 Volts. In case a local lightning strike raises the electric potential of a reservoir, the level sensor may provide the shortest method for the raised voltage and current to earth. The energy will then dissipate into the ground via the particular level probe and thus destroy or damage its electronics. This may equally function as case when overhead wires have a hit.
How 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 fitted to or built-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 around the maximum 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 sufficient or no lightning protection is integrated within the hydrostatic level sensor, then your electronics will take the full quantity of energy of the voltage pulse and fail.Therefore the protection is only as effective as the earth grounding provided by the user.
In Fight , where submersible pressure transmitters are generally used, WIKA offers an optionally integrated lightning protection in the level sensors. The sensor electronics will be protected from local power surges and transient high voltage. Lightning protection is a mix of protection within the instrument and a good low impedance earth grounding.
Have a look at the profiles of WIKAs submersible pressure transmitters LH-20 and LH-10.
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