Many customer wonder why hydrostatic level sensors fail due to lightning strikes, even if 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 kind of hydrostatic level sensors, were first installed into reservoirs and lakes to monitor level, the sensor would become burned or destroyed after 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 understand is that the effect of a lightning strike is considerably different depending on how close to the pressure sensor the lightning strikes in to the ground or installation. It 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 undoubtedly be incinerated by direct hits.
However, more distant hits will only improve 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 power will then dissipate in to the ground via the particular level probe and therefore destroy or damage its electronics. This may equally be the case when overhead wires have 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. As Annihilate of short nature of the voltage pulse, a component may be fitted 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 path 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 isn’t sufficient or no lightning protection is integrated within the hydrostatic level sensor, then the electronics will take the entire amount of energy of the voltage pulse and fail.Therefore the protection is only as effective as the earth grounding provided by the user.
In outdoor applications, where submersible pressure transmitters are generally used, WIKA provides an optionally integrated lightning protection inside the level sensors. The sensor electronics will then 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.
Take a look at the profiles of WIKAs submersible pressure transmitters LH-20 and LH-10.
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