Every year there are at least 20 million cloud-to-ground lightning strikes (source:noaa.gov). Lightning can generate millions of volts and hundreds of thousands of amps per strike.
When lightning hits the ground, a near or direct hit will usually severely damage or destroy a sensor. With an indirect hit, a current pulse will travel a great distance before dissipating into the ground, and while less destructive than a direct hit, can wreak havoc on electrical instrumentation.
For the most part, our sensors are installed in relatively protected environments. However, the PT-500 submersible level sensor is often installed in outdoor environments, providing pump control in sanitary lift stations or monitoring leachate tanks in landfills. It is, therefore, exposed to electrical surges due to nearby lightning strikes.
Both the clean liquids and dirty liquids version of the PT-500 have been designed and thoroughly tested to withstand transient power surges from lightning strikes. We use a testing standard known as IEC 61000-4-5, which is set by the International Electrotechnical Commission. To state it plainly, it tests whether an instrument can withstand electrical surges.
In the words of the IEC, standard IEC 61000-4-5:
“relates to the immunity requirements, test methods, and range of recommended test levels for equipment to unidirectional surges caused by over voltages from switching and lightning transients.”
Let's break down the testing procedures:
In other words, we shock it real good – a bit like a mad scientist.
After the test is completed, the 4/20mA output cannot have shifted more than the specified accuracy of 0.50% of full scale, and must function normally.
The result of the Surge Protection testing was that the PT-500 submersible level sensor met all performance requirements at all of the test voltages.
Do you have any horror stories about equipment failure due to lightning strikes? If so, we'd love to hear them! In the mean time let us know if you have any questions.
