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From the Lab: Lightning Protection for the PT-500

Lightning strikes can disable electrical equipment if not properly designed.

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.

The PT-500 submersible pressure transducer has been designed and thoroughly tested to withstand 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:

  • Voltage levels of 500, 1000 and 2000 were applied to the PT-500
  • At each voltage level the pressure transducer was subjected to 8 voltage spikes per second for 2 seconds
  • The characteristics of each test voltage were 1.2 ms rise time and 50ms pulse width
  • A total of six combinations of “Line to Line” and “Line to Ground” were tested at each voltage level and polarity

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, feel free to check out our submersible level sensor for yourself, and let us know if you have any questions.

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