Anyone who specifies, operates or maintains instrumentation for critical applications knows that tank gauging redundancy is one of the most effective methods of reliable level detection. In fact, the updated API RP 2350 standards recommend redundant sensors for Category III – or unattended – tanks. Ideally, redundant sensors will be of disparate technologies to avoid multiple or simultaneous failures due to an intrinsic behavior or “weakness” of a given technology.
For Category III tanks, the API 2350 recommendations state tanks must be equipped with an automated tank gauging system (ATGS) consisting of a level sensor and independent High-High sensor. The output of both instruments must be transmitted to a control center in real time. The level sensor will be continuous. The High-High level sensor may be continuous or point. Sensors with self-diagnostics are preferred.
Examples of disparate technologies that work well together on a Category III tank include a displacer switch coupled with a non-contact radar transmitter, or an ultrasonic switch combined with a guided wave radar transmitter. Your specific tank and roof configuration will determine the most effective technology combination to use.