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Fuel and Water Gauge Retrofit
Standard fuel and water level gauges 
rely on a resistive sender operating at either 240 to 33 ohms - or - 10 to 180 ohms.  These senders, mounted at the top of the tank use a float and a series of micro-switches and resistors to provide a resistance proportional to the tank level.    

Engine management systems rely on the same sender configuration to provide fuel tank levels to the engine's power control module.

While adequate to monitor a fluid's level, resistive senders have two inherent weaknesses - first, they are mechanical devices and therefore subject to mechanical failure and second, they provide no means to calibrate their signal to account for the geometry of the tank, and therefore cannot provide the tank's actual volume to either a gauge or EMS. 

SmartSwitch has addressed both of these shortcomings with their PR-100 retrofit for standard fuel/water gauges and the PR-200 retrofit for engine management systems and its associated gauges/displays 

In both of these retrofits the standard resistive sender is replaced with highly accurate and reliable solid-state pressure sender to measure tank level.  This is a straightforward replacement using the same mounting holes as the resistive sender. 

The PR-100/200 unit accepts the pressure signal and converts it to the 240/33 or 10/180 ohms signal required by the gauge or EMS.  

In addition, it allows either 2 or 5 point calibration, based on the tank's geometry thereby providing actual tank volume, to the gauge or EMS. 
Demo of the PR-100/200 Retrofit
  • Enhanced Reliability…  Replaces a mechanical sending unit with a more reliable a industrial-quality, solid-state pressure sensor
  • Accuracy….  Can measure levels to within 1/10 inch
  • True tank readings….  A fully calibrated signal gives actual readings of fuel or water levels – no more guesswork on how much is actually remaining in the tank
  • Ease of installation… New pressure sender installs in same footprint as old resistive sender – only 7 wires to connect to PR-100/200 terminals – uses existing gauge wiring – no pulling of new wires
  • Ease of startup… Calibration can be completed prior to any work on the vessel minimizing on-board labor – system will be operational upon completion of physical installation and application of power
Advantages of the SmartSwitch PR-100/200 Level Gauge Retrofit 

It is common for vessels of all sizes to have tanks with irregular cross-section.  In those cases, the resistive signal available to the gauge or engine management system will not be representative of the actual volume of fuel or water in the tank.