People that compare the Mopeka Phone App with the RV Whisper display often wonder how the values can be different from each other. It’s actually pretty straightforward why (to me anyway), but it takes a bit of explaining to understand why.
Each Mopeka sensor broadcasts the liquid height every few seconds from its Bluetooth radio transmitter. The liquid height is the only value that gets transmitted. The %Full calculation is up to the Mopeka Phone App and RV Whisper to do independently. RV Whisper currently calculates the %Full values for only 20lb and 30lb propane tanks which are most commonly used on travel trailers and fifth wheel trailers. These are the “Propane20-” and “Propane30-” sensor types. If you have a different size tank, you should focus on the “Liquid Height in Inches” measurement for your Propane tank.
While the Mopeka Phone App only shows you the most recent measurement that it sees over the Bluetooth radio, The RV Whisper Monitor Station sees the same liquid height measurements from the Mopeka sensors, but RV Whisper only logs the data every 300 seconds (every 5 minutes). So when you compare the two apps, you are almost always comparing sensor measurements from two different times – (data from sometime during the last 5 minutes in RV Whisper vs. data from just a few seconds ago in the Mopeka phone app). You should not assume the “Liquid Height in Inches” that the Mopeka sensor reports never changes except when you use propane.
The Mopeka sensor liquid height value that gets transmitted can change every few seconds as the physics of the measurements can be affected by several things such as motion, poor positioning of the tank sensor, dirty tank bottom and an off-level tank. Even slight motion of the tanks causes the liquid to move a little bit which causes ultrasonic wave reflections that change the results a bit. Walking around in the RV usually creates enough movement to affect the tank readings, and it can take several minutes for the liquid motion to stop. Also, as the tank cools and heats, the liquid expands and contracts significantly. And of course, if the propane tank bottom is dirty, or the sensor is not pressed cleanly against the tank bottom, or the sensor is not level, or the tank is not level, the measurements can vary even more.
The Mopek phone app displays a “quality” metric. If the “Quality” metric is low, that means the sensor is not making good contact, or the tank bottom is not clean, or the sensor is not horizontal, or the tank (and/or the RV) are not level. This usually means the tank level reported every few seconds is changing a lot or a little.
Hopefully, this provides some insight into why the Mopeka Phone app and RV Whisper data can be different by a few percent.