I am very interested in trying a load cell to monitor the level of propane in a 300 lb cylinder, but that's a project for a different day. I am curious though, if folks have real experience with a permanently installed load cell under a heavy load. Without the ability to zero it out once in a while, does it still provide usable, accurate weight readings month after month, year after year? In weather?
Commercial industrial load cells are very rugged and reliable unless subjected to large mechanical loads well above their maximum level. We used a lot of them in the refinery I worked at and rarely had problems with them. The best method to handle short term calibration factor is to have a 'software tare' factor in your sketch that you have the operator selects after placing a known empty cylinder on the scale. This will give your sketch a 'zero offset' factor you can subtract from the raw A/D measurement. Stability of your measurement over time will be more a factor of your external circuitry used to interface the load cell to the arduino. A load cell is a low level (millivolts) precision sensor and really should be used with an external A/D converter chip that has true differential input pins, internal voltage reference, and programmable gain, the added expense is justified in most cases and there are many such chips to choose from.
Lefty