I can only tell for my SM2000 #348, hoping that a 54 has a similar solution. WEMA S2-1170F It is basically a resistor divider with reed relays. The float contains a magnet closing one of the reed relays.
I found that the inaccuracy was due to the natural 24V battery voltage changes and the bleeder resistor. So I put a 12V voltage regulator in series and changed the bleeder resistor value so that there is always a constant 12V on top of the resistor divider. Then checked its calibration ( by tank volume/ float position comparison) It is better now.
Hope this helps you,
Stefan Jeukendrup sv Malaka Queen SM2k #348 @ Montenegro
