Answer
Your Hardy Instrument can power at least four 350 ohm load cells and, depending on the model, up to eight load cells. If you connect more load cells than your Hardy Instrument can handle, the excitation voltage will drop and your instrument will not boot up. If you want to connect additional load cells to your Hardy Instrument, the excitation voltage should be supplied by an external power supply. The HI 1771WS, HI 2160 and the HI 2151/20WC use 10 volts (+5v and -5v) for excitation and the other Hardy units use 5 volts (+5v & gnd) for excitation. If you use an external power supply make sure it supplies the same voltage level as your Hardy Instrument.
Attached is a Tech Note Schematic that shows how to connect an external power supply to a Hardy Instrument.
