Question
I am trying to install a Hardy Instrument and there are 9 wires:
2 for signal, 2 for excitation, 2 for C2®, 2 for sense and a shield wire.
What are the 2 sense wires for?
Answer
The extra sense wires on your Hardy Instrument help maintain the C2® calibration reference level to adjust for excitation voltage, cable resistance and voltage loss from the C2 cable cable running from the summing junction box. In short, the sense wires increase the accuracy of your weighing system by measuring the resistance of your home run cable and factoring that value into your calibration. The sense lines form a loop from the summing junction box connection back to the weight controller. If the cable loss is included in the C2® calibration your system accuracy should improve. To utilize the C2® function you should connect the +Sense and +Excitation wires together on the +EXC junction box TB9 terminal strip. Also connect the -Sense and -Excitation wires together on the -EXC junction box TB9 terminal strip. The signal returned from the load cells is very small and even slight excitation voltage change results in a large weighing error.
NOTE: The length of the load cell cables are included in the C2® calibration calculations and should never be cut! See related answer below.
At the factory the weight controllers have two jumper wires installed on the load cell connector. These jumpers are connected from EXC+ to SENSE+ and EXC- to SENSE-. Remove these jumpers and install the sense lines to utilize the sense functionality. These are installed for those installations with only 4 wire home runs and no C2 capable load cells.
