When should I use jumpers between the excitation and sense lines?

When do I need to remove or leave the jumpers between exc+ sen+ and exc- sen- that come standard on all new Hardy weight controller load cell connectors? When do I need to remove the jumpers from the connector and place them in the Junction Box connector?

On the Hardy units, the reason for having sense lines is to provide a way for the controller to calculate the excitation voltage loss between the weight controller and the summing junction box over the length of cable.

Utilizing the sense lines is required for all applications using C2 calibration to maximize your system accuracy. 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 wires between the controller and the junction box. If sense wires are not used, then the jumpers need to remain on the load cell connector. There is no need to use the jumpers in the junction box connector, as the excitation and sense lines should be tied together on the junction box terminal strip. Connect the EXC+ to SENSE+ and EXC- to SENSE-.

How the sense function is used:

Performing a Hard calibration:
Uses the actual actual excitation voltage after loss over the length of the cable, received during hard calibration. The sense line will re-establish the reference range to utilize the full register of the A/D converter.

Performing a C2® calibration:
If the sense lines are not used to measure the actual excitation voltage at the junction box, an error will be introduced. The error will be equal to the percentage of excitation voltage lost between the instrument and the junction box. If the excitation voltage at the back of the instrument was 5 volts and the excitation voltage at the junction box was 4.9 volts, 0.1 volts was lost due to cable resistance. This loss will cause a linear error of 0.98% (4.9 divided by 5) of applied load in all weight readings. This error is introduced because the programmed millivolt per volt (mV/V) data of the load point is multiplied by the voltage between the sense lines to compute the calibration curve of the load point. This is true with long cables and intrinsic barriers.

Note: There is not a case where you would want to install jumpers in the summing junction box. The diagram of the Integrated Technician (IT) summing junction box suggests there is a jumper between C2 + and C2- if no C2® is used. This is not true and adding a jumper from +C2 and -C2 will damage the controller if left on for an extended time.