National Instruments RMX-4120 User Manual

Also see for RMX-4120: Safety & installation instructions

Contents

© National Instruments | 1-19RMX Programmable Power Supplies User ManualLocal SensingBy factory default, RMX programmable power supplies are set to local sensing (the rear panelsensing connector is hard wired). The sensing point during local sensing is the output terminal.This method does not compensate for the voltage drop across the load cable, so use this methodwhen the load current is small or when you do not need to consider the load effect voltage.Figure 1-20. Local SensingRemote SensingRemote sensing is a feature that reduces the effect of voltage drops across load cablingresulting in a more accurate voltage being applied at the terminals of the load.Refer to Appendix A, Specifications for the maximum voltage drop each RMX power supply'sremote sense terminals can compensate for. Select a load cable that has sufficient currentcapacity to prevent the voltage drop in the load cable from exceeding the compensation voltage.Refer to the Load Cables section for more information about the cables.When using remote sensing, the output terminals compensate for the voltage drop across the loadcabling by increasing the output voltage above the programmed setpoint until the sense leadsdetect the programmed setpoint at the load itself. This requires the output terminals to generatea voltage that is greater than the programmed voltage level. If you are performing remote sensingwith the voltage close to the maximum output voltage of the power supply, the total output isstill limited by the maximum output voltage at the terminals of the power supply (105% of therated output voltage). If the signal doesn’t seem to be stable, an electrolytic capacitor may berequired at the sensing point (across the load).To minimize noise on the output signal, use twisted-pair wires or 2-core shielded wires. Connectthe ground of your shielded wire to the ground of the RMX programmable power supply or theload.+–+LS+S-LS-SOutput terminalChassis terminalSensing terminalRMXLoadUse twisted-pair wires for the load cables.Make the cables as short as possible.