The external resistor control is activated using an external voltage control. To set it up, go to the CONFIG setting, select SIGNAL SOURCE, choose EXT in SELECT, and choose J1 in EXT SELECT. Then, divide the reference voltage between pin No. 21 and 25 of the J1 connector by a resistance and apply it to pin No. 23. The voltage divider ratio is determined by a resistor.
For example, if you connect a 5 kΩ resistor between pin No. 25 and 23, and another 5 kΩ resistor between pin No. 23 and 21, the voltage between pin No. 23 and 24 is 0 V, and the output is 0 V. If you connect a 2.5 kΩ resistor between pin No. 25 and 23, and a 7.5 kΩ resistor between pin No. 23 and 21, the voltage between pin No. 23 and 24 is 5.4 V, and the output is 19 V.
For the details, read the user’s manual – chapter of External Control, Parallel Operation, and Synchronization – Controlling DC Signals – Using External Resistance.
