Vaisala HMDW110 Serie Guide Rapide page 13

Wiring HMDW110 with RDP100
You must always connect the humidity measurement current loop (HUM,
terminals 5 and 6) to power the transmitter. Connecting the temperature
measurement current loop (terminals 7 and 8) is optional.
Connect the RDP100 Remote Display Panel using terminals 1 ... 4. The
HMDW110 series transmitter provides both power and data to the RDP100.
When using the RDP100 with HMDW110 series transmitters,
do not connect the Extpwr jumper to the RDP100 component
board.
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