User Manual

Red: Power In (4.5-24 V DC)
Black: SDI-12 Data Line
Clear: Ground (shield wire)
Black: Ground
Red: Power In (5.5-24 V DC)
White: SDI-12 Data Line
Clear: Shield/Ground
OPERATION AND MEASUREMENT
The SQ-421 quantum sensor has a SDI-12 output, where shortwave radiation is returned in digital format.
Measurement of SQ-421 quantum sensors requires a measurement device with SDI-12 functionality that includes
the M or C command.
VERY IMPORTANT: Apogee changed the wiring colors of all our bare-lead sensors in March 2018 in conjunction
with the release of inline cable connectors on some sensors. To ensure proper connection to your data device,
please note your serial number or if your sensor has a stainless-steel connector 30 cm from the sensor head then
use the appropriate wiring configuration listed below. With the switch to connectors, we also changed to using
cables that only have 4 or 7 internal wires. To make our various sensors easier to connect to your device, we clip
off any unused wire colors at the end of the cable depending on the sensor. If you cut the cable or modify the
original pigtail, you may find wires inside that are not used with your particular sensor. In this case, please
disregard the extra wires and follow the color-coded wiring guide provided.
Wiring for SQ-421 Serial Numbers 2053 and above or with a cable connector
Wiring for SQ-421 Serial Numbers within the range 0-2052