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OPERATION AND MEASUREMENT

The SQ-627 Extended Range PFD sensor has a SDI-12 output, where photosynthetically active radiation is returned

in digital format. Measurement of SQ-627 Extended Range PFD sensors requires a measurement device with SDI-

12 functionality that includes the M or C command.

Wiring

Sensor Calibration

All Apogee SDI-12 Extended Range PFD sensor models (SQ-600 series) have sensor-specific calibration coefficients

determined during the custom calibration process. Coefficients are programmed into the microcontrollers at the

factory.

SDI-12 Interface

The following is a brief explanation of the serial digital interface SDI-12 protocol instructions used in Apogee SQ-

627 Extended Range PFD sensors. For questions on the implementation of this protocol, please refer to the official

version of the SDI-12 protocol:

Overview

During normal communication, the data recorder sends a packet of data to the sensor that consists of an address

and a command. Then, the sensor sends a response. In the following descriptions, SDI-12 commands and

responses are enclosed in quotes. The SDI-12 address and the command/response terminators are defined as

follows:

Sensors come from the factory with the address of "0" for use in single sensor systems. Addresses "1 to 9" and

"A to Z", or "a to z", can be used for additional sensors connected to the same SDI-12 bus.

"!" is the last character of a command instruction. In order to be compliant with SDI-12 protocol, all commands

must be terminated with a "!". SDI-12 language supports a variety of commands. Supported commands for the

Apogee Instruments SQ-627 Extended Range PFD sensors are listed in the following table ("a" is the sensor

address. The following ASCII Characters are valid addresses: "0-9" or "A-Z").

http://www.sdi-12.org/specification.php

White: Positive (signal from sensor)

Red: Input Power

Black: Ground (from sensor signal and output power)

Clear: Shield/Ground

(version 1.4, August 10, 2016).