Apogee Instruments S2-141 Gebruikershandleiding - Pagina 11

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OPERATION AND MEASUREMENT

The S2-442 PAR-FAR sensor has a Modbus output, where PPFD and far-red photon flux density are returned in

digital format. Measurement of S2-442 PAR-FAR sensors requires a measurement device with a Modbus interface

that supports the Read Holding Registers (0x03) function.

Wiring

The Green wire should be connected to Ground to enable RS-485 communication, or it should be connected to 12

V power for RS-232 communication. Text for the White and Blue wires above refers to the port that the wires

should be connected to.

Sensor Calibration

All Apogee Modbus PAR-FAR sensors model (S2-442) have sensor-specific calibration coefficients determined

during the custom calibration process. Coefficients are programmed into the sensors at the factory.

Modbus Interface

The following is a brief explanation of the Modbus protocol instructions used in Apogee S2-442 PAR-FAR sensors.

For questions on the implementation of this protocol, please refer to the official serial line implementation of the

Modbus protocol:

http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf

Modbus protocol specification:

Further information can be found at:

Overview

The primary idea of the Modbus interface is that each sensor exists at an address and appears as a table of values.

These values are called Registers. Each value in the table has an associated index, and that index is used to identify

which value in the table is being accessed.

Sensor addresses

Each sensor is given an address from 1 to 247. Apogee sensors are shipped with a default address of 1. If using

multiple sensors on the same Modbus line, the sensor's address will have to be changed by writing the Slave

Address register.

http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf

http://www.modbus.org/specs.php

White: RS-232 RX / RS-485 Positive

Blue: RS-232 TX / RS-485 Negative

Green: Select (Switch between RS-232 and RS-485)

Black: Ground

Red: Power +12 V

(2006) and the general

(2012).