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TROUBLESHOOTING AND CUSTOMER SUPPORT

Independent Verification of Functionality

If the sensor does not communicate with the datalogger, use an ammeter to check the current drain. It should be

near 37 mA when the sensor is powered. Any current drain significantly greater than approximately 37 mA

indicates a problem with power supply to the sensors, wiring of the sensor, or sensor electronics.

Compatible Measurement Devices (Dataloggers/Controllers/Meters)

Any datalogger or meter with RS-232/RS-485 that can read/write float or integer values.

An example datalogger program for Campbell Scientific dataloggers can be found at

https://www.apogeeinstruments.com/content/PAR-Far-Sensor-Modbus.CR1.

Cable Length

All Apogee sensors use shielded cable to minimize electromagnetic interference. For best communication, the

shield wire must be connected to an earth ground. This is particularly important when using the sensor with long

lead lengths in electromagnetically noisy environments.

RS-232 Cable Length

If using an RS-232 serial interface, the cable length from the sensor to the controller should be kept short, no

longer than 20 meters. For more information, see section 3.3.5 in this document:

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

RS-485 Cable Length

If using an RS-485 serial interface, longer cable lengths may be used. The trunk cable can be up to 1000 meters

long. The length of cable from the sensor to a tap on the trunk should be short, no more than 20 meters. For more

information, see section 3.4 in this document:

Troubleshooting Tips

•

Make sure to use the green wire to select between RS-232 and RS-485.

•

Make sure that the sensor is wired correctly (refer to wiring diagram).

•

Make sure the sensor is powered by a power supply with a sufficient output (e.g., 12 V).

•

Make sure to use the appropriate kind of variable when reading Modbus registers. Use a float variable for

float registers and an integer variable for integer registers.

•

Make sure the baudrate, stop bits, parity, byte order, and protocols match between the control program

and the sensor. Default values are:

Baudrate: 19200

Stop bits: 1

Parity: Even

Byte order: ABCD (Big-Endian/Most Significant Byte First)

Protocol: RS-232 or RS-485

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