Apogee S2-131-SS Manuel du propriétaire - Page 13

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TROUBLESHOOTING AND CUSTOMER SUPPORT

Independent Verification of Functionality

Apogee model S2-131 red - far-red sensors are self-powered devices and output two voltages, proportional to red

and far-red photon flux density (PFD), respectively. A quick and easy check of sensor functionality can be

determined using a voltmeter with millivolt resolution. To verify the red sensor, connect the positive lead wire

from the voltmeter to the yellow wire from the sensor and the negative (or common) lead wire from the voltmeter

to the blue wire from the sensor. Direct the sensor head toward a light source and verify the sensor provides a

signal. Increase and decrease the distance from the sensor head to the light source to verify that the signal

changes proportionally (decreasing signal with increasing distance and increasing signal with decreasing distance).

Blocking all radiation from the sensor should force the sensor signal to zero. To verify the far-red sensor, follow the

same procedure, but connect the positive lead wire from the voltmeter to the white wire from the sensor and the

negative lead wire from the voltmeter to the black wire from the sensor.

Compatible Measurement Devices (Dataloggers/Controllers/Meters)

S2-131 series red - far-red sensors are calibrated with a calibration factors of approximately 12 mol m

-2

-1

per mV

(typical value, variable from sensor to sensor), yielding sensitivities of 0.083 mV per mol m

-2

-1

for the red and

far-red sensors. Thus, a compatible measurement device (e.g., datalogger or controller) should have resolution of

at least 0.08 mV in order to provide red and far-red photon flux density resolution of 1 mol m

-2

-1

and 0.008 mV

in order to provide red and far-red photon flux density resolution of 0.1 mol m

-2

-1

An example datalogger program for Campbell Scientific dataloggers can be found on the Apogee webpage

(https://www.apogeeinstruments.com/content/Red-Far-Red-Sensor.CR1).

Cable Length

When the sensor is connected to a measurement device with high input impedance, sensor output signals are not

changed by shortening the cable or splicing on additional cable in the field. Tests have shown that if the input

impedance of the measurements device is greater than 1 mega-ohm there is negligible effect on the calibration,

even after adding up to 100 m of cable. All Apogee sensors use shielded, twisted pair cable to minimize

electromagnetic interference. For best measurements, 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.

Modifying Cable Length

See Apogee webpage for details on how to extend sensor cable length

(http://www.apogeeinstruments.com/how-

to-make-a-weatherproof-cable-splice/).