Apogee SQ-514 Instrukcja obsługi - Strona 18

Przeglądaj online lub pobierz pdf Instrukcja obsługi dla Akcesoria Apogee SQ-514. Apogee SQ-514 20 stron. Quantum sensor

Drukuj stronę

TROUBLESHOOTING AND CUSTOMER SUPPORT

Independent Verification of Functionality

Apogee SQ-514 series quantum sensors provide a 4-20 mA output that is proportional to incident PPFD. A quick

and easy check of sensor functionality can be determined using a DC power supply and an ammeter. Power the

sensor with a DC voltage by connecting the positive voltage signal to the red wire from the sensor and the negative

(or common) to the black wire from the sensor. Use the ammeter to measure across the white wire (signal output)

and green wire (signal ground). 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 4 mA.

Compatible Measurement Devices (Dataloggers/Controllers/Meters)

-2

-1

SQ-514 series quantum sensors are calibrated with a standard calibration factor of 250.0 µmol m

per mA,

-2

-1

yielding a sensitivity of 0.004 mA per µmol m

. Thus, a compatible measurement device (e.g., datalogger or

-2

-1

controller) should have resolution of at least 0.004 mA in order to provide PPFD resolution of 1 µmol m

The 4-20 mA circuit design allows the output to drive a resistive load (R

) to within 2 volts of the supply voltage to

the sensor (V

), at 20 mA (0.02 A). The equation to calculate resistive load is R

= [V

– 2 V] / 0.02 A. For example, a

sensor with a supply voltage of 12 V DC can drive a maximum load of 500 Ω (R

= [12 V – 2 V] / 0.02 A = 500 Ω). The

output voltage from the sensor is calculated by adding the wire resistance to the input resistance of the data

collection system, and then multiplying by 0.02 A.

Cable Length

Shortening or splicing on additional cable in the field is generally not a problem for the current output of the SQ-

514. However, adding cable will result in a greater resistive load, which should be taken into consideration when

determining the maximum resistive load that the sensor will drive (see section above on Compatible Measurement

Devices). 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/).

Unit Conversion Charts

-2

-1

Apogee SQ-500 series quantum sensors are calibrated to measure PPFD in units of µmol m

. Units other than

photon flux density (e.g., energy flux density, illuminance) may be required for certain applications. It is possible to

convert PPFD from a quantum sensor to other units, but it requires spectral output of the radiation source of

interest. Conversion factors for common radiation sources can be found in the Knowledge Base on the Apogee

website (http://www.apogeeinstruments.com/knowledge-base/; scroll down to Quantum Sensors section). A

spreadsheet to convert PPFD to energy flux density or illuminance is also provided in the Knowledge Base on the

Apogee website (http://www.apogeeinstruments.com/content/PPFD-to-Illuminance-Calculator.xls).