Apogee S2-442 Manual del usuario - Página 15

Navegue en línea o descargue pdf Manual del usuario para Accesorios Apogee S2-442. Apogee S2-442 19 páginas. Par-far sensor

MAINTENANCE AND RECALIBRATION

Blocking of the optical path between the target and detector can cause low readings. Occasionally, accumulated

materials on the diffuser of the sensor can block the optical path in three common ways:

1. Moisture or debris on the diffuser.

2. Dust during periods of low rainfall.

3. Salt deposit accumulation from evaporation of sea spray or sprinkler irrigation water.

Apogee Instruments sensors have a domed diffuser and housing for improved self-cleaning from rainfall, but active

cleaning may be necessary. Dust or organic deposits are best removed using water, or window cleaner, and a soft

cloth or cotton swab. Salt deposits should be dissolved with vinegar and removed with a cloth or cotton swab. Salt

deposits cannot be removed with solvents such as alcohol or acetone. Use only gentle pressure when cleaning

the diffuser with a cotton swab or soft cloth, to avoid scratching the outer surface. The solvent should be allowed

to do the cleaning, not mechanical force. Never use an abrasive material or abrasive cleaner on the diffuser.

Although Apogee sensors are very stable, nominal calibration drift is normal for all research-grade sensors. To

ensure maximum accuracy, recalibration every two years is recommended. Longer time periods between

recalibration may be warranted depending on tolerances. See the Apogee webpage for details regarding return of

sensors for recalibration (http://www.apogeeinstruments.com/tech-support-recalibration-repairs/).

To determine if a specific sensor needs recalibration, the Clear Sky Calculator (www.clearskycalculator.com)

website and/or smartphone app can be used to indicate PPFD incident on a horizontal surface at any time of day at

any location in the world. It is most accurate when used near solar noon in spring and summer months, where

accuracy over multiple clear and unpolluted days is estimated to be ± 4 % in all climates and locations around the

world. For best accuracy, the sky must be completely clear, as reflected radiation from clouds causes incoming

radiation to increase above the value predicted by the clear sky calculator. Measured PPFD can exceed PPFD

predicted by the Clear Sky Calculator due to reflection from thin, high clouds and edges of clouds, which enhances

incident PPFD. The influence of high clouds typically shows up as spikes above clear sky values, not a constant

offset greater than clear sky values.

To determine recalibration need, input site conditions into the calculator and compare PPFD measurements to

calculated PPFD for a clear sky. If sensor PPFD measurements over multiple days near solar noon are consistently

different than calculated PPFD (by more than 6 %), the sensor should be cleaned and re-leveled. If measurements

are still different after a second test, email

possible return of sensor(s).

The Clear Sky Calculator does not calculate far-red photon flux density, but it can be approximated from PPFD

returned from the calculator. The ratio of far-red photon flux density to PPFD on clear days near solar noon is

typically within the range 0.20 to 0.22.

to discuss test results and