Apogee SI-421 Owner's Manual - Page 18

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TROUBLESHOOTING AND CUSTOMER SUPPORT

Independent Verification of Functionality:

The simplest way to check sensor functionality is the aM2! command. This command returns detector

temperature and detector voltage output. Detector temperature should read very near room

temperature. When the aperature of the sensor is covered with aluminum foil, the voltage output should

read very near 0 mV.

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

should be near 1.1 mA when the sensor is not communicating and spike to approximately 6 mA when the

sensor is communicating. Any current drain greater than 6 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 SDI-12 functionality that includes the M or C command.

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

webpage at http://www.apogeeinstruments.com/content/Infrared-Radiometer-Digital.CR1.

Modifying Cable Length:

SDI-12 protocol limits cable length to 60 meters. For multiple sensors connected to the same data line,

the maximum is 600 meters of total cable (e.g., ten sensors with 60 meters of cable per sensor). See

Apogee webpage for details on how to extend sensor cable length

(http://www.apogeeinstruments.com/how-to-make-a-weatherproof-cable-splice/).

Signal Interference:

Due to the small voltage signals from the detector, care should be taken to provide appropriate

grounding for the sensor and cable shield wire, in order to minimize the influence of electromagnetic

interference (EMI). In instances where SI-100 series radiometers are being used in close proximity to

communications (near an antenna or antenna wiring), it may be necessary to alternate the data recording

and data transmitting functions (i.e., measurements should not be made when data are being transmitted

wirelessly). If EMI is suspected, place a tinfoil cap over the front of the sensor and monitor the signal

voltage from the detector. The signal voltage should remain stable at (or very near) zero.