16
TROUBLESHOOTING AND CUSTOMER SUPPORT
Independent Verification of Functionality
The radiation detector in Apogee SL-510 and SL-610 pyrgeometers is a self-powered device that outputs a voltage
signal proportional to the radiation balance between the detector and target surface. A quick and easy check of
detector functionality can be accomplished using a voltmeter with microvolt (µV) resolution. Connect the positive
lead of the voltmeter to the white wire from the sensor and the negative lead (or common) to the black wire from
the sensor. Direct the sensor toward a surface with a temperature significantly different than the detector. The
voltage signal will be negative if the surface is colder than the detector and positive if the surface is warmer than
the detector. Placing a piece of tinfoil in front of the sensor should force sensor voltage signal to zero.
The thermistor inside SL-510 and SL-610 pyrgeometers yields a resistance proportional to temperature. A quick
and easy check of thermistor functionality can be accomplished with an ohmmeter. Connect the lead wires of the
ohmmeter to the blue and green wires from the sensor. The resistance should read 30 kΩ at 25 C. If the sensor
temperature is less than 25 C, the resistance will be higher. If the sensor temperature is greater than 25 C, the
resistance will be lower. Connect the lead wires of the ohmmeter to the red and green wires from the sensor. The
resistance should read 24.9 kΩ, and should not vary. Connect the lead wires of the ohmmeter to the red and blue
wires from the sensor. The resistance should be the sum of the resistances measured across the blue and green
wires, and red and green wires (e.g., 30 kΩ plus 24.9 kΩ at 25 C).
Compatible Measurement Devices (Dataloggers/Controllers/Meters)
Apogee SL-510 and SL-610 pyrgeometers have sensitivities in the microvolt range, approximately 0.11 mV per W
m
-2
difference between target and detector. Thus, a compatible measurement device (e.g., datalogger or
controller) should have resolution of at least 0.11 mV to produce longwave radiation resolution of 1 W m
-2
.
Measurement of detector temperature from the internal thermistor requires an input excitation voltage, where
2500 mV is recommended. A compatible measurement device should have the capability to supply the necessary
voltage.
An example datalogger program for Campbell Scientific dataloggers can be found on the Apogee webpage at
http://www.apogeeinstruments.com/content/Thermopile-Pyrgeometer-Unamplified.CR1
Modifying 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 measurement device is 10 MΩ or higher, there is negligible effect on the radiometer calibration,
even after adding up to 50 m of cable. Apogee SL-510 and SL-610 pyrgeometers use shielded, twisted pair cable,
which minimizes electromagnetic interference. This is particularly important for long lead lengths in
electromagnetically noisy environments. 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 SL-510 and SL-610 series pyrgeometers 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.
Содержание SL-510
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