Campbell 237, Product Manual

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237 Leaf Wetness Sensor
9
9. Troubleshooting
TABLE 9-1 lists the causes of unusual resistance readings.
TABLE 9-1. Symptom/Causes
Resistive Value
Causes IEEE4 FP2
INF, ≥ 99999,
≤ -99999
INF, ±7999
The 1 k Ω bridge resistor holds the input channel at 0 mV when the
sensor is completely dry. However, the measurement may intermittently
deviate from zero slightly, but still be within the resolution
specifications of the datalogger. When this occurs, Rs = either a very
large or a very small number.
NAN, -100,
-INF
NAN
NAN can indicate that no sensor is connected or a cable has been
cleanly cut if the mV200C , mV25C , or mV50C range code was used for
the BrHalf instruction.
Another cause of these outputs is a highly conductive state (> 25 mV)
that occurs if the sensor is very wet with very ionic water.
< 0
If the measured voltage exceeds 24.75 mV, but does not exceed the
input voltage range, the result of the bridge equation becomes negative.
10. References
1 Gillespie, T.J. and Kidd, G.E. 1978. Sensing duration of leaf moisture
retention using electrical impedance grids. Can. J. Plant Sci. 58:179-187.
2 East, David (Ohio State University). 1994. Field Testing of Phone Accessible
Multi-Channel Datalogger for Tomato IPM Programs. Unpublished.
The citation of researcher does not imply the endorsement of
Campbell Scientific products by any researcher or institution.
NOTE