Campbell Scientific CS506 Fuel Moisture Sensor - Manual (Page 11)

CS506 Fuel Moisture Sensor
5. Datalogger Programming
This section is for users who write their own datalogger programs. A
datalogger program to measure this sensor can be created using Campbell
Scientific’s Short Cut Program Builder software. You do not need to read this
section to use Short Cut.
The CS506 has a built in enable circuit. When voltage on the enable lead is
less than 1 VDC, the sensor is off. When a voltage greater than 4 VDC,
commonly 5 VDC, is applied to the enable lead, the sensor is on. The output
signal is a
±0.7 volt square wave. The CRBasic instruction PeriodAvg is used
with the CR800-series, CR1000, and CR3000 dataloggers to measure the
period of the output signal in microseconds on a single-ended analog input
channel. For Edlog dataloggers, instruction P27 Period Average may be used
with the CR500, CR510, CR10, CR10X, and CR23X dataloggers. The CS506
is not compatible with 21X, CR7, or CR200-series dataloggers.
Since fuel moisture does not change very rapidly, the sensor is typically
measured only once per hour.
After the period of the output signal in microseconds is measured it is
converted to percent water content using one of two equations:
θ(τ ≤ 17.7) = 7.6298τ -130.0904
θ(τ > 17.7) = 0.0406τ 2 + 3.7685 τ - 73.7974
where θ is the percent of water by weight in the fuel moisture stick and τ is
period average in microseconds.
There is a slight disconnect in the two equations at 17.7 μs where the linear
equation gives a water content of 4.98% while the quadratic equation gives
5.68%. A sudden small increase or decrease in the measured water content
near 5% is to be expected as the datalogger changes from one equation to the
other.
TABLE 5-1. Wiring for Example Programs
Color CR1000 CR10X
Red 12 V 12 V
Black G G
Green SE1 SE1
Orange C1 C1
Clear G
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