CS120A and CS125 Visibility and Present Weather Sensors
31
In accordance with WMO requirements the sensor produces
visibility measurement that are either one or ten minute rolling
averages that are updated at the chosen output interval or when the
sensor is polled. Those averages are not direct averages of MOR
measurements but are averages of extinction coefficient and that
average is then used to calculate the MOR for that period. As the
relationship between extinction coefficient and MOR is not linear
it is possible to see quite rapid changes in MOR that might not be
expected if the result was a rolling average of MOR. Please
consider this, especially when testing the sensor with artificial
obscurants or using the calibration disc.
User alarms
ID
Range
Definition
1
0-1
Visibility either less or greater than a user specified threshold
2
0-1
Visibility either less or greater than a user specified threshold
Table 11-2. Summary of system alarms and descriptions
System alarms break down
Alarm
Range
Severity
(2)
Definition
Emitter failure
(emitter hoods
main LED
output power
level)
0-2
0
3
3
0 = Everything is within normal parameters
1 = Light output level too low
2 = Light output level too high
Emitter lens
dirty
0-3
0
3
1
2
0 = OK. The reported attenuation is below 10%
1 = Reported window signal value is out of range (>30%)
Possible sensor fault or hood could be blocked
2 = Slight dirt build up (10% signal attenuation or higher)
3 = High level of dirt build up (>20%)
Emitter
temperature
0-3
0
1
1
3
0 = Temperature is within operating conditions
1 = Too low. Less than -40°C
2 = Too high. Over 80°C
3 = No sensor detected or below -54°C
Detector lens
dirty
0-3
0
3
1
2
0 = OK. The reported attenuation is below 10%
1 = Reported window signal value is out of range (>30%)
Possible sensor fault or hood could be blocked
2 = Slight dirt build up (10% signal attenuation or higher)
3 = High level of dirt build up (>20%)
Detector
temperature
0-3
0
1
1
2
0 = Temperature is within operating conditions
1 = Too low. Less than -40°C
2 = Too high. Over 80°C
3 = No sensor detected or below -54°C
Detector DC
saturation
level (amount
of background
light seen by
the detector
hood)
0-1
0
2
0 = Within limits
1 = Saturated. The sensor may not be able to perform visibility
readings in some circumstances. Possibly due to high level of
reflections into the detector.
NOTE
