Campbell Scientific PWS100 Present Weather Sensor - Manual (Page 99)

Section 8. Functional Description
8.8 Internal Monitoring
The PWS100 has a number of internal checks including temperature analysis
inside each head unit of the sensor, temperature check at the laser, dirty
window contamination checks and voltage monitoring (particularly for the
laser source). These can be selected for output with the weather data; see
Section 7.4 for details.
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