How do I know if this sensor disc is compatible with my Boltwood Cloud Sensor II?
You must check the serial number on your Boltwood Cloud Sensor II unit. This replacement disc is only compatible with serial numbers 4000 and higher. It will not work with older units that have a serial number lower than 4000.
What does the Diffraction Limited Thermopile / Rain Sensor Disc do?
This part replaces the thermopile / rain sensor at the sky end of the Boltwood Cloud Sensor II head. The thermopile measures sky temperature for cloud detection, and the white wetness disk around it senses individual rain drops, a film of water, snow and ice. These readings drive the Clarity II alerts and the Cloud Sensor II's roof-close contact closure.
My observatory roof closed due to a false rain alert from my Boltwood Cloud Sensor II. Could this part fix that?
Possibly. The Cloud Sensor II manual notes that wetness readings can drift with humidity, dirt, aging and temperature, and that touching or coming near the sensor gives a rain or wet indication for about 1 minute. Rule out those causes and clean the sensor head first; if the fault remains, the disc may need replacing.
Is this replacement sensor disc difficult to install on my Boltwood Cloud Sensor II?
No, it is designed for customer installation. You can replace the disc in the field without needing to send the entire Boltwood Cloud Sensor II unit in for service, minimizing downtime for your observatory.
Why is the Diffraction Limited Rain Sensor Disc heated?
The sensor is actively heated for two reasons:
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Prevention: The sky end of the sensor head is normally heated to 8C (15F) or more above ambient to prevent dew or frost, because the thermopile cannot see through any form of water.
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Recovery: When the rain stops but the wetness sensor is still wet, the sensor head is heated to 60C (140F) until it is dry, returning the system to a "dry" state so you can resume observing.
Does the Diffraction Limited Rain Sensor Disc require maintenance?
The sensor itself is a solid-state component with no moving parts. However, for accurate readings, it's important to keep the sensor head free of dirt, leaves, bird droppings and snow, as an obstruction can cause false cloudy readings. The manual recommends cleaning the thermopile window gently, as you would an optical surface.
