A beeping sound rouses you at 1 AM, and looking out of the tent you see it's finally cleared off. You pop the tarp off your telescope, line up a shot, get the autoguider running, and start the exposure series going. You're still pretty tired though, so you head back into the tent, comfortable in the knowledge that the Boltwood Portable Cloud Sensor will wake you up if the conditions deteriorate again.
The Portable Cloud Sensor is designed to alert you when the cloud conditions change. It consists of a sensor head and a control box, connected by a cable. The sensor head is placed outside, pointing up at an unobstructed sky. The control box can be conveniently located inside a tent or building, as needed. The control box includes batteries that will power the unit for over 100 hours, plus an alarm beeper, a headphone jack for "silent" alarms, and simple user controls.
The Portable Cloud Sensor measures the amount of cloud cover by comparing the temperature of the sky to the ambient ground level temperature. The sky temperature is determined by measuring the amount of radiation in the 8 to 14 micron infrared band. A large difference indicates clear skies, whereas a small difference indicates dense, low-level clouds. This allows the sensor to continuously monitor the clarity of the skies, and to alert the user when conditions change.
A built-in daylight sensor is also included. When the sensor is set to detect "Clear & Dark" conditions, it will alarm for clear skies unless the sun comes up first, in which case it lets you sleep in. When the sensor is set to detect "Cloudy or Light" conditions, it will alert you when clouds roll in or dawn approaches, so you can protect your telescope against the elements (including the sun!).
Although the Portable Cloud Sensor uses the same cloud detection technology as it's big cousin, the Boltwood Cloud Sensor II, it is not designed for permanent installations. It does not detect rain/moisture, wind, or humidity. The sensor is gently heated to prevent dew or frost, but it does not have the power to clear itself after a rain shower; it must be wiped off. It cannot connect to a computer or trigger an observatory dome closure. For permanent installations please use the Boltwood Cloud Sensor II.
The sensor head, measuring only 1-1/2" in diameter by 5" long, is shown here in a typical temporary installation - taped to a stick. The cloud-sensing thermopile and daylight sensor are visible at top.
The control box, shown magnified above, can be conveniently located next to your pillow while you sleep. The simple user controls let you set the cloudy/clear threshold, set it to alarm for clear or cloudy conditions, and turn it on/off. On the side are two jacks; one for the sensor cable and one for optional headphones (not included).