Maple Digital Barometer with Probe and Relay (Auto Draw Off)

(5 customer reviews)


The Plymouth Sugarworks atmospheric pressure compensating temperature device with probe and relay was designed to reduce the effort of determining when maple sap has transformed into maple syrup. It is designed to automatically operate a draw-off valve. It is also handy when making maple cream and candy.

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The boiling point of water is often stated to be 212°F, though this is only true at 1 atmosphere of pressure, commonly referred to as sea level. Without weather, atmospheric pressure decreases as elevation increases. But we live in a world with weather, which means atmospheric pressure (even at sea level) changes throughout the day. For example, water will boil at 209.6°F with a pressure of 28.5 inHg. When the pressure rises to 29.25 inHg the boiling point increases to 210.9°F, a difference of 1.3°F. 1.3°F is the difference between 63.6% and 66.9% syrup.

This device measures barometric pressure every second to determine the boiling point of water, no matter the elevation or the weather. Simply connect the included USB C cable a power source (e.g. a phone charger, portable battery pack, or computer). The unit will automatically turn on and display the current barometric pressure (in inches of mercury, or inHg), the boiling point of water in Fahrenheit, and the boiling point of syrup at a density of 66.9%. The temperature probe will measure the current sap temperature and display how many degrees are left until the sap is at the proper temperature for 66.9% syrup. Once the temperature of the sap gets above the boiling point of water the device will estimate the Brix of the sap. When the sap reached the proper density a red light will illuminate and an alarm will beep five times. The alarm can be disable if desired. The until will also energize a relay that will close a circuit, energizing whatever is connected to the device (15 amp maximum). This will open the draw off valve. When the temperature drops below the temperature of syrup the relay deenergize, opening the circuit and closing the valve.

The included thermometer probe is highly accurate, though you can further calibrate the unit +/- 2.4°F to suit your setup. The waterproof temperature probe is made from stainless steel and can be scrubbed clean after use. An optional silicon sheathed cable is available that offers greater flexibility in cold weather and is rated to withstand temperatures up to 392°F.

These devices were designed and assembled in Plymouth, Connecticut. If you would like your device customized (e.g. to display in Celsius or a different Brix range, just let me know). Includes the digital barometer, a USB C power cable, temperature probe, and operating instructions.

A valve and power supply for the valve are not included. Many folks have reported good results with this motorized ball valve and power supply from Amazon.

A manual is available here: Maple Digital Barometer with Probe and Relay (Auto Draw Off).

Additional information

Weight 17 oz
Dimensions 8 × 8 × 3 in

5 reviews for Maple Digital Barometer with Probe and Relay (Auto Draw Off)

  1. Mike Cavanagh

    A great time saver! Thank you for the support getting me up and running.

  2. Jamesflink

    This really makes things easier. Simple to setup and use.

  3. Jean Leonard (verified owner)

    Had this last year but didn’t use the draw off till this season! Game changer for me! Great product! Great support!

  4. Shelly

    I love this tool, takes the guess work out of determining boiling point of water and temp for syrup. So glad I found it! I reached out to request a new instruction sheet because I had misplaced mine. I had a reply within a day with an electronic version. Thank you!

  5. Craig Nadjiwon

    I work for a 8000 tap company and this unit has been a game changer, we run alot of sap and this takes the guess work out of it. Draw offs are accurate, and quick. I’ll be buying more. Thank you very much, I really enjoy this technology.

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