This guide explains how to test your food and bbq probes for accuracy and some common symptoms.
- Most BBQ probes use thermistor based sensors, which provide a non-linear decrease to electrical resistance as temperature increases. For a *in depth* walkthrough of the science, checkout the The Engineering Mindset article.
- Probes are made differently between vendors and products - ie generic third party probes will not work. Thermistor probes are rated on a base resistance at room temperature (25C) and companies use a range of base ratings, we chose 1M Ohm as it provides better granularity in temperature readings across the key BBQ temperature range (100-400F), whereas low resistance probes designed for weather and traditional cooking (0F to 200F) lose that granularity. On top of that, different manufacturers use different non linear response curves.
- The non-liner response means if you "calibrate" a BBQ probe in an ice bath you actually don't know if it's anywhere near accurate at high BBQ ambient temperatures. You've only validated that it's accurate at freezing!
- Despite their rugged appearance, probes are quite fragile. The thermistor sensor is typically a glass coated bead of metallic oxide or ceramic. This means they can easily break if you drop them on hard ground (ie while untangling a mess of cables) or knock it into the side of the smoker. If you have a probe reading above 400F in the kitchen you know it's broken.
- "Calibrating" a probe with a saucepan boiling water is dangerous to you and the probe. It's hard to actually get true 100C, you can burn yourself, and the probe may get broken bouncing around the saucepan in rolling boiling water. There is a much easier and safer way.
To test probes for accuracy and/or issues, we recommend using a cup of hot water and all the probes plugged into your Smartfire.
- Warm up a cup with hot tap water, fill it halfway as we don't want the water past the cable/probe join on the shorter pit probe(s)
- Place all your probes into the cup of water, with the Smartfire active
- Check the status in the app
- If the probes are jumping in temperature try a different power supply, a laptop usb port is ideal
- Leave it running for 30-45 minutes
- What you're looking for is the probes to be agreeing with each other's readings within 4F and to be stable. With multiple Smartfire probes agreeing you know there are no hardware issues with the probe or Smartfire.
- You can always compare the current reading during the test to a quality instant read thermometer. With multiple probes from multiple systems matching you can bet the house that both systems are calibrated and accurate within a degree.
- If at any stage it appears there are issues, take a screenshot of the main status screen. Also take a screenshot of the detailed graph screen at the end of your test.
The most common one is 'everything is ok and the hood dial must be crazy', but here are some others to look out for.
- Erratic bumps in a probe's reading. If its jumping around every few seconds or minutes try another power supply. A laptop USB port is the ideal source of stable power.
- Consistently reading a narrow band of temperature well above 400F / 200C. The probe is likely broken, if it's reading above 500F it's certain. The thermistor sensor block is fragile (glass and ceramic) and hates being dropped on hard ground or hit into the side of a smoker.
- Reading a hundred or so degrees above the other probes, but varying during the test process as the water cools: likely the probe has moisture inside it. Leave it somewhere sunny and dry for a few days then test again.