Temperature readings vary stick vs laser

[breeves2245]

I have a stick and laser temperature probes. I they were giving me different readings so I took them to the local brew shop. We tested his stick probe, my stick probe and my laser in cold tap and hot tap. His stick read about 4° higher than my stick and my laser about 4-8° lower at cold tap. 76/72/68.

Hot tap his stick 122°, my stick 117°, my laser 110°. He then took a probe out of a boil pot. It read 112° at hot tap.

I got home and used ice water. Laser 31.5°, my stick 40°. But at temps approaching mash temps and up to boiling both stick and laser were with a couple of three degrees. Seems laser is more accurate at lower temps then the sticks.

 

[Dfitz]

A man who wears two watches seldom knows what time it is. If you need to verify your temp gauge I'd recommend using a gauge that is traceable to NIST standard. I keep a dial thermometer around just for this purpose. It doesn't really do much good if you have no calibration ability to the gauge you use but at least you'll know how far off you are at a given temp.

 

[LarMoeCur]

I've never been a fan of laser thermometers used for brewing. They are great for when your in a hurry and need a ball park figure. I've used them on race engines to see quickly see if I have a cylinder out. I've used them to check my kid for a fever. The hot not reading reading right stems from the laser hitting vapors as they rise from the hot liquid. It's very difficult to get a good refection off of the hot surface. I realized quickly that if I want to hit temps spot on I'd have to bite the bullet and buy a good thermometer. If you get one good one you can calibrate all the crappy ones to it. I recommend anything from Thermoworks. Not to pricey and highly recommended here.

 

[breeves2245]

Based on no actual data, I figured the stick thermometer would be more accurate. But when I got a 40° degree reading from ice water and the laser had 31.5°, that made me question the stick. I'll check out Thermoworks.

 

[TheMadKing]

I've never been a fan of laser thermometers used for brewing. They are great for when your in a hurry and need a ball park figure. I've used them on race engines to see quickly see if I have a cylinder out. I've used them to check my kid for a fever. The hot not reading reading right stems from the laser hitting vapors as they rise from the hot liquid. It's very difficult to get a good refection off of the hot surface. I realized quickly that if I want to hit temps spot on I'd have to bite the bullet and buy a good thermometer. If you get one good one you can calibrate all the crappy ones to it. I recommend anything from Thermoworks. Not to pricey and highly recommended here.

This

I use my laser to check keg temps in my kegerator, check wort temp during chilling, and to drive my dog nuts. That's about it!

 

[dyqik]

I've never been a fan of laser thermometers used for brewing. They are great for when your in a hurry and need a ball park figure. I've used them on race engines to see quickly see if I have a cylinder out. I've used them to check my kid for a fever. The hot not reading reading right stems from the laser hitting vapors as they rise from the hot liquid. It's very difficult to get a good refection off of the hot surface. I realized quickly that if I want to hit temps spot on I'd have to bite the bullet and buy a good thermometer. If you get one good one you can calibrate all the crappy ones to it. I recommend anything from Thermoworks. Not to pricey and highly recommended here.

You absolutely don't want a reflection off the surface to get a measurement with an IR thermometer (there's no laser involved in the measurement, it's just a laser pointer used to target the sensor). The IR thermometer detects the emission from an (assumed) black or gray* object, not the reflection of something.

In brewing, an IR thermometer can be confused by poor emissivity from the surface of the liquid, reflections in the liquid surface of the rest of the room, and by absorption in the air/vapor over a pot. If you use it on the outside of the pot, it may be confused by reflection in the pot itself. Most thermometers assume that the emissivity of the object it's being pointed at is >0.9, but that gets very hard to quantify when viewing through steam or at a reflective surface. E.g. See fig. 5 and the discussion around it at http://www.omega.com/temperature/Z/pdf/z059-062.pdf

Don't trust them in brewing. Use a trusted digital thermometer, preferably with a traceable calibration like the Thermoworks. CDN make some pretty good cheaper digital thermometers.

*meaning that the emissivity is constant with wavelength in the regime where the measurement is made.

 

[AZCoolerBrewer]

Finding and using a thermometer in brewing is a learning experience. I used the glass thermometer that came with my first brewing kit for about 8 batches until my water started boiling at 220 degrees. I then started using a meat thermometer since that's what I had laying around. After 2 batches water started boiling at 217 degrees. Bit the bullet and bought a thermoworks 3 foot long digital thermometer and am having to get used to the accuracy. It measure different temps depending on how close I am to the stove burner, sides of the pot or surface of the wort.