Inconsistent temperature readings

(Gray) #1

I have two SmartThings Multi sensors sitting next to each other, and one is reading 65F while the other is giving 67F.  They’re sitting on top of a thermostat reading 70F and under a thermometer (which I trust more than the others) reading 69.2F.

Is anybody else seeing this sort of variation in reported temperature?  Is there any way to calibrate temperature readings on these sensors?

(Hfb) #2

I’ve noticed on some of the logs, some of the inconsistency seems to stem from the battery voltage/reading. Sometimes, it’ll show 100% and a specific voltage. The next minute, the battery will show 103% and the temperature will jump 0.5-2.0 C.

I also noticed, like you, the temp sensors all seem to read a little lower than expected. I haven’t gotten around to pulling one apart to see what sensor they are using but I’ll probably get around to it this week to check that.

(Andrew Urman) #3

@gray the Multi’s are rated at +/- 2°F

@healthyfatboy thats an awesome observation! I’ll do some similar testing on my end

(Cory S) #4

Mine have been surprisingly accurate. They have been within half a degree of my highly accurate Thermaworks handheld.

(Hfb) #5

It’s also possible that the other thermometers I have are off but I find it odd that 5 other thermometers I have are all within 1 F of each other while these have been low by 3 F or so.

(Brianh) #6

Mine also are off. I am about 5-6 degrees off. My Nest thermostat and my Fluke meter read the same temp but the sensors are off.

(Brianh) #7

I just checked my multi’s and 2 say 70 and one says 69 but my recently calibrated Fluke 179 says 75 and my Nest thermostat says 74. That’s too far off for me.

(Hfb) #8

I have been checking mine again against other thermometers I have been using along with our thermostat. I set one multi on top of the thermostat and then another next to an indoor thermometer. I also have two multis next to outdoor thermometers that are in the attic spaces. I have found that all of them are off by about 3-5 degrees, which is very much out of spec for the temperature sensor being used for some of the multis I have. That’s quite a bit of a difference and is a problem for me. If it’s a constant offset, then I can mentally account for that difference but I shouldn’t have to.
I’m also looking at the logs and I don’t know what scale is being used for the data it’s outputting but when the battery voltage value changes by one unit, the temperature value changes by 7 units. I’ll have to throw one into the fridge or freezer to see how it changes because some of the data I’m looking at isn’t in much of a steady state with the house warming and cooling throughout the day but the battery value changes happen within a few seconds of each other so it’s not the temperature changing much but a function of the battery voltage.

(Pmsmaker) #9

@Andrew, Do you have any updates from your 5/22 post?

Here is what I got - These are all stacked on my Thermostat
Multi 71
Dallas Logger DS1820 76.1
Honeywell Digital TStat 76
Mercury Bulb1 76.8 from Bacharach Sling Psychrometer
Mercury Bulb2 76.8

If the Multi specs are +/- 2°F that is bad enough - Unusable for some applications.
My data looks like - 5°F + = similar to what others are saying = completely unusable.
BTW - the Aeon Multi says 50°C / -4°F to 122°F - Accuracy: ±1°c = *9/5 = 1.8 F

Let’s see what Andrew’s follow-up is.

(Hfb) #10

I’ve been keeping track more by sending my data over to ThingSpeak and found that when the battery voltage changes, it also affects the temperature data. It’s been kind of aggravating but it’s something I can compensate for. I just haven’t gotten around to it.
I don’t know why it’s consistently 5 F low but they have said that they plan on allowing for people to add an offset in the app. It doesn’t solve the problem but tit’s at least a way to get it looking correct. I suspect there’s a hardware design issue.

(Chrisb) #11

If the temp is being changed by voltage it’s a bummer that they didn’t put a plug option in it like the Motion Sensor has. Obviously it wouldn’t work for most door situations, but if someone wanted to use it for temp then at least there’s a constant level of power.

(Cory S) #12

You could probably make a plug in for it. Hacky, but mines covered in a hot glue condom right now so…

(Pmsmaker) #13

It is not the voltage to Chip - IMO.
As hfb says, it is most likely a hardware(board) issue. :frowning:

(Chrisb) #14

I wonder if something like this could be made to work with SmartThings?

(Iron Buckeye) #15

I’m not being as scientific as some of you, but I’m seeing WAY more variation. Currently I have two Multi Sensors and two Moisture Sensors sitting side-by-side inside my freezer. The Moisture Sensors are both indicating that a freeze condition exists. When I went to bed last night, one Multi Sensor indicated 35 degrees, the other indicated 68. This morning the Moisture Sensors are still indicating a freeze condition, while one Multi is indicating 74 degrees, the other 75. I’m quite certain it is not 70+ degrees in my freezer (judging by the frozen ice cubes located 4 inches away).

Anyone else seeing this type of behavior?

(Cory S) #16

@jhardt, The multi sensors have that issue in extreme cold. After about 32 degrees they actually start increasing temp for every degree dropped dramatically. I have a thread on it somewhere troubleshooting why it was behaving like this in my kegerator.

(Iron Buckeye) #17

Well, thank you. Your post was quite helpful. The behavior of the Multi-Sensors… not so much. That behavior makes them essentially useless for what I had intended to use them for (monitoring temps in my detached garage).

(Chrisb) #18

@coryds … Did you look at the brewbit on Kickstarter at all? I wondered if this is something that would help in your situation?

(Cory S) #19

@chrisb, yeh the brewbit looks awesome! I really don’t have the patience for kickstarters though. Their expected delivery time is March, and we all know how those dates slide.

(Lucas) #20


Others of the Smartthings team have suggested we do not use Multi-Sensors for extreme temp conditions. I am in the process of looking for a better cost alternative for temp monitoring for frozen environments.