Accuracy issues with Adafruit SHT41 temperature sensor

[thevenerablez]

Hi there,

I just got the Adafruit SHT41 Trinkey USB Temperature and Humidity Sensor: https://www.adafruit.com/product/5912

I want to love it since it seemed to tick the boxes for what I need for my project, except for one somewhat glaring issue. When I first plug the device in, it reads accurately. After it's been running for a few minutes, it heats itself up and makes itself wildly inaccurate.

The product description says "The SHT41 has an excellent ±1.8% typical relative humidity accuracy from 25 to 75% and ±0.2 °C typical accuracy from 0 to 75 °C. The reported temperature may be a few degrees higher than ambient due to self-heating"

I'm seeing this "few degrees" is actually quite substantial. I am in a room right now with 3 other thermometers from 3 other brands reading 67.1 ˚F, 68.0 ˚F, and 68.7 ˚F, and.

The Adafruit module is reporting 24.55 ˚C, which is 76.19 ˚F, which is 12% off the median of the other 3 sensors when measured in Fahrenheit.

My use case is to measure how comfortable the room is, so being 8˚F off is material. I am looking for a solution that does not need to be scientific, but overall reasonably accurate, regardless of whether the device was recently powered on or been running for hours or days. I don't mind it being a couple degrees off, but 76 vs 68 degrees in a room makes a big difference.

Should I return the sensor and find something else, or has anyone here had any luck calibrating, maybe subtracting off bias as a function of uptime? The issue is not necessarily that there is error, but that I don't have a reasonable model I could put in software to estimate the error.

--
Zach

[mikeysklar]

What sort of USB port is the SHT41 plugged (eg, laptop, hub, type-A extension cord)?

[sj_remington]

The sensor is not calibrated. The data sheet specifications are for a typical example, and give the range of expected deviations from typical behavior.

Try calibrating it, following Adafruit's excellent tutorial: https://learn.adafruit.com/calibrating- ... -calibrate

[T_Mo]

If it's plugged into a laptop USB port, I'd expect it to read substantially warmer than ambient.

Re: Calibration:
The spec for the SHT4x sensor says:

2 Humidity and Temperature Sensor Specifications
Every SHT4x is individually tested and calibrated and is identifiable by its unique serial number
(see section 4.7 for details on the serial number).

[adafruit_support_bill]

In the Trinkey version of the SHT41, the sensor shares a small PCB with an ATSAMD21 processor plus a linear voltage regulator and a Neopixel - all of which will contribute to the self-heating of the board. And plugging it directly into a computer USB port puts it in close proximity to yet another heat source.

I have two wireless temperature probes sitting on my desk right now. One is approximately 2cm from my computer and the other is at 20cm. There is a 3°C temperature gradient over that short distance. To eliminate the effect of any variability between sensors, I swapped the probes and allowed them to re-equilibrate and the gradient was the same.

[blakebr]

@thevenerablez,

Do you have a fan that you can use to stir the air around the sensors you are using? The laptop has a fan that expels the heat from the CPU, etc. Have the fan blow that heat away from your SHT41. If that normalizes the readings we have an answer.

I have several sensors near my desk. They read 78.8F, 77.4F, 77.2F, 77.9F. The first listed is a SHT45. The others are eBay/Temu specials. I have a heater under my desk because I am in a back corner of the basement and my toes get cold. The fan circulates the warm air so my tender toes don't get too hot. {grin} If I turn the fan off I get hot spots. HTH

All the data from my SHT45 is:
26.0C 78.8F RH 23.4%
3.5C 38.3F Dew Point (Calculated from the numbers above)

Bruce

[thevenerablez]

Thanks folks. I’m on an M3 MacBook Air, so there is no fan.

I’ve tried directly plugging the sensor into the laptop via USB A to C adapter, into a USB A to C extension cable, and into a USB hub. I figured some physical separation might help.

Unfortunately, the sensor is still giving significantly incorrect readings in all three scenarios.

[mikeysklar]

@thevenerablez,

Can you quantify the offset with the different setups? Initially you had reported 8 degrees higher with the laptop direct, but using the USB-A or hub I would expect this to be in within the "few degrees" higher that the guide page mentions.

[thevenerablez]

I got 7 degrees higher with the USB hub.

[T_Mo]

C or F ?