when changing emissivity, temp reading becomes wrong "ex:-128 Object , 600 Ambient"

[AlmousaM]

I'm using the example provided here to change the emissivity, but once I do that I get wrong temperature reading and I have to unplug the Arduino and replug it again to get correct readings again. I'm not sure if this is a hardware or firmware issue

[otecfuras]

We're having similar problem with invalid temperature values, though we're not sure that setting emissivity is the main culprit. Our procedure is as follows (simplified):
SETUP:

• start I2C communication
• set measuring units to Celsius
• set emissivity (regardless of the current value, so we often replace value stored with same value)

LOOP:

• do 30 times: { ...; mlx.read(); float t = mlx.object(); ... }
• wait/sleep 10 minutes

Recently we experienced this issue few days ago, readings were as follows:

...
2020-12-04 15:19:08: 2.23;2.15;2.47;2.19;2.19;...;2.37;2.29;2.59;2.31;1.91
2020-12-04 15:29:06: 2.07;2.53;2.47;3.45;2.31;...;2.59;2.53;2.37;2.17;2.17
15:39 device (feather m0) restarts for unknown reason
2020-12-04 15:40:05: -94.79;-95.47;-75.91;-93.25;-91.75;-92.19;...;-95.89;-92.67;-98.53;-92.51;-95.15
2020-12-04 15:50:05: -96.45;-94.65;-95.11;-95.55;-93.93;-93.75;...;-91.91;-95.71;-96.07;-95.15;-95.47
...
device restarts intentionally after 3 measurement cycles (every 20 minutes) in order to fix MLX error
...
2020-12-04 22:49:31: -97.55;-93.37;-89.29;-92.65;-95.29;-94.43;...;-93.31;-95.85;-91.73;-95.11;-91.51
after approx. 8 hours of restarting, MLX suddenly started to return valid data
2020-12-04 23:00:22: 2.15;2.07;2.27;1.97;2.31;1.87;...;2.27;2.43;2.59;2.05;2.65

Do you think this is the same issue as yours?
Have you found any solution/workaround?

[AlmousaM]

@otecfuras it seems like the same problem that I'm facing. I am using now Adafruit MLX90614 library; it still have the same problem when changing the emissivity, however it happens less often

[dmalawey]

I'm also having this issue. Both ambient and object temperatures are large negative values such as -627.57C object and -127.87C ambient temp.

If I wave my hand in front of the sensor, the object temp increases from -137 to -77 so it is still taking readings.

Using the Adafruit library, I had the same problem.

When I reset the sensor using therm.begin() it sometimes corrects the readings. Sometimes not.

[dmalawey]

There is a root cause found regarding this issue, but not a countermeasure. If you have control of the power pins, you can power cycle the sensor after changing emissivity.

Details are here
adafruit/Adafruit-MLX90614-Library#32