Temperature out by 10 degrees C?

[bugz_nz]

Hi guys,

I've had a couple of temperature probes attached to a module for a while now and they have been working great. I recently updated one of my modules to the C4.1 firmware and now the temperature being displayed by both probes seems to be out by 10 degrees.

That is to say, the first probe used to read around 19 degrees C and now reads around 9 degrees C and the other probe which used to read around 40, now reads around 30.

These probes are in my server room and I can assure you that the temperature hasn't dropped ten degrees overnight.

Any ideas on what it may be?

[jason]

If it's possible can you take the probe ends our of your server so they reach temperature?  Then you can at least see if they match and are accurate.

[bugz_nz]

Hi Jason,

Unfortunately it's not possible to remove the probes as they are inside a production server.

I have just tried the temperature probes on another module though, which is still running the C3 firmware, and the temperatures seem to be correct to what they were before I upgraded the main module.

[bugz_nz]

The same probe reads different temperatures on each module:

On C3 firmware:

18.2C

On C4.1 firmware:

15.4C

So the 10C gap is not constant, but there is still a gap between the two, using the same probe and settings.

[jason]

I just ran a side by side comparison of C3 vs C4.1 with the same temperature probe.  They were giving identical readings.

I can't think a situation in which the firmware could lead to measurement errors like that.  3 degrees is small enough that it could be because of noise of equipment grounding. 10 degrees is quite a bit.

I looked in our server logs and found the time period when you upgraded.  There was quite a gap in time between the two readings:

Tue, 01 Dec 2009 01:45:39 GMT - Channel 1: 16.8 C
Tue, 01 Dec 2009 01:45:44 GMT - Channel 2: 31.3 C
Tue, 01 Dec 2009 19:39:00 GMT - Upgrade to C4.1
Tue, 01 Dec 2009 19:41:15 GMT - Channel 1: 9.3 C
Tue, 01 Dec 2009 19:41:19 GMT - Channel 2: 26.9 C

You know your server better than I do obviously, but is there a chance the temperature actually changed that much over the 18 hour gap?


 

[jason]

Actually I did just think of another possibility.  Some corrosion may have developed on the pins of temperature probe.  When you unplugged/replugged during the upgrade process, it may be making contact in a slightly different spot and making the reading different.  If that is case, unplugging and replugging a bunch of times may clean the contacts a little and get you pack to the original readings.