Webcontrol temp sensor reads high

[maxim775]

I deleted this and recreated here in the appropriate subforum, so I apologize if anyone has already read it. Noob mistake.

I am configring a webcontrol PLC (hardware 2.2.2, firmware version v03.02.17f) to monitor my home when I'm away on a trip this Winter, mainly in case my furnace fails. I've hooked up a DS18B20 temperature sensor as shown in the manual and it appears to read around seven degrees farenheit too high. I see nothing in the documentation about calibration, so I was wondering if either I am doing something wrong or if I simply need to account for the difference in software. If it is typical to have some offset, is it likely to be reasonably consistent? So far I've only had a small temperature window to observe it (63F - 65F). So far I've seen it vary from six to eight degrees high. I am using a 9VDC power supply (measures 9.15 V when powering the controller) rated for 675 mA which I believe is enough since I am driving no outputs. Thanks very much.
 

 

[az1324]

Where did you get the sensor?  If is a cheap china version then who knows.

 

[CAI_Support]

If you hooked up exactly like manual picture, the sensor picked up board temperature.  The manual picture is for helping to  identify the pin orientation. In real use, you will have a short or long wire that separate the board from sensor.  Please note that DS18B20 sensor uses its ground pin to sense temperature, not through the plastic shell.

 

[maxim775]

Amazon. Not sure of the origin but they have a 4.5 star rating.

I wondered if being so close to the board would matter but was surprised it made a difference that big. The ground pin sensing makes more sense in that regard. I want to put the controller in a case anyway, so I'll attach some wires. Thanks a lot.

 

[maxim775]

Did the trick. Reads very close to my thermometer now. Thanks again!

 

[CAI_Support]

Great to hear it working for you.