Webcontrol temp sensor reads high

[maxim775]

New to this forum, and I apologize if I missed a similar topic in my search. 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 have hooked a DS18B20 temperature sensor up as shown in the manual and it appears to read about eight degrees 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? Thanks very much.

 

[maxim775]

That's eight degree farenheit, FYI.

 

[maxim775]

Adding infromation as I think of it; sorry for the additional messages. My power supply is 9 VDC (measures 9.15V when the PLC is running) and is rated for 675 mA which I believe is enough as I am driving no outputs.

 

[maxim775]

I didn't realize the ground pin was the sensor rather than the case, so the board was influencing temperature much more than expected. Adding some wire solved the problem.