Temperature Sensor Conflicts

MobileMe

Active Member
I've been logging the temperature in my house in anticipation to move my furance over to the webcontrol board.  I started out with a waterproof digital probe from ebay.  It was very accurate and quick to respond to temperature changes.  Thinking of space and looks, I switched to a regular temperature sensor like this one.  I drilled some holes in a small box and mounted the temp sensor and a humidity sensor to the wall by the original thermostat.  The humidity sensor is working great, but the temperature sensor is not reading accurate at all.
 
I took the cover off of it thinking that it wasn't getting enough air exposer, but same results.  Then I took the sensor that was reading accurately, and mounted it next to the other one.  Now both are not reading right at all. 
 
Is mixing styles causing the problem? I wouldn't think so, but I don't know.
 
Mixing different sensors should not make any difference. However, how did you solder them would. The Dallas temp sensors actually sense the ground pin for the environmental temperature,. If you could please check to make sure the ground pin is not soldered to a big piece of metal leading to area you don't want to sense.
 
I soldered the sensor to a printed board so I could use terminals for wire connections.  If I have this right, the temp sensor is reading the wall temp instead of the air temp?  Well, that explains the difference in temperature.  The only thing that it does not explain is why the sensor that was reading well is not anymore.
 
We checked with Dallas semiconductor before.  They told us the design of their temp sensor is not sense through the black plastic, rather is to sense the temperature through the ground pin.  If the ground pin does not expose to the air to be sensed, or is connected to a large piece of meta leading to somewhere else, you will not get accurate reading.  If you have ground pin connected to a piece of metal leading to the area being sensed, that may help to get more accurate reading.
 
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