Best temp sensor for local application?

[Eric Nelson]

Eric Nelson, would your solution involve the fan being on constantly, then?

Actually, no. If there is no need for cooling, then the fan is off.

Think of it this way... Let's say you had TWO fans, each controlled by a separate output from your programmable relay. If the temperature is, say, 1° above setpoint, turn on one fan. If running one fan for a minute or so doesn't lower the actual temperature, turn on the second fan to double the airflow. In other words, only use as much airflow as needed to change the temperature.

Think about how you use the multi-speed fan in your car's cabin heater. You might turn it on full blast to quickly heat up the car, but once it's warmed up, you don't turn it off completely, then back on full blast when it cools down again. You adjust the fan's speed as needed to maintain a comfortable temperature.

My thought was to just use one fan, and select different voltages going to the fan. Low speed = half voltage, High speed = full voltage. Now that I think about it, it might actually be easier to just use 2 separate fans (with different CFM ratings). As an example, Fan 1 would be 10 CFM, and Fan 2 would be 20 CFM. By only using 2 outputs, you can have 3 different amounts of airflow. Fan 1 on = 10 CFM, Fan 2 on = 20 CFM, Fan 1 AND Fan 2 on = 30 CFM.

Also keep in mind that you can do the same thing with your heating pad(s) to affect how fast the temperature rises. Oops, looks like you're gonna need more I/O now!...



-Eric

 

[Turkey B]

Ahh, I see, Eric. Heh, not only will I need more I/O, I'll probably need a bigger device box! Sounds pretty good though. I'm doing my temperature tests tomorrow and after that I will begin considering whether to slow down my 24CFM fan and possibly multi-speed control it, depending on how fast the tank heats up of course. I have a small 120v control relay hanging around somewhere...

I've also been looking into sensors, including those suggested here, and I was wondering if anyone had any comments on the LM35 from National Semiconductor?