RTD Amp Ordered

A project log for Smoker Controller

A platinum RTC temperature sensor used to keep track of a BBQ smoker's temperature.

John BaichtalJohn Baichtal 04/11/2018 at 13:330 Comments

I ordered the RTD amp from Adafruit:

I was a little surprised that they had one. I had never even heard of RTDs before I started working at my current job. Adafruit even has RTDs to sell, though mine is better for my project because it has a magnetic coupling.

Adafruit's amp has ports for 2, 3, or 4-wire RTDs. So RTDs detect temperature based on the varying resistance of a specific alloy of platinum. This is great, but we can't forget that the lead wires have resistance too. Imagine if the room you wanted to monitor was 100 yards away--all that wire would dramatically change your readings.

There are two solutions. The first solution involves those third/fourth wires. 3-wire RTDs are quite common and use the resistance differential between the sensor+wire and just the wire to offset this bogus resistance. The 4-wire RTDs are even more ninja-like, creating a bridge circuit that provides a very accurate reading. The sensor I'm using is 3-wire, and I anticipate that will work perfectly for my needs.

The second solution simply involves using very short leadwires (= low resistance) in conjunction with a transmitter. The transmitter changes the variable resistance into a variable current--usually 4-20mA-- allowing clear transmission of data across any length of wire.

For the purposes of this project, the 3-wire configuration should provide all of the accuracy I'd need -- BBQ ain't rocket science!