PID Temperature Controller
Overview
These are just some notes in case I actually getting around to building my own controller for the Sous-vide Immersion Circulator (instead of using an off-the-shelf bang-bang PID controller)
Processor
(not yet selected)
Display
(not yet selected)
PT100 Interface Chips
All three of these parts are somewhat expensive. They are, however, 24-bit A/D's, so they'll have really good resolution. It's possible to build an interface from discrete op-amps and run it into an A/D on the processor. However, most processors only have 10-bit A/D's, and usually have a couple bits of error. For a 0-100C temperature range, which is about 0.2C per bit. At 24 bits, that's about 0.00001264C per bit. A little "bit" more accurate...
Datasheets
- Analog Devices AD7709ARUZ ($4.63)
- Analog Devices AD7711 ($23.83)
- Linear Technology LTC2402CMS ($6.50)
- Texas Instruments ADS1248
Application Notes
- RTD Interfacing and Linearization Using an ADuC8xx MicroConverter (Analog Devices)
- 1- and 2-Channel No Latency DSTM, 24-Bit ADCs Easily Digitize a Variety of Sensors, Part 2 (Linear Technology)
- Positive Analog Feedback Compensates PT100 Transducer (Maxim)
- Precision Temperature-Sensing With RTD Circuits (Microchip)
- Practical RTD Interface Solutions (National)
- Complete Temperature Data Acquisition System From A Single +5 Supply (TI)
Power Control
Ideally, an IGBT circuit would be used. These are more polite on the power line, as they're turned on at the zero crossing, and turned off part way through the cycle. Triac circuits are just the opposite. IGBTs also supposedly run cooler.
