Electronic – Building a temperature-controlled water bath

control systempid controllertemperature

I want to build an accurate (±2 °C) water heater (sous vide) that heats water somewhere between 30-100 °C according to user input.

Although I have an engineering background I have no experience whatsover with building controllers and have no clue on how to start. I don't want to spend to much money on the project (< 100 €) thus money is an issue. The good thing is that I already have a power thyristor.

What I (probably) need:

  • Temperature sensor PT100
  • Input device to define water temperature (digital?)
  • Controller (PID?)
  • Resistor to heat the water (can be taken from old water cooker I assume)

My question is how I can best make the link between the sensor and the heating element. I of course need to build/program a circuit that does this but do I make an analog or digital circuit?

I have a thyristor but is this really necessary or should an on/off regulation also work? Don't forget that I also should be able to define the water temperature.

Any help is greatly appreciated (also useful links).

Best Answer

I just put together a sous-vide setup with a commercial PID. Originally I had planned on using a crockpot/slow-cooker, but was able to pick up an indoor turkey fryer via a post holiday sale.

My setup & costs:

  1. JLD612 PID temperature controller ($33.50)
  2. PT-100 0.1 degree Thermocouple ($19.00)
  3. 40A Solid State Relay ($16.50)
  4. Indoor turkey fryer ($25.00)

The JLD612 is pretty much self-contained, and has displays for current & target temperatures. It also has an auto-tune feature that configures the PID parameters for your particular setup. A downside is it's workings are a bit of a black box -- you don't really know what's going on inside. On my To-Do list is to build a combination PID/data-logger on the Arduino platform.

FYI, Make Magazine just had a Sous Vide Immersion Cooker project using a similar PID controller.