Programmable Water Temp Controller - how to make?


Thread Starter



Hopefully someone can help me, and I've picked the right type of forum. I'm a student on a budget and have a project that would be so much easier with automatic control.

What I need to do is increase the water temperature of a bath by 1C every hour. I would need the set water temperature kept constant between temperature changes. I have a continuous source of water and all I need to do is increase that water temperature.

Here is what I am picturing:

- a flow-through holding tank with water flowing in at a rate that won't see the bath increase in temperature with heat from the room

- a heater submerged in the bath

- a digital, programmable controller that will switch the heater on/off to heat the water to the set point and then maintain temperature in the bath until the next temperature

How can I do this?

I have no idea how to set up controller systems. I have lots of heaters and stuff, it's the programmable control that's the tricky part. I was looking at something like this:

Thanks for any help and ask me anything!

curt wuollet

For control that close, you will also want to stir the water in the tank. As to how to set up the controller, that will depend a lot on the controller you choose. If the tank is such that there is reasonable dwell time, you should be able to do this with anything from a PLC to a profiling controller. With a PLC with a real time clock you would simply set up a temperature control loop with a register holding the set point and once that works set up a timer or compare to the RTC that will bump up the register at the rate desired. To keep it simple you want to limit the heater power to just over what it takes to raise the temp one degree per hour.

There are numerous commercial Temperature controllers, like the one you linked to, that are also 'programmers' or 'profilers', where the terms come from 'setpoint profile program'; a preprogrammed means of automatically adjusting its own setpoint over a period of time.

Setpoint increases or decreases over a period are called 'ramps'; a period when the setpoint is constant is a 'soak' or a 'hold'. Each ramp or soak is a 'segment' in 'profile'.

It isn't clear whether your activity requires holding a SP for an hour, then increasing 1° (a step change); or whether you need to increase 1° per hour continuously, but the profile programs can be setup to do either step changes or ramps.

I didn't see that the model you picked out had a programmer feature.

The one here does:
There are dozens of others.

I'd suggest either a 3 wire RTD or a type T 'special limit of error' thermocouple as a sensor for the range you are working with.