Simple Temperature Control System
Simple Temperature Control System
(OP)
Im a mechanical engineering student that knows a little bit about control systems (PID, control valves, feedback systems, etc.) but I need some help with a project that I am building.
I am trying to build a fairly simple control system for a 30 gallon water bath. The goal is to design a system that keeps the water at around 60 F +/- 1 degree. My idea is to use a water cooler/heater (like one you might find in the waiting room of a doctors office) and replace the hot and cold water manual valves with automatic solenoid valves that I control with a PID controller that gets its feedback from a thermocouple. I want the valves to open briefly (a few seconds at a time) to let in just enough water to affect the temperature depending on the changes of the water bath. I dont necessarily want the water to be constantly flowing. The excess water will overflow to a holding tank to be pumped back up to the water jug that sits above the heater/cooler unit to keep the water loop closed.
I have a basic idea of how I want everything to work, but I dont know exactly which controller I should buy, which power supply, and which thermocouple/thermocouple cable. I've been looking at automationdirect.com at some micrologics plc controllers as well as the single loop temperature controllers, but Im afraid I will get the wrong one for the job. I want to use automatic sprinkler solenoid valves ($15 each) which require 24V AC to actuate.
I should note that I have a bit of programming experience with C++ and a little bit with Allen-Bradley 'ladder logic' so I understand at least the logic and basics of programming controllers.
Can anyone please help me to decide which controller, thermocouple, couple wire, and power source I need to buy for this pretty simple design?
I am trying to build a fairly simple control system for a 30 gallon water bath. The goal is to design a system that keeps the water at around 60 F +/- 1 degree. My idea is to use a water cooler/heater (like one you might find in the waiting room of a doctors office) and replace the hot and cold water manual valves with automatic solenoid valves that I control with a PID controller that gets its feedback from a thermocouple. I want the valves to open briefly (a few seconds at a time) to let in just enough water to affect the temperature depending on the changes of the water bath. I dont necessarily want the water to be constantly flowing. The excess water will overflow to a holding tank to be pumped back up to the water jug that sits above the heater/cooler unit to keep the water loop closed.
I have a basic idea of how I want everything to work, but I dont know exactly which controller I should buy, which power supply, and which thermocouple/thermocouple cable. I've been looking at automationdirect.com at some micrologics plc controllers as well as the single loop temperature controllers, but Im afraid I will get the wrong one for the job. I want to use automatic sprinkler solenoid valves ($15 each) which require 24V AC to actuate.
I should note that I have a bit of programming experience with C++ and a little bit with Allen-Bradley 'ladder logic' so I understand at least the logic and basics of programming controllers.
Can anyone please help me to decide which controller, thermocouple, couple wire, and power source I need to buy for this pretty simple design?





RE: Simple Temperature Control System
If this is a real world application this may be a simpler and cheaper way to go.
If this is a problem posed by your instructor, sorry. We don't do homework.
Bill
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"Why not the best?"
Jimmy Carter
RE: Simple Temperature Control System
As far as the electric heater goes, this will not really work because the bath needs to be a cold-water bath, that sits below room temp. That is why I have the water heater/cooler, so that I can add cold when it rises above 60 and hot if it drops below.
Is a PLC too much? I might also eventually like to add a level sensor and a signal to the pump, but that doesn't need to happen right away.
Is a thermocouple too much? Can I get a cheap (but relatively accurate) thermometer to send analog signals to the controller?
RE: Simple Temperature Control System
You might want to look into those solid state heater-cooler chests. A solid state heat pump controlled by a simple PID controller may be the way to go.
Google "Peltier Effect" The Peltier Effect is reversible by simply reversing the direction of the current.
Here is a link to one example.
http://www.thermonamic.com/TEC1-01703-NET1.pdf
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Simple Temperature Control System
RE: Simple Temperature Control System
Single loop controllers already have their HMI built in, shows you the temperature and setpoint. An HMI is a separate device oon a PLC, in many cases different software, 2nd learning curve.
>Is a thermocouple too much? Can I get a cheap (but relatively accurate) thermometer to send analog signals to the controller?
I suppose you can shop the 'net for an oddball "thermometer with analog output, but will the analog output be a conventional industrial signal (4-20mA, 0/1-5vdc)? Stand alone controllers can take thermocouples direct, analog cards for PLCs are usually specific to thermocouple or RTD or current/volts. Buy a $15 thermocouple and be done with it (type T is best for near ambient, spend an extra buck for ungrounded and an extra buck for limit-of-error)