Need help designing a simple climate chamber

[vdustach]

Hello Eng-Tips, this is my first post. I'm a newly minted engineer and I am looking to put together a climate simulation chamber for my company. I'm going to need to control a heater and a humidifier and a dehumidifier. It's nothing very complicated and I'm just using simple tools from Home Depot.

T(in): need a thermocouple
RH (in): need a humidity probe

T(out): I have a baseboard heater rated for 120V, 750W to be controlled by PID. I'm thinking a Triac may be good for this.
RH(out): Supentown SU2000 ultrasonic humidifier on/off @ 120V, 60Hz
• Whisper 60 aquarium air pump on/off @ 120V, 60Hz

The aquarium pump will blow the chamber air through silica gel. I realize that will take a long time but thankfully the ramp rate can be low.

The machinery will sit below a mesh and I will be testing climate related stress and strain on the materials involved in picture framing. I bought several fans to mix the air as best as possible.

What kind of a control system would you suggest? I got a quote from AB but it seems quite high and the rep insisted I need an $860 display screen (can't I hook this up to a PC?). This is what he suggested:

1762-IF4
4 Channel Current/Voltage Analog Input Module

1763-L16AWA
MicroLogix 1100, 120/240V ac power, (10) 120V ac digital inputs, (2) 10V analog inputs, (6) relay outputs

1762-OB8
8 Point 24 VDC Source Output Module

2711C-T6C
6" Color (Transmissive CSTN) Touchscreen


I also spoke with Automation Direct briefly but he was pushing a controller without logic. I would like to use PID if possible.

Can anyone suggest an affordable but effective system? I am an admitted newb with designing control systems but I know how they work and I think I could handle the programming.

 

[danw2]

Well, I use single loop PID controllers (Honeywell UDC) because the next step will be likely be to ramp from temp A, soak at A then ramp to B and back again over a certain time, ya-da, ya-da. Single loopers can have an option for "setpoint programming" or "setpoint ramping" that takes care of such. Any single looper runs PID or on-off or time proportional PWM).

The temp control needs an RTD or a thermocouple (type T thermocouple has better uncertainty compared to type J or K)
For proportional control, get a 15A solid state relay to drive the heater element, drive it with 3-32Vdc signal from the temp controller.

For humidity control you'll have to buy an RH humidity sensor, typically with 4-20mA or 1-5Vdc output. They're powered by a 24Vdc power supply. A single loop PID controller with heat/cool capability with dual relay output will turn your humidifier/dehumidifier on or off as needed.

What you haven't mentioned is any sort of recording/data acquisition. All commercial environmental chambers have some sort of recorder attached (or flash memory in the HMI panel) to record the temp/humidity data. It isn't "control", but it proves the control works.

Your list of hardware is missing sensor stuff, and it isn't clear what the 24Vdc outputs are for. The heaters pull 7-8 amps so you'll likely need an interposing relay if the relay outputs aren't rated that high.

Make sure you are totally clear on what the programming software costs from A-B. It might well be multiples of the hardware costs. I don't know, I just hear lots of chatter about license costs from A-B.

 

[kontiki99]

There are off the shelf products for this sort of thing.

http://www.omega.com/pptst/CN3230.html

 

[vdustach]

kontiki- wow this looks perfect, I called Omega and the rep said the software was discontinued. Hopefully he calls me back with a replacement because that part including software is cheaper than the AB quote and is exactly what I need without programming. For my company's money it probably makes more sense to just do this and not put labor into programming. Of course, my boss wants to eventually build an automated matboard cutter so we would have to buy new controllers but for now it looks like a great option. Fingers crossed for the software!

danw2- I will certainly follow up on that if I can't make the Omega off-the-shelf component work.

Thanks everyone.

-Vincent