Need to control 16 digital outputs based on 16 analog inputs

[Craig]

Hi,

Here is the situation.
I need a way to control 16 lamps based on the input of 16 thermocouples, so one thermocouple per lamp (the lamps are used to heat carbon-fiber products for curing). I would need some sort of device that has 16 analog inputs and 16 digital outputs.

The programming would have to allow the ramp-up of temperature at a certain rate, hold it there for a specified amount of time, ramp up again, hold again, then turn off.
For example:

Ramp up at 5 degrees per minute,
Hold at 200 degrees for 120 minutes,
Ramp up at 5 degrees per minute,
Hold at 275 degrees for 300 minutes,
Turn off.


We would also need to keep a log of this, with samples every 1 second or so.

I have looked around, and everything I found is either extremely expensive, or just doesn't have enough analog inputs. There seems to be a ton of stuff out there with digital inputs, just not with analog.

Do you guys have an idea if what I could build that perhaps uses a USB connection to hook up to a PC to do this?

Thanks,

Craig

[Chris Smith]

This is one area where the pic / stamp comes in handy.

Time to learn the programming.

[haklesup]

Traditionally one would choose a "Process Control" system and select a bunch of DIN temperature controllers. But at $200 per channel for basic controllers and more for ones that can be networked it can add up fast. but even a $5k cost for capital equipment does not seem unreasonable for a business.

Here is an inexpensive controller. It will be easier not to try and find an instrument that will do all 16 channels at once, just do it one at a time and link everything serially to a PC (personal computer or process controller).
http://www.nimerion.com/prod/tc_16b.html With these plus the cost of the thermocouples and control relays, you could do it for around $2k.

Search on "process controller" and "DIN Temperature" Tons of hits with either term. You'll be sure to find one with all the features you need. I didn't see it in my brief search but I know software is out there that can draw your temp profile as a graph then transmit it to the controllers.

As a DIY, a single temp or manually adjustable system would not be too hard but your temp profile program is complicated enough to require a processor of some sort which complicates the problem significantly. Even if you could design a suitable system yourself for less than $1k, it would take weeks or longer cutting into your productivity at work and delaying implementation of the hardware. In my tiny company such a purchase would be easily justified even though we have several EEs capable of the task.

DataLogging should be possible if the controllers are connected to the PC but if you just go with stand alone controllers you could not easily collect data without a seperate system. It depends on the software and hardware you select.

[Newz2000]

Are you looking for a do-it-yourself project, where you solder parts to a circuit board and write a little program to control all of this?

Things to look into:
Microchip PICs
Basic Stamp
Dallas DS1820
Phidgets
www.Sparkfun.com

You can use the common Dallas DS1820 to read the temperature of many sensors using only one i/o pin (digital, not analog). You can use a common shift register to control dozens of lamps using only three or four i/o pins. Therefore, you really don't need a lot i/o to do this.

Give us more details about what you're thinking and we can better point you in the right direction.

[Clyde Crashkop]

You might look into the 4051 bilateral switch chip. 8 analog inputs addressable to 1 analog output. 2 of those would get you from 16 down to 2 inputs. Then 2 A/DCs.

[Craig]

Hi Guys,

Thanks for all the replies! I have looked at microcontrollers such as the PIC and Basic Stamp, but none of them have high number of analog inputs, and since each thermocouple requires two inputs, that cuts it down even more. We are ok with spending up to about $3000 for this project. If you're curious about our company, you can check out the website at http://www.comtekadvanced.com.

I am ok with building something from scratch and/or programming a microcontroller. I have never done it, but I'm confident that I can figure it out.

This project isn't an urgent matter, but it is something we need to have running in the next 3-4 weeks.

I will do some searches on process control and DIN temperature. We already have the thermocouples; we just need something to hook them up to.

I have found this neat little package which seems to have what we need.
http://www.mksinst.com/product/Product. ... ductID=199
I am in the process of working out the configuration we need so we can get it quoted. I will post back with the quote to let you guys know.

Craig

[philba]

Get an analog multiplexer and you can read a lot of analog inputs. for example a 4051 will allow you to take 8 analog lines down to 1. so you just need 2 of those and 2 analog inputs on the micro to manage 16 analog inputs.

I'd look into the PIC18F series. Use a few lines to control the analog multiplexers, use 16 pins to control TRIACs to control the lamps, serial output for logging, maybe use an LCD display to give status.

I would not use a Basic Stamp for this application.

look into PID control to manage the temperature.

Why are you using thermocouples? there are cheaper solutions in that temperature range.

[MrAl]

Hi again,

I think you can get down to around 10 dollars per channel using
a few PICs. Some of the PICs have 8 analog inputs, so that gets
you going maybe with 4 channels per chip, or heck, even 2 channels
per chip will mean low low cost. Even one chip per channel means
low cost, with each chip controlling it's own lamp through an i/o pin
and a driver. This would be WAYYY under 1000 dollars, maybe
at the most 100 bucks. It will be hard to beat that cost.
Dont know what kind of thermo sensor you are using so you might
need an amplifier per channel for that. With the amp that means
only one input per thermo sensor too, not that it affects cost that
much anyway as the PIC chips can be had for 2 dollars each.

Turn around time will be a bit longer unless you've had some programming
experience.

[Colinr]

with a 3 to 4 week time scale you may need to considering purchaseing off the shelf data acquisation hardware and spent the time with getting the software working

check out national instruments www.ni.com They specalise in data acquisation cards for PC's most cards will handel 16 analogue inputs and have more than enough digital outputs.

as a suggestion the pci 6025E card will fit your requirement.
to connect to the card you will need a sh100100 cable and SCB-100 connector box


Colin

[ljbeng]

Have you looked at a PLC yet?

Go to www.automationdirect.com

They have the best prices. Select a CPU type and add as many analog modules as needed. You could have relay or solid state outputs. The CPU will allow PID loops which is the type of control usually needed for temperature. A DL06 would probably work. 16 channels of AD may cost you though.

Quan (4) F0-04THM $199 ea (Thermocouple AD input cards)
Quan (1) DL-06DA $259 ea (16 AC outputs)

Add a datalogger... www.ljbeng.com

[ljbeng]

Forgot the software...

PC-DSOFT5 $395