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Temp Control and Data Logging

Kirk Keyes

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In another thread, the question of temp control and measurement came up.

I'm curious about approaches people have been using for controlling temperatures during emulsion making, and if anyone has tried to data log the temp readings so that one has a good record of the temperatures and times during the process.

I guess I should start - I've got a Corning PC-420 stirring hotplate and the temp controller probe that you can get for it. I find the temp controller to be a bit tricky to figure out what it's doing sometimes, it's not as smart as one could wish for. But then it's just a hotplate, not a computer... So I find that I have to set the temp on the controller lower than what I want, and let it heat up to below what I want, and then make smaller adjustments to get the temp where I want it, otherwise, it will overshoot the temp I'm trying to get to. Once I figured out that approach, it does a pretty good job of holding the temp where I want.

For data logging temps, I have not done anything fancy, just a pad of paper that I write what I do on it. I also record the time and temp if I think I need to or if it is changing. For time, I have a digital clock that I start at 12:00:00 when I begin the run and then all the times are easy to compare to each other and easy to record.

I know there are some pretty inexpensive digital thermometers with data loggers that are sold for use in high schools and other amatuer projects, and it seems like it would be cool to get something like that.

And for head control, is anyone using a heating mantle or heater tape to heat stuff up with?
 
Well, to be a purist Kirk, the ramp rate in degrees / minute is critical as well as other factors, so data logging is indeed useful, but these emulsions, at these scales, work just fine and are repeatable.

The ISO 40 emulsion has a bit of a problem when scaled very large, as the temperature changes involved change the ramp rate due to volume and this changes the digestion rate. I get a more polydisperse emulsion and less Iodide is churned to the top.

PE
 
That was a quick reply - certainly, data logging is not necessarily something needed, but it seems like it would be a useful think, when one gets more advanced in this field. But I'm just wondering if...
 
I don't know if you're looking for an off the shelf solution to temp data logging, or if you want to DIY to some degree. I just got one of these for Christmas http://www.adafruit.com/index.php?main_page=product_info&products_id=68 and it would be a good starting point for rolling your own. It's very flexible and not too steep a learning curve, and it will take single wire probes, control X-10 systems, and interface with Python, Processing, and many other languages for logging data over a serial or serial-USB port. You can get a card reader interface to log to a file on an on-board flash card. I've already made a lightning trigger for an electronic cable release. Search in google for arduino for other ideas and tutorials. The board and all associated software are open source, runs on Mac, Windows, Linux/Unix. Basic unit is about $30.

Lee
 
Lee,

Thanks for the link...this is more in line with what I am planning.

Kirk,

I found heater tape that is fairly inexpensive, and is available indifferent widths and lengths. I was considering using a deep pan of fine sand to hold the containers of solutions, and submerge the heating tape and thermocouples at different points in the pan to adjust and monitor temps. The only advantage there is that the tape and probes are held in place by the sand. The idea might be good for doing temperature critical film processing, etc., but not for this. I have a different setup in mind.

Bob M.
 
Lee,

I about fell out of my chair when I say you write "Arduino".

I spent a lot of time on Arduino and other microcontrollers which I find a million uses for.

Data and temp logging is probably the most common application that people write, and the OP could quickly put this together.

For me, however, I finally made up my mind that I can not do both hobbies simultaneously, micro development and photography, so I chose photography.
Steve.


 
optique said:
Lee,
I about fell out of my chair when I say you write "Arduino".
<snip>
For me, however, I finally made up my mind that I can not do both hobbies simultaneously, micro development and photography, so I chose photography.
Steve.
Click to expand...
Steve,

Yeah, it's hard to fit in all my interests, so I try to tie them together when I can.

While you're out of your chair, I grew up in Baytown.

Lee
 
Wouldn't a thermocouple and an ADC work? I'm not big into this sort of thing, but I know you can buy the little bi-metal sensors that attach to some volt meters pretty cheap, it seems like you could just plug it into an ADC and calibrate it w/ freezing or boiling water.

It's been a while since I've played with one of these but the last one I remember had a serial port hook - up with software included.

Anyhoo.

BTW im in houston too. Trippy.
 
Kirk;

If you wish to see a datalog, I have included it in the files I sent you after the Workshop. It includes flow rates, vAg and temperature datalogs for a hypothetical emulsion. It will be in the book. This run time data is critical to documentation of all Kodak emulsions.

PE
 
I remember that graph, the infamous one that got a whole thread deleted last year or so...

But that's kind of the way that I think would be cool to go. Temp logging is much easier than getting a pAg electrode running though.

You Houston guys should get an emulsion get-together going this summer and see what happens.
 
Yes, well, the graph was deleted but it will be in the book.

I guess there might be parts of that left hanging around.

PE
 
I'm glad that graph will be more exposure, I've got it in Bruce Kahn's hand-out. It is quite interesting.
 
totalamateur said:
Wouldn't a thermocouple and an ADC work?
Click to expand...

If you want to use a thermocouple you will also need a 'cold junction compensation' RTD (resistance temperature device or some other GDA). You will need an amplifier because a thermocouple will only put out a few tens of microvolts; the voltage developed is equal to the temperature difference at the two ends of the thermocouple wire, figure 40 - 60 uV/C depending on the thermocouple you choose.

One RTD can service multiple thermocouples if the terminal block where they are terminated is the same temperature all across.

Googling will bring up many examples. The processor used in the Adowhatsis board is an Atmel AVR ATMega chip. There is lots of information on the AVR available at 'AVR Freaks'.
 
Can you guys give more info on the Arduino and how it compares with other devices, like the BASIC Stamp? Easier, cheaper, more flexible?
 
Burr Brown makes a card that fits a PC slot and is covered with A/D and D/A converters. Between that and a USB, a lot of lab work can be done.

PE
 
Arduino is way cheaper than the BASIC stamp (last time I checked) and I find it much easier to program, coming from a C/C++/C# background. SparkFun Electronics has about the best collection of Arduino boards (there are many) I've seen. They also have lots of other cool sensors and stuff for electronics projects, although no good temperature sensors unfortunately.
 
Kirk,

I haven't used a Basic Stamp, so can't comment on them knowledgeably, and I'm just getting started with the Arduino.

I only found Burr Brown cards on ebay with a quick search, both ISA cards, one with 8 bits resolution and one with 32 bits. The 8 bit version had 16 IO lines. These would both have to remain hardwired to the computer. On ebay they were $200 - $400 used with no cables or software. Someone else will know a lot more than I on that score, and possibly have a better source.

The latest Arduino board basics are here: http://arduino.cc/en/Main/ArduinoBoardDuemilanove

6 analog inputs with 10 bit resolution
16 digital IO pins, 6 of them with PWM output
power 7-12 volts autoswitched to highest voltage input from USB port or standard coaxial DC plug (batteries or AC adapter).

If it matters to you, the Arduino is cross platform (Microsoft, Mac, Linux, Unix), hardware and software open source and licensed to be free (as in no charge for the software, you can modify it, pass it along with mods, and it can't be put under restrictive licenses in the future, and the board layout can be modified and produced by anyone without restrictions). The Arduino IDE is the same interface compiled for the different platforms. There are lots of libraries included with and available for the Arduino to make it easy to program a number of devices.

AFAIK, Basic Stamp is Parallax and a couple of clones. Their software is mostly (all?) free of charge, but more restrictively licensed, and may only be for Microsoft OS. I think there are third party IDE's for Basic Stamp under Linux that Parallax doesn't do support for. You can check the Parallax site to find out for sure. http://www.parallax.com/tabid/121/default.aspx

There is a lot of online support for both Arduino and Basic Stamp. I've found a number of online tutorials for Arduino. (I'm sure the same must be true of Basic Stamp.) I've seen articles in Make and Linux Format magazines on the Arduino, and I believe Nuts and Volts has also had some Arduino articles.

And Arduino is Java like programming while the Basic Stamp is like BASIC. Parallax also has an SX setup that's Java.

Lee
 
OK - here's a simple temp sensor setup with the Arduino:
Dead Link Removed
 
Use Timer$ in VB or C++ on a Windows machine to get the absolute time, or Timer.now - Timer.then (made up variables) to get offset. The value can be gotten by an In statement or other type depending on the language and port. For a parallel port, which was easy, it was a bit compare. For serial it is a bit (hah pun alert) harder.

PE
 
Kirk

IMHO you should join the forum at arduino.cc and spend a few days there first. You will make informed decisions then and end up having much more fun. WARNING: THE ARDUINO IS HABIT FORMING.

I can guarantee you will become well familiar with the concept/utility of the "serial terminal."

BTW, the arduino forum people are some of the most patient and helpful you will find (outside of apug that is!) As Lee indicates, Arduino net support is broad and deep.

Good luck
Steve.

 
Kirk,

It might be helpful to know what platform you're on, and what languages you have available or would prefer to use. I know I was looking at code last week for doing just what you want, python (a "free in all senses" programming language) reading the serial port (actually USB posing as serial) where the arduino was connected, the arduino supplying data at a given frequency to the port (9600,8,N,1), then a write to a file. I also found a polynomial fit for the data on a thermistor I had on hand (mfgr's data, not tested) that was within +/- a degree celsius over a broad range. There's also a system time call in python that's simple. Is there a language without one? There are more linear thermal sensors than a thermistor available. Parallax has some of those, as do the usual suspects, Mouser, Digikey, etc.

I was thinking that I might point you at some code, but after looking a bit decided that it would be too early to try that (way too many possibilities) when I don't know your OS or preferred computer language for communicating with the arduino and writing to files. Try looking at the documentation and introductory downloads at arduino.cc, read through some of the sample programs, look at the forae there, and that will give you a good idea of what's involved. You might be surprized at how easy it can be. Google on 'arduino thermometer' and browse what comes up.

Lee
 
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Lee - I'm running Win 2K and XP, and I can build a Fedora box if need be, but I kind of prefer to stick with windows. I can get around in Linux, but I'm not too fast with all the make/makefile stuff. Languages, I know Basic best, and when I say Basic, I mean like True Basic, not any of the VB versions that have come along over the years. I really don't know any others to that depth, and it's really been 20+ years since I've used it. I can muddle my way around Excel macros and HTML, I supposedly learned a bit of Pascal years ago. (The t-shirt that was popular at the time I was at Reed College was "Pascal - for those that can't C"). All I really remember is that I hated Pascal - too strict or something. I looked at Python for a half hour about 10 years ago...

So I guess I guess I'm learning something new, as far as languages go.

After that, I'd like the data in text or csv form and then I'll use Excel for my number crunching.

Lee - if you want to collaborate, I'm up for it. I've ordered a Arduino Duemilenova and a DS18B20 serial "one wire" temp sensor. That one looked like it had a bit more resolution than the other stuff I looked at. The DS18B20 seems kind of elegant. And being serial, I figured I could always just plug it into a serial port and use a program like Windmill serial software http://www.windmill.co.uk/

But the LM-34/35 temp senors looked easy enough as well, and cheap and easy to find. No fitting polynomials to any of the 3 chips I've mentioned.

I've got breadboarding stuff, and I'm able to understand basic electronics - I've build a MIDI interface for my old analogue synths from a kit as well as other mics projects like I did a shutterspeed timer years ago. It's not elegant, but it does work and reads down to 0.1 milliseconds.

I'm flexible on languages, so what ever you know, we can do. I see Python is available for Windows.
 
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