User:Andy Maloney/Notebook/Lab Notebook of Andy Maloney/2010/06/17/Temperature stabilization

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Objective heater

I have finally finished my objective heater build and tested it to some degree. The only issue I have with the setup right now is that measuring temperature and having the computer log it is somewhat of a problem still. Other than that, the system works spectacularly and is relatively cheap. It's actually a lot cheaper than the commercially available units and it was fun to build.

Materials

  • Temperature controller.
    • I should note that TeTech has an OEM version of this controller that I must admit I like better than the one that has the LCD readout. Mainly because the program is much more intuitive to control than the LCD push button readout. But, both work spectacularly and it is nice to be able to read off the temperature of the controller easily.
  • Objective thermal spacer.
    • This is just a piece of ABS with the right RMS threads on it. It's remarkably expensive but I supposed it is worth it since finding the RMS die is rather difficult for some reason. You can get a tap pretty easily from Thorlabs though.
  • Power supply.
    • I have never had problems with MeanWell power supplies.
  • Box and Box cover.
    • This is to safely house your power supply so that you don't shock yourself.
  • LEDs.
    • These are to indicate when the power is on.
  • Switches.
    • To turn on the power supply.
  • Flexible heaters.
    • I really like this stuff. Resistive heaters that you can cut out and use almost anywhere.
  • Copper tape.
    • You don't have to use this type of tape as it is somewhat pricey. It's what I had available but you can also use aluminum tape. Of course you won't get the same NASA space looking affect on your objective with aluminum as opposed to copper.

Build

The temperature controller comes with a thermistor of which, I put banana connectors on the ends of the wire. The reason I did this is because I didn't feel it was appropriate to have exposed wires/terminals on the temperature controller. Mainly because there is a possibility to have high current going through them. So, I built a small box as a cover. This turned out to be a tremendous nuisance and another reason why I think using the OEM temperature controller was probably a better choice. But again, I'm conflicted since I like the LCD readout a lot.

I just taped the thermistor at the base of the objective. This required some tape massaging in order to get it to stick properly using the copper tape.

Once the thermistor is on the objective, you can put the flexible heating element on it. Thankfully the stuff from Omega has a sticky back to it so just peel and stick it on the objective. I've been using for about a week now and have had no problems with it. As you can see in the picture, There are 2 alligator clips attached to the heating element. I had to do this since I couldn't for the life of me solder anything to the leads. Those wires run to the temperature controller and connect to it via banana connectors.

The power supply is housed in the aluminum box. I'm not going to go through the complete build for it. Suffice it to say, if you don't know what you are doing in the area, be careful or let an expert do it since you will be working with power from the wall. The circuit diagram for it is below.

The important thing about the box is to make sure you connect the box to earth ground. Also, you should put a fuse in it just as a safety precaution to protect the power supply. I chose to have a main switch to power the power supply (green indicator LED) and another DPST switch on the front to turn on the +12VDC output to the temperature controller. This may be overkill but I got to use 2 LEDs with this setup. The green one shows the unit power on and the yellow one shows power to the temperature controller.

If I could have found a bigger switch on the front, then I would have put that one in. Why? Because everybody loves switches.

Right now I have another K type thermometer hooked up to the objective to measure the temperature via a NI USB 6009 and a Fluke 80TK meter. This is a terrible setup and I am thinking about switching to a PT100 as the measurement device.

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