Friday, December 13, 2013

CryoBUG Project Resumed

Well its been a long time since my previous posting, and a lot has transpired over the last few months. A truly Green refrigerant charge has been developed, utilizing only hydrocarbons (HC) and Argon, which promises to give me even better cool-down times and stability.

The chart above reflects a heat load of approximately 10 Watts on a copper High-Mass Cold Head that is utilized on the CryoBUG Demo unit.

Since I was already using some HC refrigerants in my blend to begin with, it always kinda of bothered me that I was still reliant on R-14 an HFC. Besides being a high GWP gas, R-14 also carries a very hefty price tag. So after experimenting with some other HC gases, I was able to zero in on a combination of 4 gases which not only worked in place of any HFC's, but also offered superior capacity and stability. 

During my experiments I did have a series of mishaps. First I fried my DAQ temperature test & monitoring hardware, and then I started to notice erratic behavior in my unit control electronics. The DAQ problem was easily, and luckily, cheaply fixed by  the manufacturer Measurement Computing. The control electronics unfortunately wasn't so easily fixed. It is a design flaw, and something attributable to using components outside of their intended specs. So back to the drawing board.

On my original control system I was intentionally avoiding the use of a microcontroller, because of concerns with electrical noise issues and just being a bit lazy about programming. Anyway I decided to bite the bullet, and have opted to design a new control board around an embedded microcontroller chip. To make things a bit easier, the initial design will utilize a ECIO-28P from Matrix Multimedia as my controller base.

  1. USB connection
  2. PIC18FX455 microcontroller
  3. 4Mhz ceramic resonator
  4. Power/Programming LED
  5. Reset switch
  6. Power selection jumper
  7. Device pins - 0.6" DIL
Picture shows ECIO-40P. ECIO-28P is similar.

To make the programming easier, Matrix's FlowCode application is being used, which as the name implies sports a graphical flow chart approach to coding. In fact it's so easy to use, that I was able to write my entire code, simulate it, and then write it to the ECIO and test it on a protoboard all in one day. It was also nice to see the simulation mimicking the hardware test results.

A piece of the CryoBug controller's FlowCode showing simulation panel...

I really enjoyed this aspect of the project, and wished I had just done it this way in the beginning. Using a microcontroller also allowed me to easily accommodate some extra features that were very much needed.
  • Remote now overrides local ON/OFF control for the compressor, and works in a steady state mode, unlike local, where the switch action is momentary toggled ON/OFF.
  • Delayed restart following a momentary shutdown, in order to allow compressor pressure equalization, for easier start-up and less amperage draw.
  • A method of differentiating between a Low Pressure and High Pressure fault while still only using one status indicator (flashes when the fault condition = High Pressure).
Next up; redesign of controller PCB.


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