Viscometer board proceeding, some RS232 fun.

  Well, things have been proceeding apace, and I’m feeling pretty confident that I’ll have both versions done fairly soon. For debugging the device I’ve decided to create a kind of terminal, this allows one to directly access commands and see log information from a terminal program. This is handy for seeing data over time and for various other uses.
 
Here are some pictures…
 


Prototype viscometer board out futher
Prototype viscometer board out futher

Prototype viscometer board
Prototype viscometer board

The early output of the sample terminal. I have created a kind of console, I will implement commands as they are created.
The early output of the sample terminal. I have created a kind of console, I will implement commands as they are created.

 
I think this is going to turn out well.

Getting closer to final completion

A long road behind and still some ahead, here are some pic of the viscometer in its state of completion.

stormer viscometer with cover looking in
stormer viscometer with cover looking in

viscometer from the back
viscometer from the back

viscometer standing up
viscometer standing up

viscometer laying down
viscometer laying down

stormer viscometer with cover
stormer viscometer with cover

Now to implement the ModBUS protocol and finish up this project.

In-Process Stormer Viscometer – Damn near complete

  The viscometer is nearing full completion! YAY! To mark this occasion to mark the end of a long two years, I am placing a small gallery of the almost finished product. The only thing missing is the outside cover which consists of a 4″ od aluminum tube. Also, the springs I’ve ordered have also not arrived as yet, however, for now, the elastics will suffice. Here are some of the features and facts:
 

  • Can be used in-lab or in-process
  • Selectable RPM with a tight tolerance on RPM +/-0.5RPM
  • User calibration routines. This allows the end user to calibrate with 3 fluids of known viscosity
  • 16 key keypad, used for calibration and settings, also for running special tests
  • Can be used as a laboratory gel-timer
  • Can be used for custom tests besides stormer viscometry
  • Low power consumption <100ma or <2.4W
  • RS-485 Serial output
  • Control electronics have complete galvanic isolation
  • 24VDC supply required
  • repeatability (requires further testing) +/- 1.5%
  • Modbus protocol (not yet implemented)
       
      Here’s the Gallery!

       
       Yes, a few too many pictures, oh well.
       
       This thing took me quite a while and what I learned from it was immeasurable. Thankfully now that everything works as expected I can focus on my other projects without having this thing hanging over my head. Here’s to completion!
       
      As an aside, here’s an interesting document on viscosity.
      here

New Viscometer board design and physical revamp.

Since my design was accepted in terms of moving ahead on a prototype, I’ve been working first on the board design. I have decided to abandon the PIC18F2620 in favour of the 18F4685. The reason for this change over is due to the fact that the 18f2620 doesn’t have enough I/O to handle the addition of two analog channels and four I/O for RS-485 communication.

This post is more for my own edification and to help me sort out my thoughts on this issue. I suppose for the sake of following my train of thought while sitting here, I’ll outline the specifications, as I think of them.

Overall feature set:
PWM output for 6-24V DC motor.
RS-485 Out – Rec enabled
LCD out
16 key keypad in
2 temperature sensors
LED indicators for power/error
Serial out for RS-232
Input for external reflection sensor
2 inputs for timing sensors

So, thats 1+4+6+8+2+2+1+1+2 = 27 inputs

I found some nice Molex headers that are single row, .100 pitch and is latched. Typically I use the friction based header and housings but it needs to be secure inside the housing and thus I’m trying out the new set. Also I’m going to use vertical out terminal blocks in order to save space inside the unit but not necessarily on the board.

I’m also considering adding an RS-232 port along side the board.

Hopefully this will be the final hurrah!