Photoluminescence Spectra of Emeralds from Colombia, Afghanistan, and Zambia by Brian Thompson. See Research Below
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 Post subject: Possible setup for angle measurement
PostPosted: Tue Jan 31, 2017 2:26 am 
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Location: Wylie Texas but in Alaska for a while
I came across some parts at my dads place that may let me make a display for angles

PARTS I have:
1) An LFE Percent panel meter that is 00.00% at 1v and 100% at 5v. It has a 4 ½ didgit display.
2) A .1% PERCISION POT. Unfortunately it is a 10 turn pot and a little bit larger than I would likie, but I have it
3) Some 200 ohm 10 turn pots.
4) Some lm 317 adjustable voltage regulators. These normally adjust voltage from 1.2 to 30 volts.


I ran some excel spread sheet models based on the voltage regulator designs and have a successful model that gets me 1.37 volts to 5.37 volts.

The design only requires:
- The LFE percent meter
- A 317 coltage regulator
- A fixed resistor (I am going to use the 200 ohm 10 turn pot for this one)
- The precision pot
- They recommend 2 caps I may have some that will do. But the circuit will work without it.


I have a design for a voltage regulator that that can get me down to 1 volt, but it requires additional components and a negative voltage supply

I also contacted the LFE company. There are two adjustments to calibrate the gage, one is for offset the other is for span.

I believe that I can get a prototype working in the next few weeks, that will let me test how much span I can adjust.

I can also make a test setup to check for repeatability.

I also believe that this meter will show some negative percent, so I should be able to see how much past 0 I go. That will be a nice feature.


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 Post subject: Re: Possible setup for angle measurement
PostPosted: Tue Jan 31, 2017 11:39 am 
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Precision pot. What's the Linearity?

Forget using ten turn pots. 1/40 the resolution. You are really only using one quadrant of one turn.

Here's a general clue page. Once you get beyond the rant on it, there is a block diagram that will be helpful. (I was furious when I wrote that page.).

http://www.gearloose.com/no.html

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 Post subject: Re: Possible setup for angle measurement
PostPosted: Wed Feb 01, 2017 2:55 pm 
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Gearloose wrote:
Precision pot. What's the Linearity?

Forget using ten turn pots. 1/40 the resolution. You are really only using one quadrant of one turn.

Here's a general clue page. Once you get beyond the rant on it, there is a block diagram that will be helpful. (I was furious when I wrote that page.).

http://www.gearloose.com/no.html


it is a .1% linearity

I know that it is not the avery good solution, but it is a 20000 pot. I checked it with an ohm meter, I get 2000 per turn. or 555 in 100 degrees. I know that this is low, but I ran an excel spread sheet and I can get right at 1.37 to 5.37 volts if I get the secnd resistor low enough, and use the very first turn of the pot.

It is not what I want to use for the real thing, but it was in the drawer and I have it. So I can make up a circuite and at least see how much span I can adjst on the meter.

Dad taught EE for 40 years, and collected various parts over the years. These are just ones that I down when I was down there and was able to grab on a first qick pass. I did not have room for the scope, precision power supplie(s) and the rest of his collection.


we have an apoitment today with the surgeon to talk abut the stim implant for my daughter. I hope to have some idea of when I will be getting back o Dallas after that. BUT I suspect that we will have to wait for additional tests. They are also releasing a new smaller battery for this model, by region, so I am not surewhen it is going to be available up here.

anyhow, I hope to at least get a prototype working and see what I have.

I will look at the link you gave.

At first I hoped that the meter I picked up ws a 0-5 volt meter. But it is set up fpr process automation and gives a percent reading from 1-5. That may actually work out.

I tried to model various voltage dividers to get that range, but I was having problems getting a set of resistors that worked.

The whole thing may not work, and I am prepared for that.

I also brought back an old surveying instrument. I brought pictures of it onto some people who thought it might be used for mine surverying. It has several angle scales with venires. I may have to do a little work to clean up the silvering and get the dark lines back, but if I can get the meter working, I should be able to set it up and check the reading out to what shold be a pretty good master for measuring the angle. But it will take a while. I am a long way from actually building a machine =that would need it. Right now it is more of an experiment to try and see if the concept is going to work, and if I can get the precision.

I also know that if I cannot get it with the pots I have, I can get more suitable ones. But the price of this test is just my time. It will take a while o find all of the goodies that dad had put away. There are 2 barns and 3 storage rooms. His place is also a 10 hour drive from my home. So it will be a long time before I get to go through it. That assumes that other folks do not berak in and start carting things off.

I jut reviewed the page you linked to. Maybe I will come across a 0-2 volt meter on another shelf and some nice 5k pots. I did come across a set of other 10 turn trim pots, but they are only 200 ohms. I plan to use one of them for the prototype, according to the excel spread sheet, I need 168 ohms to get the 1-5 volts.

Who knows maybe I will come acroos a 0-2 volt meter at dads. I think that there were 5 or 6 meters there.


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 Post subject: Re: Possible setup for angle measurement
PostPosted: Wed Feb 01, 2017 5:50 pm 
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After looking at the diagram from gearloose, I rechecked the voltage divider spreadsheet I made up.

I found an error in the formulas.

I did the calculation assuming a 100 degree arc, to equate to 100%

I also set the starting ohms within the range that I could measure on the pot.

I know that the 10 turn pot is not what I need, but it is what I have. After fixing the spreadsheet, it looks like I can get 1.00 to 4.92 volt range using just a voltage divider and 5 volt regulated supply. I have some 5 volt regulators in the chips I picked up from dad. I should be able adjust the span to accommodate this range.

I believe that the panel meter I have is pretty good quality. IT gives me something to tinker with.


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 Post subject: Re: Possible setup for angle measurement
PostPosted: Wed Feb 01, 2017 6:50 pm 
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Nothing matters if you use a 10 turn pot. You will just get empty magnification. The resolution span just isn't there. The pot's resolution should be better than the DAC's. This is like taking a ruler and using only 1 inch of it and trying to measure a hair by using a magnifying glass. A lot of people have tried this..they gravitate to 10 turn pot, and it's wrong.

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 Post subject: Re: Possible setup for angle measurement
PostPosted: Wed Feb 01, 2017 11:27 pm 
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Gearloose wrote:
Nothing matters if you use a 10 turn pot. You will just get empty magnification. The resolution span just isn't there. The pot's resolution should be better than the DAC's. This is like taking a ruler and using only 1 inch of it and trying to measure a hair by using a magnifying glass. A lot of people have tried this..they gravitate to 10 turn pot, and it's wrong.


I agree that I do not get the span that would give me the resolution I want.

It is also much bigger than is practical.
But at least I can do a prototype and see how much adjustment I can make on the meter for both span and offset.

I plan to use a single turn pot when I make the machine.


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 Post subject: Re: Possible setup for angle measurement
PostPosted: Thu Feb 02, 2017 8:56 pm 
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I was glancing through some sales for the Ardinuo projects and I saw they now have a 240x320 display panel unit and of course the modules have processors and sensor inputs galore. As anyone seen any articles about uing one as the basis of a faceting machine angle indicator? They have schematics and helpful hints and forums and the programming is linux derivation OS. They have internet as well as Wi-FI communication modules. Love to see faceting diagrams exchanged :) Hoping someone has already moved in this direction . Jim


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 Post subject: Re: Possible setup for angle measurement
PostPosted: Fri Feb 03, 2017 5:23 pm 
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Chapter 20 (Volume 2) of the Tom Herbst Faceting books has an excellent write-up on constructing an Arduino-based angle indicator.

Keith


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 Post subject: Re: Possible setup for angle measurement
PostPosted: Fri Feb 03, 2017 5:43 pm 
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Thanks, I have that book, but haven't read that far :) Duh! Jim


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