Moving coil meter-How to make new scale??

[Diabolical Artificer]

How do you make a new scale for a moving coil meter? I've tried taking a picture and pasting it to MS Paint, but cannot get the "drawing" the right size. All I was able to do was get it roughly about the right size and then very roughly erase the figures, IE 0,100,200 etc. It looked awful.

I then tried doing it by hand which wasn't too bad,but wasn't accurate. I've forgotten my basic geometry,EG how to find the radius/angle of the scale within the outer meters circle.

Looked online but despite several searches was unable to find anything. The "how to use MS paint" tutorials seem to be using a different version to mine. All I have is a colour bar at the bottom, a toolbox-pencil etc and file, edit etc at the top. To get the outer circumference of your circle for instance can't be down in inches but only in pixels.

Any help/advice most welcome, Andy.

[Dekatron]

You can download Galva, please read the license, on the webpage here: http://www.f5bu.fr/wp/?page_id=13

I can probably do what you want but it takes some time to learn. I recommend that you do the exercises with the included scales to see how it works and also to save with different files names often as it sometimes crashes.

It is a very good software in my opinion.

/Martin

I remember a long time ago rubbing off the old writing with the end of a chewed match stuck in Vim and then using Letraset. Don't re-chew the match when it wears out, false economy (and it tastes awful), use a new one!

[David G4EBT]

Don't know if you have any editing software such as 'Photoshop Elements', but if so, one option would be to carefully remove the existing dial, scan it, then edit it in Photoshop. You could erase the existing numbers, then choose a suitable font, font size and colour, and move and rotate the numbers to place them exactly where you want them. You can then re-size the meter dial to exactly the size that you need.

That's what I did to re-scale the dial on the meter that I used for the homebrew FET millivoltmeter in the pic below. When I was happy with it, I printed it onto photo paper and stuck it on the reverse side of the meter plate. I'm happy with the end result. The meter movement is 100uA and the dial is 6" x 4". It was ex equipment and the wording and numbering meant that as the dial stood, it was no use as I wanted two scales - 0-50 & 0-100, so I erased all the lettering and numbers in Photoshop Elements then added my own numbers.

Whenever I draw anything in MS PAINT I resize in in Photoshop.

Hope that helps a bit Andy.

[FrankB]

I make a tracing or photocopy of the original meter face. Then I turn the meter face over and paint the back the color I want.
I can then modify the tracing / photocopy of the meter face and either glue the tracing to the meter face or copy it using carbon paper to the reversed meter face.
Rub on letters and numbers work well too.

Then spray with a clear art fixative such as Krylon Clear spray.

This has the advantage of leaving the original face intact in case I junk the project and need to re-use the meter again. Also on Weston brand ( and other) meters, they list the type on the face ie: "Type 301", so you can easily look up the meter resistance or FS deflection.

[Mike Phelan]

Andy,

I use the internet version of MS Paint - it's still free and similar to Windows Paint but allows more features.

You can make a new scale and resize it to fit exactly.

HTH.

[Bazz4CQJ]

Check out "Meter Basic" which is the free, limited version of Meter by Tonne, but quite useful. I think the full prog is ~£30, but it produces fantastic results and is always on my Christmas wish list.

B

[Diabolical Artificer]

Thanks all for your help. Basically I need to make the dial read 300v instead of 600v. I've used a fixed resistor and then a preset to "calibrate" it. I drew one by hand but the end result wasn't brilliant- see pic . I will have another go using your suggestions. Finding the needle pivot centre is the tricky bit, but once found that gives you your arc.

I found Power Paint Mike, but need to put some time into it. I also looked for a free CAD download. I'll see if I can get hold of Photoshop too;my Dad uses it, therefor it should be easy to use.

It has "type" # - M25 on it Frank as you say.

Andy.

[daviddeakin]

I would scan it rather than photograph it. Then edit.

[David G4EBT]

Are you seeking to do something like the pic below Andy?

It's not brilliant because all I could do of course was to save the low resolution pic in your post, then to edit it in Photoshop to remove the unwanted numbers and the 'DC Milliameters' text, add the new Voltage numbers, then clean up the rest of the dial a little, leaving the original 'D.C.VOLTS' text in place. (Any of the other text if unwanted could be removed). The forum software will have re-sized the pic and reduced the resolution still further when I uploaded it.

If you have a scanner, I think your best bet would be to scan the existing dial at high resolution, then to save it using whatever photo-editing software you might have, or failing that, to copy it, print it off and post it to someone who can scan it in and edit it to suit. It could then be printed off on photo-paper - either glossy or satin and cut out to be stuck to the rear of the dial.

The problem with all CAD programs is the learning curve. In that regard, I'm not very far up the food chain, but if you don't get a better offer I can fumble around in Photoshop and Paint produce something like the attached pic. Happy to help in any way I can, but if you are wanting a brand new dial creating using a meter dial program, I'm not your man!

[Nymrod121]

Hi Andy
Is the attached of any help as a template? (PM me if you want the slightly higher resolution version - it's only a 61KB jpg file).

Some measurements made (best guesstimate at interpolating ruler scale here):

Movement pivot point = 46.5 mm from top edge (excluding screw fixing tabs)
Scale depth ('0-150' line - '0-15' line) = 2.0 mm
Movement pivot point = 32.5 mm from inner scale line, 34.5 mm from outer scale line
FSD deflection angle = 90 degs.

Best wishes
Guy

[Nymrod121]

Edited image plus dimensional correction:

Movement pivot point = 45.5 mm from top edge (excluding screw fixing tabs)
Scale depth ('0-150' line - '0-15' line) = 2.0 mm
Movement pivot point = 31 mm from inner scale line, 33 mm from outer scale line
FSD deflection angle = 90 degs.

Best wishes
Guy

[GMB]

I make meter scales using PostScript.
Effectively a program to generate the required scaling.

Photo shows an example of a device I built.
Because I was going to show this to the local ham club I decided to make it more nice than necessary so did a full calibration of all its features and then used the calibration data to create the very non-linear scales using PostScript.

It then just comes down to the quality of your printer as the PostScript itself is vector graphics so is infinitely scalable.

I also use this method to do front panels, and in this case some extra correction data charts to go on the side. See the PDF.

[Nymrod121]

That's really good, GMB

[pmmunro]

Andy,

Is this any use to you? I drew it from measurements taken from your photograph and assumed a scaleplate diameter of 3 inches; it can of course be scaled to any other size as you need. To get the required scale you would probably be best measuring the actual scaleplate diameter or the width of the slot at the bottom with a vernier or digital caliper.

Now we have it as a vector file (I drew it in Autocad) any changes should be fairly easy.

It looks to me as though the original was hand lettered and probably the radial scale lines may have been hand drawn during calibration. This is more accurate than just drawing an exactly linear scale based on simple geometry.

If this drawing is accurate enough for your needs then it can be used as it is, printed onto a suitable medium, or I can easily send you a copy with just the arcs and you could rule in the radial lines yourself.

PMM

[Phil G4SPZ]

It looks like you've already got what you need, Andy! For what it's worth, I have had some success in the past using the "scan - edit in MS Paint - print on photo paper" method.

[majoconz]

I would scan it rather than photograph it. Then edit.

+1
Just make sure that you measure the scale accurately, then do a few dummy runs when you print it out after modifying to make sure you get the size right in both dimensions. I scanned and reprinted the dial scale for a Sony CFR-5090 and it all worked out well - a local printshop had a selection of thicker plastic 'paper' and did a great job of printing the scale on that and still the panel light shines through it!