? Meter to test thermoelectric potential of unknown metal

What happened to the broken meter?

Do you have it in hand? Unless this twigs somebody's memory, you might want to post some high-res photos of the device. It sounds like it's working on the electrochemical potential of the metals.

Why do you think the meter isn't repairable? Is the movement totally destroyed? I've managed to fix some analog meter movements that looked pretty busted up. Is it taut-band or jeweled?

Best regards, Spehro Pefhany

Ok its taut-band and the taut-band is broken or melted or something. So to repair this meter I would have to replace the taut-band and I think that is beyond my ability and equipment. A replacement meter would probably be less expensive than paying someone to repair this one.

I have been looking for a shop that repairs this type meter but so far I have only one possible candidate. This time Google has not been my friend :-)

BTW I have repaired sticky meters and such in the past. Bill K7NOM

If they still have the probes, why don't you get your hands on an old thermocouple meter like this one on ebay:

Connect the probes to it and play around with a couple of known metals. With that info, plus consulting an electrochemical potential table, it should be easy to "calibrate" the meter.

HTH,

Jeff

Hey, isn't this the kind of function you were talking about, the text says, "Sorts alloy scrap, verifies parts in receiving, inspection for proper alloys."

HTH,

Jeff

Chances are that it's a standard meter movement, so you just have to figure out what the sensitivity is (and maybe the internal resistance). If there are some electronics driving it, it would likely be non-critical 1mA movement or something like that (much lower current and it compromises robustness).

Why don't you crack it open and have a look? You can sub a digital meter and stick it on some known metal for the purpose of getting an idea of the sensitivity.

Best regards, Spehro Pefhany

This is a pure guess based on zero evidence!

If I've guessed the right system it's the electrodes that are special and the meter's pretty standard. I would expect one electrode to be a solid metal contact and the other to be some sort of electrolyte pad - perhaps a bit like a Q-tip dunked in saline solution.

Dependent on the contact potential of the test metal this "battery" will develop up to about a volt with a source impedance of tens or hundreds of ohms. A a typical 1mA 100ohm meter should be OK with enough series resistance added to bring it down to the same sensitivity as the original meter.

As a very long shot - are you sure the meter's dud? A completely dried out electrode pad would also give nil reading.

Jim

This link seems to be busted. I pasted the full link below, but it will need some splicing:

Interesting looking gadget, but not cheap.

Doug White

Thanks, that was the type of information I was looking for. I don't think my friend will be happy with that price however.

The existing meter is just a sensitive meter with some test leads. I can't test the meter sensitivity because of the broken pivot (taut-band) The meter is 7 inches wide so finding another movement will be difficult, I think.

Thanks for the help Bill K7NOM

Hi, Bill. I don't think the current goes through the band. It is just a spring fastened to the indicator, instead of using a shaft with jewel bearings, etc. The coils should still be ok, unless the band is gone because someone put the meter on a 12 volt storage battery and ran so much current throught the meter that the shock also took out the band.

Do you have access to some sensetive meters? Most hams have one or two in a junk box somewhere. Try substituting a 100 microamp meter and see if the thing will give any indication. Also try a digital multimeter using the lower current ranges as a substutute meter movement. It won't care how it's wired or minimally overloaded a bit.

Sounds like a good weekend project!

Good luck, Paul KD7HB

Hmm, it appeared busted to you? I wonder if that's got anything to do with something I read in the business section of the Boston Globe within the last couple of days about a couple of the upper eschelon internet "backbone" data carriers who are having some sort of hissy catfight? The article said that could possibly disrupt internet communications between parts of the web in different geographic areas.

I checked that tinyurl before I posted it, and it worked. I always do that, because of my long standing anality about hating to be cought in a mistake by anyone other than myself. :-)

I checked just now and that tinyurl still worked fine from here in Red Sox country, where we're in mourning for the next week.

That's what I thought too. Looking at its two replacement "probes" (at $500 EACH) I gather that one is a Peltier thermoelectrically cooled plate and the other one is a heated probe. I'm assuming that's done to magnify the thermoelectric potential effect, to make it easier to distinguish between different alloys in the same metal "family". Anyone here able to confirm my speculation?

Jeff

I live near Boston, and although it didn't work this morning, the link seems to be OK now. I don't know exactly how tinyurl works, but they may have had a temprorary hiccup.

Doug White

Yeah, me too. And IIRC, it wasn't a 404 message, but something really weird. Bob

[ ... ]

[ ... ]

Hmm ... I hadn't heard of that problem. Looking at the internet health report, the only thing a bit slow at the moment is my (current) ISP talking to itself. :-)

It worked for me -- enough to scare me at the price for that otherwise desirable gadget. :-)

Sorry about that.

Enjoy, DoN.

Might be a simple - return to be fixed for a repair charge.... Might have to sweat talk with some options or goodies...

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder

Bill Janssen wrote:

I would need a Time Machine to go back in time to the era that the company still existed

Bill K7NOM

applied

seriously

another.

I would also assume it measures thermoelectric voltage. I have a meter at work that connects directly to a T type thermocouple. If it has the meter movement sensitivity printed anywhere I'll let you know. Your meter face may also have it but sometimes you can't see it unless you look pretty hard...

If it's a straight connection to the movement, it may show both a current and the internal resistance (eg. 50uA/500 ohms), and in the case of a thermocouple meter like yours, it may have a presumed resistance value for the total thermocouple circuit (eg. 10 ohms).

Best regards, Spehro Pefhany