Flux meters

[Opcom]

being test equipment is part of the ol' hobyy, a TS-15C/AP Fluxmeter was played with. in the late hours last night. just how did people measure the strength of magnets before the hall sensor was available? A mystery, except maybe to some of the scientists around here. I'll describe its workings, in hope that it may benefit someone in their pursuit of AM, perhaps someone making a choke or electromagnet. It measures 1200 to 9600 Gauss. That is 0.12 to 0.96 Tesla.

Running on just one D cell, it has two meters. The D cell is in series with the meters and some resistors and a pot.
(no nonlinear components: diodes, tubes, transistors etc).
One of the meters is special in that its case has no ferrous items and it has a movement that has a very well-oriented N-S pole type structure.
The special meter's 'magnet' is not magnetized but seems to be just a pole piece surrounding the movement coil.
The special meter is use as the probe.
The meter is inserted into the gap and centered mechanically in that space.
The field 'under test' in the gap will either aid or thwart the upscale movement of the needle when a current is passed through the meter's coil.
There is a DPDT polarity reversal switch of the customary arrangement, so that if the meter is inserted against the direction for the test and wants to read towards negative (offscale below "0"), only the switch need be thrown to electrically flip it.
Once the probe meter (that special meter) is positioned, the instrument is turned on and current flows through the special meter and the instrument's reading meter.
The pot is adjusted until the special meter reads full scale, shown as a red mark on the face.
At that point, the instrument meter, in series with the probe meter, will directly indicate some amount of gauss.
It was noted that if there is no field, the probe meter will not deflect.

The principle is that the current needed to move the probe meter's needle a precise amount (from zero to 100%) is governed by the magnetic field in which it is inserted, and that current moves the instrument meter's pointer to a position on its own calibrated and numbered scale representing the strength of the magnetic field being measured.

I hope this was an interesting tidbit. It might be something that could be made at home, and requires no fiddly solid state-oid parts and is not dependent on exactly how good the battery is. My tests were done with a C cell that also happens to fit the battery casing. The value is that it made me think outside of the usual humdrum of high technology. Its simplicity and elegance is a beautiful thing.

Military-scanned manual versions attached. Manuals courtesy of the CECOM military library. Freely sent by e-mail. These are great people and have sent me high resolution scans of any manuals listed on their site which I have asked for, including that 2KW 83 PP amp for use with the BC-610.
Of course these are electronic scans and not the same as buying a nice reproduction paper document, which I often prefer to have in my library when the gear is complex.

[Opcom]

getting timeouts, something on this end?. here is just the basic schematic, enough for understanding. PM for a copy. The images show the meter being used to test seldom seen and top secret WWII Flux Battery prototypes.

[WBear2GCR]

Looks to me like it was intended to measure the rather large gap of a magnetron's magnet?

I have a pair that are not in the best of shape that are meters, center movement, and there is a thin copper tube that appears to have a jewel in the end away from the meter side. About 1/16" tubing, I'd guess. Don't bend it, eh?

One is higher T the other lower...

...not useful for the gaps of speakers though...

             _-_-

[WQ9E]

Among the stuff I inherited from my father is a magnet charging/aging fixture designed to correctly magnetize the pole pieces when rebuilding meter movements.  It has a capacitor bank which is charged and then discharged (via an ignitron) across whatever fixture is needed for a specific pole piece.

There is a big area of specialized knowledge in that area of electronics.

[Opcom]

They are exactly for magnetron magnets. They will work in any gap they will fit into as long as the gap is N-S. The probe part itself looks like it is just over 1/2 inch. Pictures of those made with the copper tubing would be interesting. It's possible these have 'non ferrous' pole pieces. Maybe they do, so to avoid being magnetized. It wasn't well explained, maybe because if the meter was really messed up, a new one would just be ordered. Makes me think, if the poles were removed from a regular meter if that would render it usable for the purpose.

A physically large (3KW) klystron magnet here is apparently too weak to hit the 1200G end of the scale, the lowest reading the meter will make. There are a couple of magnetron magnets around that look like the two in the illustrations but they have to be dug out. They have been stored with improvised keepers in the gaps. magnets are weird. The only things that are preserved by shorting them out.

I'm wondering if I could make it more sensitive by changing something but I don't want to mess it up, and part of the rule is that the probe meter has definite current limits, like any other meter. If the 10 Ohm resistor across it were increased, more of the measured current indicated on the panel meter and going through its own resistors would go through the probe meter making the unit more sensitive. Not worth the risk of damaging the unobtainium probe meter though.

I agree it is a very specialized part of electronics. I wonder by what method magnetic fields in things like toroids and other RF parts (for MF-VHF) are measured? It's one thing to know the current and use Ampere-turns to estimate it, and another to really measure it over a cycle.

I've asked about a probe or manual for this higher tech gaussmeter, which II am right measured DC and RF fields. (no Hall sensors existed then)
http://69.36.164.11/wanted/1009071.jpg
but no one has any data. One of these meters is for sale sans manual from an instrument company and it isn't cheap.

About magnetizing those meter pole pieces, that seems similar to a recent product for killing hard drives removed from equipment. They are thrown down a somewhat form filling rectangular chute and an optical trigger discharges a cap bank through a coil around the chute as they pass though the coil zone, wiping everything. So it is claimed.

[WBear2GCR]

Patrick, per your interest, pix.

The two are different ranges, fwiw.

[Opcom]

That's great! My magnetron magnets are a bit low on the scale, but there are two more to dig out and test. I'm disappointed in the huge klystron magnet being <1200G. I hoped it would be more because it has a decent size gap. I suppose magnets 'wear out' over time especially if not stored with a keeper.

[WBear2GCR]

I think that they were typically 2T.
Alnico does lose magnetism. But the good part is that they can be recharged.
So, next you have to get urself or build a magnetizer!

             _-_-

[W7TFO]

I have sent vintage Altec speakers to Great Plains Audio in OK (The authorized manufacturing and repair facility for all things Altec Lansing), and they regularly re-magnetize the alnico magnets in the old stuff as part of a complete rebuild.

73DG