I have a battery tester meter (Mallory) that came from a retail store. The meter is magnetized and now sits center scale, instead of over to the left. Any solutions to return it to it's normal state. I tried reverse polarity- it goes to the left, but then returns to center.
thanks
left.
polarity-
Just wondering--is there a zero-adjust screw or tang (for want of a better word) on the meter?
HankG
Cobblers and rubbish. You've probably dropped it.
Like Hank suggested, should be a flathead screw adjustment on the front of the meter, at the bottom.
left.
polarity-
Sounds more like some kind of mechanical failure, I've never heard of magnetism causing that margin of error.
Dave
Mike Muderick schrieb:
I've seen such an effect when the transparent plastic cover of the scale has been wiped intensively for cleaning purposes generating electrostatic charge. Try to breathe on the plastik to discharge it.
HTH
Reinhard
Magentism won't affect a normal D'Arsonval meter movement as far as zero position is concerned.
If you examine it closely, there will probably be an obvious cause like a bent needle or misadjusted zero screw.
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Tried all of the above. There is no zero-adjust screw. Took the plastic cover off to try and discharge any static electicity. Nothing is bent- meter wasn't dropped- It just won't go back to zero. mm
The
left.
polarity-
Maybe the internal magnet shifted.
Mark Z.
Hi...
It's just a shot in the dark, but doesn't cost anything so perhaps worth a try... ?
Dampen a clean cloth in a bit of diluted fabric softener; wipe the whole thing down with it. See what happens.
Ken
Huh? :)
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Well, since you've already had the cover off, try this. Open the meter again and gently try to move the needle back toward zero with a fingertip or a toothpick. If it doesn't move freely, or moves but stays in the position it was moved to, your meter is damaged. Most likely cause is a broken hairspring or pivot. In either case, the meter is unrepairable by most. The only course of action is to buy a new tester. You can, of course, get some small tools and gingerly disassemble the meter to get at the innards, but if the meter is damaged as I described, you're just chasing a rainbow.
If the meter needle does move freely but just returns to mid scale, you might be able to remedy that. Open the meter and remove the screws that hold the meter's mechanism in the housing. You might have to fiddle with the wires that connect the meter mechanism to the terminals on the rear of the housing. Keep them out of the way, or at least keep the strain off those wires because they attach to a delicate mechanism. On the rear of the movement is another pivot adjustment, normally where one of the connecting wires is soldered. Gently move this pivot arm and see if the needle responds. If so, see if there is enough range in movement to return the needle to normal zero position. If so, you're home free. If not, you're back to square one, looking for a new tester.
-- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "Mike Muderick" wrote in message news:KW2Mf.5967$pE4.4446@trnddc04... > Tried all of the above. There is no zero-adjust screw. Took the plastic > cover off to try and discharge any static electicity. Nothing is bent- > meter wasn't dropped- It just won't go back to zero. > mm > > > "Reinhard Zwirner" wrote in message > news:dtq2cg$p6a$00$1@news.t-online.com... >> Mike Muderick schrieb: >> > >> > I have a battery tester meter (Mallory) that came from a retail store. > The >> > meter is magnetized and now sits center scale, instead of over to the > left. >> > Any solutions to return it to it's normal state. I tried reverse > polarity- >> > it goes to the left, but then returns to center. >> >> I've seen such an effect when the transparent plastic cover of the scale >> has >> been wiped intensively for cleaning purposes generating electrostatic >> charge. >> Try to breathe on the plastik to discharge it. >> >> HTH >> >> Reinhard > >
be
meter's
afree.
Before you change the rear spring setting you should inspect the spiral springs. I have seen cases where the spiral turns got tangled (probably by too much current). I used a tooth pick or small wire to untangle the loops of the spring. Also look at the pivots. If your meter coil and pointer are supported by a "taught band" then all of the advice I gave doesn't apply.
Bill K7NOM
Well, the coil has to react with something. It's been a long time since I've taken a meter movement apart, but clearly at the heart of the meter movement is a magnet. If the magnet is normally stationary, while the meter coil and pointer move with voltage applied, if the magnet were to physically rotate, this would affect the zero center of the coil / pointer, yes?
Mark Z.
Actually, just realized my error. If the coil were magnetized, my point might have been valid, otherwise not.
"never mind"
Mark Z.
Right. :)
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Mike
a =BD scale thing like this is usually a hair spring failure or possible a shock to the spring has caused a coil to interfere with another. Bob AZ
Mike
a =BD scale thing like this is usually a hair spring failure or possible a shock to the spring has caused a coil to interfere with another. Bob AZ
I think you might find that these Mallory cheapo testers actually place a load across the cell under test. The meter may not be a hair spring device at all but more like a car Amp meter.
Chances are good that the meter movement has suffered physical damage, or has had a mechanical part failure.
Damage can be related to harsh handling or misuse. Checking a battery voltage that exceeds the selected range/type can cause irrepairable damage. In many cases, this will open the moving coil windings (fuse action).
I suspect that since the meter will deflect down-scale (as well as up), that the problem is a damaged hairspring. There are almost always 2 hairsprings, which are wound in different directions, at each end of the armature. As each hairspring tension opposes the other, if one were removed or weakened, the other would be stronger, moving the pointer "harder" in that direction.
If the meter movement isn't the moving coil type, then a hairspring or the band has possibly been damaged (weakened or distorted) by overvoltage or misuse.
If the meter wouldn't deflect down-scale, I'd suggest that the problem might be a small bit of debris inside the meter movement that was stopping the coil from returning to it's zero position. Sometimes a small magnet flake or other material will cause this.
Resetting hairsprings is (not can be) a very delicate procedure. Meter manufacturers used to actually list hairsprings as replacment parts. The tension needs to be precisely balanced for a precision meter application. Many armatures also utilize counterweights fitted on pins that extend outward radially.
If it's a separate panel meter (not built into the tester's case), and you can see some numbers on the meter, you may be able to find a suitable replacement meter assembly. Many meter movements have a full scale current value printed on the meter faceplate/scale plate, something similar to 100uA DC F.S. (full scale deflection at 100 microamps). For using meters of different ratings as substitute replacements, refer to books covering meter shunt resistors and similar topics.
Cheers WB ................
Mike Muderick wrote:
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