Analogue meter - suspension repair
N_Cook
phosphor-bronze ribbon suspension , not hairspring and jewels. A ribbon, top
and bottom, holds the coil frame and passes current. Each ribbon is soldered
to the frame then passes through a hole in the offset-rotatable anchor ,
passes over the rounded edge of an open end of a U-shape of manageable size
phosphor bronze spring , and soldered along the arm of that spring. The
solder point to the frame has failed from a jar / knock. So both U springs
are now opened to a V in comparison. I have tried solder to the end of the
fine ribbon and the stub on the frame, both take solder fine but not joined
up yet. There is enough length of fine ribbon on the broken side to resolder
to the coil frame , pass thru the hole and anchor off , on its u-spring
anchor farther along than originally.
But how to bring the open-U springs back to proper U before soldering the
anchor point. A matter of making a jig to compress or some sort of external
spring over them ? And of course I've not seen a functioning movement. I'm
assuming setting up as U and then opening out a bit with the jigs removed,
or would the jig need to compress to more than U and then open out to U with
jigs removed, normal use.
Pushing down on the spring of the good end and letting the coil frame drop,
with gravity, it seems to be centrally aligned over the pole piece, when
the spring is a proper U viewed on side.
Where would one find , even robbing, short lengths of such rbbon if it was
required?
Arfa Daily
"N_Cook" <div...@tcp.co.uk> wrote in message
news:ipltei$n6j$1...@dont-email.me...
A couple of years back, a colleague gave me a professional Ferrograph audio
test set. This has a large format precision meter on the front, which has
the same vertical 'twisty' ribbon as the coil / needle suspension scheme. It
was broken when I got it. As there was little chance of being able to get a
replacement movement, I figured that repair was worth a go. As I recall
(it's been a while ago now) I simply fed the wire back through the hole in
the U-frame and held the frame in tension pushing down on pointy tweezers in
one hand, whilst using the soldering iron in the other hand. I had
pre-tinned both the wire and the frame, and simply bent the end of the wire
over with the tip of the iron, whilst letting a small 'blob' of solder
previously fed onto the iron's tip, flow into the joint. I was absolutely
amazed when I let go of it all, and blew on the pointer. It went from one
end of the scale to the other, as smooth as you like. No issues with
centreing or sensitivity or whatever. I seem to think that I struggled
slightly to get a good zeroing action from the zero offsetting screw in the
perspex cover, but I did manage it in the end. I can't remember why, or how
I got it to zero in the end, but I did, and it has remained correct since.
The unit is in daily use, so it has been an effective and long-lasting
repair.
Make no mistake, it was a delicate and fiddly procedure, with lots of
holding of breath and magnifying glasses and so on, but quite do-able for
the likes of you who enjoys challenges like this. Go for it. You've nothing
to lose.
Arfa
N_Cook
news:ZWvvp.43321$o81....@newsfe28.ams2...
Likewise no chance of a replacement . Reminds me Test Instrument Services,
Totton Hampshire no longer seem to do this and meter rewinds , keeping
ancient ship-bourne engine/generator monitoring meters of the world's
merchant ships going
Certainly a job fully under a x4 or so illuminated inspection lens. This
Sifam one you can rotate suspension anchors at either end , but there is no
user accessible adjustment of zero once the meter scale is set in the
housing.
I think the sensible route would be . A loop of copper wire around each U
spring and twisted ends until parallel spring arms. Offer up the ribbon and
solder up and then while a finger over each spring, in turn, cut the copper
wires and gently release finger pressure. I'd rather have too little tension
in the U sptrings and so the fine ribbon, than too tight.
Wild_Bill
though what has been described is likely to be the Taut-Band type of meter
movement.
--
Cheers,
WB
.............
"N_Cook" <div...@tcp.co.uk> wrote in message
news:ipltei$n6j$1...@dont-email.me...
N_Cook
news:lZxvp.82671$of7....@en-nntp-15.dc1.easynews.com...
I never looked inside one but all those broken Pye/Cambridge? moving spot
galvanometers presumably had that system. While at it anyone know what the
suspension is in Megger insulation tester? that dead springless movement,
jewelled without hairspring? - I've never looked insiside the meter movement
of one
Markus Faust
First try to attach the ribbon to the frame. You might want to remove
the magnet first (if it isn't a core magnet type meter).
Remove the solder from the U-spring, especially near the open end with
solder sucking wick.
You have to press down the spring at the broken side more than the final
position so it will pull the other side into position one it's released.
You have to try that out. Too few tension is just as bad as too much
tension, because the frame wouldn't be in the right position then.
Solder the ribbon to the U spring near the turn of the U. Release the
spring, check if the tension is right (axial position of the frame). If
it is, you can now slightly adjust the axis of the frame now by pushing
the ribbon left or right. Now fix the ribbon near the open end of the
U-spring. Check that the pointer moves smoothly over the whole range by
slightly blowing at it.
Re-attach the magnet/scale (if removed).
Check equilibration (set the pointer to about 25% of the range and check
that it doesn't move when the meter is tilted back/forth; repeat for 75%).
Set the pointer to zero. Check sensitivity. If you can adjust
sensitivity at the electronics, do so. Else you have to move the
magnetic shunt (small iron strip at the magnet) to adjust sensitivity.
Markus
Shaun
"N_Cook" wrote in message news:ipmgml$5sn$1...@dont-email.me...
I used to work on meter movements from time to time. Some of the Meggers I
worked on had a dual coil which worked as a balance (between currents in
each coil). One or both of the jewels had a spring under them, I remember
putting the coil assembly carefully back into the jewels just with a pair of
tweezers.
Shaun
N_Cook
news:JYgwp.18468$uh5....@newsfe02.iad...
2 , 3 or 4 conductor wires going to the coils frame?
2 hairsprings in opposistion ? why not no springs
Shaun
"N_Cook" wrote in message news:iptijd$vqn$1...@dont-email.me...
I don't remember, it was 13 to 17 years ago that I did that type of work.
Shaun
jeff_wisnia
<snipped>
> Make no mistake, it was a delicate and fiddly procedure, with lots of
> holding of breath and magnifying glasses and so on, but quite do-able
> for the likes of you who enjoys challenges like this. Go for it. You've
> nothing to lose.
But your temper.....
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.