If the bare meter movement is showing a loss of sensitivity, my
first guess would be a weakening field magnet. It would be a
bit unusual for a modern instrument, however....

Pete


Thank you for your suggestion.

After completely disassembling the multimeter, I got access to the front spring
of the movement and noted that first turn had just overlapped the spring binding
post, possibly due to a shock. Just touching the spring, it went back to normal
with no deformation at all. Now the full scale current is exactly what it should
be.

What amazes me is that I could not find any visible adjustment point (e.g. a
variable magnetic shunt). Evidently they were able to produce very precise
meters requiring no adjustment.

73

Tony I0JX

"Antonio Vernucci" wrote in message
. ..

What amazes me is that I could not find any visible adjustment point (e.g.
a variable magnetic shunt). Evidently they were able to produce very
precise meters requiring no adjustment.


Good find. Better quality meters were rated to 1 or 2 percent at FULL SCALE.
Also, many are rated for mounting on a steel panel. Many are not so rated.
The presence of external magnetic fields WILL affect the reading.

Sometimes you just have to go with the real meter indication and re-mark the
scale to the correct numbers.
I've done that a number of times, it shows the non-linearity of lesser
quality meters.

The presence of external magnetic fields WILL affect the reading.

And don't forget the static charge on the plastic or glass face after you
spotlessly clean and polish it. A little spit may help.

Paul P

bw wrote:
"Antonio Vernucci" wrote
What amazes me is that I could not find any visible adjustment point (e.g.
a variable magnetic shunt). Evidently they were able to produce very
precise meters requiring no adjustment.

"bn" wrote
Good find. Better quality meters were rated to 1 or 2 percent at FULL SCALE.
Also, many are rated for mounting on a steel panel. Many are not so rated.
The presence of external magnetic fields WILL affect the reading. snip


Hi,
I picked up a Weston type 301 5mA d.c. meter marked for use
with a 1/8" steel panel.
I find it takes about 6.1 mA to deflect to full scale
without a panel. That sounds as if the presence
of a surrounding steel panel would increase the meter sensitivity
by about 20 percent.
Could someone explain this, please?

Thanks,
Ed Knobloch