The
d’Arsonval meter movement has a small, rectangular coil of wire. The coil is
suspended in a magnetic field created by a permanent magnet. When current is
applied to the coil, it becomes an electromagnet.
Before you
use a meter, check its instruction manual. Each meter is a little different and
you should be aware of any important instructions in the instruction manual.
The
energized coil then lines up with the poles of the permanent magnet. The amount
of current applied to the coil controls its movement. An electromagnet that is
free to move will align its axis with the magnetic axis of a fixed magnet.
The coil
must be free to rotate in order to align itself with the magnetic axis. The
coil in the meter is mounted on pivots that permit easy rotation.
Two small springs
are mounted on the top and bottom. These springs offer slight resistance to the
rotation of the coil. The springs control the position of the coil when there
is no current flowing.
When current
flows in the coil, it produces a magnetic field around the coil. This magnetic
flux overcomes the force of the springs and moves the coil.
A pointer on
top of the coil rotates to mark the amount of movement. The greater the current
through the coil, the more it turns, and the further the pointer moves. The pointer
then stops in front of a marked scale on the face of the meter.
As you look
closer at the d’Arsonval meter movement, you will find that it can be extremely
sensitive to small currents. For instance, a relatively inexpensive meter can
give a full-scale deflection of 10 microamperes (A).
Full-scale
deflection is the total range of a meter scale. A microampere is one-millionth
(0.000001) of an ampere.
Meter
deflection is determined by three factors:
1. The
number of turns of wire in the coil and the amount of current flowing in the
coil.
2. The
strength of the magnetic field produced by the permanent magnet affects the
positioning of the coil.
3. The
tension of the springs and the friction of the bearings determine the sensitivity
of the meter movement. The amount of current flowing through the meter
determines its pointer deflection since it is the only variable in the meter
movement circuit.
The scale of
the meter is calibrated (marked) to show the type of reading (volts, ohms, or amperes).
No comments:
Post a Comment