TORQUE
AND ITS TYPES
Torque is defined as the twisting force. The twisting force
is experienced due to magnetic field.
*Torque is denoted by “Ï„”
Ï„ = F *
d
where F = force due to magnets (magnetic
force)
d = distance between magnets.
Mechanism:
Consider two permanent magnets with north
pole and south pole, now in between the magnets place an electromagnetic
substance by suspending with a thread. When this electromagnetic is energized, due to presence of permanent magnetic there is attraction between them, so the
flux transfers from north pole to south pole. Due to this flux there is
twisting movement in the electromagnetic substance, this twisting movement is
named as torque. Observe the below figure for idea view.
* The figure in left side shows no deflection in electromagnet due to absence of torque when supply is not given, once supply is given the torque deflects the electromagnet as shown in right side figure
* The figure in left side shows no deflection in electromagnet due to absence of torque when supply is not given, once supply is given the torque deflects the electromagnet as shown in right side figure
i) Deflecting torque (Td):
When an instrument is
fed with supply, the magnets takes their active position and leads to formation
of magnetic fields. This magnetic field produces a twisting force. This force
indicates the value of electricity through pointer on the indicating scale.
ii) Controlling torque(Tc):
The torque which is used
for controlling. In deflecting torque(Td) the pointer moves indefinitely and
independent of the value of electrical quantity. To avoid this the controlling
torque provides an opposing force to it hence the pointer is to under control
and measures accurate.
The functions of controlling torque:
1.
Increases the deflecting of moving system by opposing deflection
2.
The position of pointer is under zero when deflecting torque is
removed
*
This controlling torque is provided by string (or) gravity. Spring is made of
Phosphor-bronze is attached to the moving system which controls Td by twisting
in opposite direction.
iii) Damping torque:
When an measuring instrument fed
with the supply the moving system acted upon by deflecting due to inertia will
oscillates about the final position before coming to rest. These oscillations
are must be eliminated. To avoid oscillation damp torque is provided which
opposes the pointer movement and operates when system is moving.
*The
degree of damping decides the behavior of moving system i.e. we have to
consider three types of dampings shown below:
*At
under damped position the pointer will oscillates and comes to rest after some
time.
*At
over damped condition the pointer will become slow.
Dead beat:
The degree of damping is adjusted to certain value that the pointer moves and
quickly comes to its final position, the instrument is said to be dead beat.
*Air
friction, eddy currents and fluid friction are the production of damping force.
*The below
table shows the instruments and their effects in mechanism
|
EFFECTS
|
INSTRUMENTS
|
|
Magnetic effect
|
Ammeters, Voltmeters
|
|
Thermal effect
|
Ammeters, Voltmeters
|
|
Electrostatic effect
|
Voltmeters
|
|
Electro dynamic effect
|
Ammeters, Voltmeters, Wattmeter
|
|
Electro magnetic effect
|
Ammeters, Voltmeters, Wattmeter,
Watt-hour
|
|
Chemical effects
|
For DC Ammeter-hour
|
No comments:
Post a Comment