FIELD OF THE INVENTION
The present invention relates to an improved device for mounting both speed
switch and a tachometer simultaneously at the non-driving end of large rating AC
Induction motors. More particularly, the invention relates to an improved device
for mounting a speed switch probe and a tachometer conjointly on a large size
induction motor.
BACKGROUND OF THE INVENTION
Basic requirement of all A.C. Induction motors is to use a protection device as
speed switch, for locked rotor protection, in case when motor starting time is
more than the locked rotor time or difference between locked rotor time and
staring time is very less in different conditions. This speed switch arrangement is
normally provided external, at the non-drive end of motor.
Sometimes, A.C. Induction motors are also required to be provided with means
for mounting tachometer at non-drive end only.
Actual problem comes when both the speed switch arrangement and tachometer
arrangement are to be provided on the same motor.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved device for
mounting a speed switch acting as an auxiliary protection means, and a
tachometer functioning as a motor accessory, on a large rating induction motor.
Another object of the invention is to propose an improved device for mounting a
speed switch acting as an auxiliary protection means, and a tachometer
functioning as a motor accessory on a large rating induction motor, in which both
the speed switch and tachometer is simultaneously mounted on motor non-drive
end side, without any obstruction to each other.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved device for mounting a speed switch
and a tachometer on A.C. motors. According to the invention, an adaptor which
is square in shape with circular flange, which allows easy mounting over the
motor and remain concentric with the horizontal axis of the motors is disclosed.
The adaptor enables mounting of an inductive speed switch probe inside the
adaptor, which senses speed of rotation of a flag. The flag in turn is mounted on
a stub shaft. The tachometer is mounted on the same adaptor where the
inductive speed switch probe is mounted. However, the tachometer is mounted
on the adaptor with the help of a spigot and coupled with the stub shaft using a
flexible coupling. This stub shaft is the same one, on which metallic flag is
already mounted. The inventive process for mounting both the speed switch and
tachometer eliminates even a minor misalignment and can achieve a high level
of concentricity between the mating parts. In this way a simple and safe method
of mounting both speed switch and tachometer can be attained with high level of
accuracy and very minimum margin of error.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG-1 Section layout of an A.C. Induction Motor, showing mounting of speed
switch arrangement only, as per prior art.
FIG-2 Shows schematic of a Stub Shaft and a Flag, as per prior art.
FIG-3 Section layout of an A.C. Induction Motor, showing mounting of
tachometer as per prior art.
FIG-4 Shows section layout of an A.C. Induction Motor, including the inventive
device for mounting of the speed switch and a tachometer according to the
invention.
FIG-5 Schematic of a Stub Shaft of the device of Figure 4.
FIG-6 Schematic of a square adaptor with flange of the device of Figure 4.
DETAIL DESCRIPTION OF THE INVENTION
FIGURE - 1 Shows a typical Cross Sectional Layout of large rating A.C.
Induction motor in TETV (Totally Enclosed Tube Ventilated) construction. In this
arrangement, a stub shaft (3A) is fitted over a main shaft (5A) and a flag (2A) is
mounted over the stub shaft (3A) as shown in figure 1 & 2. The flag (2A) along
with the stub shaft (3A) rotates with same speed as that of the main shaft (5A)
of A.C. Induction motor. An inductive speed switch probe (1A) is fitted inside a
round adaptor with flange (4A), as per prior art. When the flag passes across the
face of the probe, the frontally radiated electromagnetic field of the probe is
converted to a corresponding output pulse which is digital in nature. In this way,
speed of rotation of the shaft can be judged.
FIGURE-3 Shows a cross-sectional layout of an A.C. Induction motor in TETV
construction in this prior art arrangement of a tachometer (6A) is fitted over the
adaptor with flange (4B). The tachometer (6A) if further coupled with a stub
shaft (3B) with the help of flexible coupling (7A). The purpose of mounting
tachometer is to monitor the exact speed of motor in revolutions per minute
(RPM).
FIGURE-4 Shows a typical cross-sectional layout of an A.C. Induction motor and
also showing a device for simultaneously mounting according to the present
invention. In this inventive device, an inductive speed switch (IB) and a
tachometer (6B) are conjointly fixed over a common square adaptor with flange
(9). The tachometer (6B) is further coupled with a stub shaft (8) with the help of
a flexible coupling (7B). The Stub shaft (8) remains concentric with the main
shaft (5B), since it is fixed in a tapped hole which is made concentric with the
axis of the main shaft (5B). A flag (2B) is fixed over the stub shaft (8), which
when passes across the face of the inductive speed switch probe (IB), dampen
its electromagnetic field, which is converted to digital output pulse and the speed
of rotation of the main shaft is precisely determined.
WE CLAIM:
1. An improved device for mounting a speed switch probe and a tachometer
conjointly on a large size induction motor, the improvement comprising:
- a square adapter with a flange enabled to conjointly accommodate along
the periphery an inductive speed switch and a tachometer;
- a stub shaft coupled to the tachometer via a flexible coupling, the stub
shaft disposed in a tap hole configured concentric with the axis of the
main shaft of the motor; and
- a flag fixed over the stub shaft, the assembly of the stub shaft and flag
during rotation corresponding to that of the main shaft passing across the
inductive speed switch, wherein the electromagnetic field generated is
dampened by the device and converted to digital output pulse such that
the rotational speed of the main motor shaft can be precisely determined.
2. An improved device for mounting a speed switch probe and a tachometer
conjointly on a large size induction motor substantially as herein described
and illustrated with reference to the accompanying drawings.