Experim ent 3
Title: Study of inductive, capacitive and optical proximity sensors and switches.
Objectives:
• To record the specifications, measurement characteristics and analyze the
applicat ion aspects of inductive proximity switches.
• To record the specifications, measurement characteristics and analyze the
applica tion aspects of capacitive proximity switches.
• To record the specific ations, measure ment characteristics and analyze the
applicat ion aspects of optical proximity switches.
Procedure:
• Record the following specifications for the inductive & proximity switch
provided.
1) 2 wire, 3 wire or 4 wire type (how do these types differ?)
2)
3)
DC type or AC type (i.e., the nature of the supply voltage required for its
operation).
The supply voltage range. (what factor determines the actual supply
voltage used for operating the proximity switch?)
4) The geomet ry of the proximity switch enclosure and the diameter of the
target face. While the body of the switch is metallic, the sensing face of the
switch has a plastic cap. Why is this so? (Why are Inductive proximity
switches available in different housing diameters?)
5) Details of the output stage - PNP type or NPN type, and the current rating.
6) The nature of the output, NO or NC type.
• Connec t the proximity switch to an appropriate power supply. Connec t a DMM
(in DC volts mode) to the output of the proximity switch. Ensure there is no
metallic target in the front of the switch. Note the output voltage recorded by
the DMM and note the status of the LED provided on the back of the proximity
switch housing. Is the output activated in the absence of the target? Is the output
of NO or NC type? Justify.
•
Place the mild steel target provided in front of the sensor and move it gradually
towards the face of the sensor. Record the distance at which the output is
activated . What is the sensing range of this proximity switch? Once the switch
output is activated, gradually retract the target (move it away from the sensor
face). Does the output of the switch activate and deactivate for different
positions of the target? Does this switch exhibit a Hysteresis?
• Repeat the above step using an aluminum target instead of a mild steel target. Is
the sensing range the same as recorded in the previous step? Does the sensing
range depend on the target material? Why is this so?
Use a plastic/ cardboard target. Is it sensed by the inductive proximity switch?
• Repeat the above steps using a capacitive proximity switch. How does if differ
from the inductive proximity switch?
•
•
Record the specifications of the photoelectric switches provided (the through
scan type, retro-reflective type and the diffuse reflectance type).
1)
2 wire, 3 wire or 4 wire type.
2)
DC type or AC type.
3)
The supply voltage range.
Details of the output stage - PNP type or NPN type.
4)
5) The nature of the output, NO or NC type.
•
Connect the optical proximity switches to an appropriate power supply. Connect
a DMM (in DC volts mode) to the output of the proximity switch. Ensure there
is no opaque target in the front of the switch. Note the output voltage recorded
by the DMM and note the status of the LED provided on the back of the
proximity switch housing. Is the ou~Jut activated in the absence of the target? Is
the output of NO or NC type? Justify. How is the sensing range of these switches
defined?
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