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					         Grand Valley State University
        The Padnos School of Engineering




MEASUREMENT OF SENSOR PROPERTIES
  EGR 345 Dynamic Systems Modeling and Control




                    Jed Pipe

                September 17, 2002

                  Lab Partners
                   Nick Zackay
                   Hung Nguyen




                   Fall 2002
                           Table of Contents

Table of Contents _______________________________________________ 2

1. Purpose _____________________________________________________ 3

2. Operation of Sensors __________________________________________ 3

3. Apparatus ___________________________________________________ 4

4. Procedure ___________________________________________________ 4

5. Results _____________________________________________________ 7

7. Conclusions _________________________________________________ 9
                                          1. Purpose
    In this lab, the operation of four industrial and laboratory sensors is examined.



                                2. Operation of Sensors
    There are several different types of sensors, each having there own unique use. In general,
sensors convert physical properties to measurable data, usually voltage or current. Sensors also
have a range of values of operation, maximum and minimum resolutions and sensitivities. There
are two main categories of sensors, discrete and continuous.
    Discrete sensors only have two states, open or closed. Examples of these types include:
      Inductive Proximity Sensors use magnetic fields to sense the presence of metals
      Capacitive Proximity Sensors use capacitance to sense most objects
      Optical Proximity Sensors use light to sense an object
      Contact Switches use physical contact to sense an object
   Continuous sensors output a range of values. Examples of these types include:
      Potentiometers provide a resistance proportional to an angle or displacement
      Ultrasonic Range Sensors provide a voltage output proportional to distance
      Stain Gauges change their resistance as they are stretched
      Accelerometers output a voltage that is proportional to their acceleration
      Thermocouples output small voltages proportional to temperature


    In this lab, a capacitive proximity sensor, an inductive proximity switch, a potentiometer,
and an ultrasonic range sensor are examined. The capacitive proximity sensor is designed for
non-contact sensing of a wide variety of materials, while the inductive proximity switch is
designed for contact sensing of only metals. The ultrasonic range sensor can sense a solid or a
liquid up to one meter away. The sensor outputs a voltage that varies linearly with the distance
of the sensing object.




                                             3
                                         3. Apparatus
   Table 1 lists all the equipment used in order to set up the capacitive proximity sensor.

                         Table 1 – Equipment for Capacitive Proximity Sensor

                       Item            Manufacturer      GVSU #       Serial Number

                  CADET Trainer              --             --           233192

                 Digital Multimeter        Fluke          18680                --

                Capacitive Proximity   Allen Bradley        --            875CP
                      Switch
                   Assorted Wires            --             --                 --




                                         4. Procedure
Capacitive Proximity Switch

   1. Referring to Figure 1 below, connect the leads of the wire to the CADET Trainer and the

      multimeter. (the load refers to the multimeter)

   2. Attach the quick connector from the wire to the switch.

   3. After the sensor is wired correctly, place the sensor on the table next to a ruler.

   4. With a piece of paper or a material that is not plastic, measure the operating distance of

      the sensor. (The approximate distance of operation should be between one and two

      centimeters)




                 Figure 1: Wiring diagram for capacitive proximity switch

                                             4
Inductive Proximity Switch

   1. Connect the brown wire to the +V on the CADET trainer.

   2. Connect the blue wire to the ground on the CADET trainer.

   3. Connect the black wire to the digital multimeter (DMM).

   4. Connect the ground of the DMM to the ground of the CADET trainer.

   5. Check the operation of the switch by touching a metallic object to the end of the switch

      Note: There is no fourth wire as shown in the wiring diagram below.




                 Figure 3: Wiring diagram for inductive proximity switch.



Ultrasonic Range Sensor

   1. Connect the blue wire to -V on the DC power supply

   2. Connect the brown wire to +V on the DC power supply

   3. Turn on the DC power supply and set to 18-30 volts

   4. Connect the black wire (load) to the multimeter and the ground of the multimeter to the

      ground of the DC power supply. Turn the DMM on.

   5. Set the wood block at a distance of 30 to 100 cm every 10 cm and record data.




                                           5
                      Figure 3: Wiring diagram for ultrasonic range sensor.



Potentiometer

   1.   Verify that the fixed   5V output from the power supply is 5V using the DMM, and the

        variable voltage source is 10V.

   2.   Connect the leads labeled CCW and CW to the power supplies, with a common ground.

        Connect the lead labeled Slide to the DMM.

   3.   To verify that the potentiometer is functioning properly use the equation

                           
        vout  v2  v1  w   v1 and verify three different changes in the voltage from the
                          l 
                          max 

        potentiometer. The voltages measured should be approximately close to the calculated

        values. (Hint: make a mark on the shaft and turn 90 degrees for each measurement)




                                              6
                    Figure 4: The wiring schematic for the potentiometer



                                          5. Results
    Capacitive Proximity Sensor
       The capacitive proximity sensor operated as planned. When there was no object near the
sensor, the voltage reading on the digital multimeter was around zero, but when an object was
placed within a centimeter of the sensor, the voltage increased to the input voltage which was
around fifteen volts. Besides the voltage, the operation of the sensor could also be known
because there was an LED on the sensor that lit up when the sensor detected an object. It was
also observed that the sensor detected most objects, but the sensor did not detect some plastic
objects.


    Inductive Proximity Sensor
    The inductive proximity sensor only detects metallic objects, and the objects must come in
contact with the sensor. It could be seen that the metallic object had been detected because of the
voltage gain on the multimeter from zero to the input voltage, and because of the LED that lit up
when the sensor detected the object. Other nonmetallic objects were tested, and as thought, the
sensor did not pick them up.


    Ultrasonic Range Sensor

                                             7
                                                 .966                  30 
                                                 2.123                 40 
                                                                       
                                                 3.257                 50 
                                                 4.421                 60 
                                     voltage            dist ance  
                                                        V of the object by cm displaying a voltage
    The ultrasonic range sensor would detect the range
                                                 5.552                 70 
                                                 6.707                  80 
value proportional to the distance. The relationshipbetween voltage and distance was calculated
                                                 7.866                 90 
                                                
by measuring the voltages at different distances.                       
                                                 9.163                 100 
                                                          10
                                                 9.163




                                  Voltage (V)
                                                voltage    5




                                                 0.966     0
                                                               0          0.5        1
                                                               0.3      distance     1
                                                                     Distance (cm)


          Figure 5: The Measured voltage and distance of the ultrasonic range sensor.
    The relationship between voltage and distance can be estimated from these data points by
using linear regression.
                             Dis tan ce  8.607  Voltage  21.908                                 (1)


    Potentiometer
       The potentiometer would measure a change in rotation angle. This change in angle
causes the output voltage of the potentiometer to change. The relationship between the voltage
and the rotation angle is also a linear relationship and can be determined using linear regression.
             Table 2: Measured voltage and angle displacement of the potentiometer.
           Rotation Angle (radians)                                                  Voltage (V)
                        0                                                                10
                       2π                                                                9.93
                       4π                                                                9.84
                       6π                                                                9.75


                                    74.546  Voltage  745.942                                  (2)




                                                                8
                                      7. Conclusions
    This lab was a success because the objective was completed. The operation of four different
sensors was examined. The best uses for the capacitive proximity sensor would be when a
variety of materials need to be detected. The best uses for inductive proximity sensors would be
when only metallic objects need to be detected. The best uses for ultrasonic range sensor would
be when the distance of an object must be known. The best uses for the potentiometer would be
when the angle of rotation must be known.




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