Introduction to Industrial Automation

Figure 2.67  Pulse trains of a two-channel encoder and zero index for resulting coding data.

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  Introduction to Industrial Automation

  2.9.  What kind of level switch should you select in order to detect the level of barleycorn inside 

a silo?

 2.10. Explain the operation principle of a thermal overload relay and the role of its electric contacts. 

 2.11. What kind of sensor is shown in the figure? What does it detect and how does it operate?

 2.12. A pump is automatically filling a tank via an electronic level switch with immersed elec-

trodes. The tank is emptying from an unpredictable consumer. At a random time interval, 

you are informed that the level is at height L. Based on this information only, can you con-

clude if the pump is operating at this time instance?

ELS

L

Pump

E1

E2

 2.13. A production machine produces metallic objects slightly connected to each other in the 

form of a chain. What kind of sensor you would use to monitor the continuity of chain and 

where exactly you would position the sensor?

Produced

objects

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Hardware Components for Automation and Process Control 

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77

 2.14. Give the time function response of the SPDT output of an On-Delay type and Off-Delay type 

of timer, both adjusted at 30 s in relation to the supply voltage V

in

 shown in the figure.

V

in

t

60 s

 2.15. Give the time function of operation of relay C for the continuous operation of the cam 

switch the time constant of which is ½ rpm. The time diagram must contain two complete 

rotations of the cam.

90°

T

T

C

ON-delay timer

adjusted at 20 s

Cam switch

 2.16. Suppose that you have a power relay with a coil of nominal voltage 24 V DC and a proxim-

ity switch of nominal operation voltage 230 V AC with an output of SPDT type. Explain if 

it is possible to combine the two devices, relay and sensor, in order to achieve an automatic 

operation of a machine which is fitted via the relay.

 2.17. In the three applications in the figure, we want to detect if the corresponding objects A, B, and 

C have reached the imaginary line XY. What kind of sensors you would select in each case?

X

Y

B

X

Y

C

X

Y

A

 2.18. The same voltage V

in

 is applied to the coil of a common general purpose relay and a pulse 

bi-stable relay. Complete the state-behavior of their NO contacts in the diagram.

V

in

0

Open

Closed

Open

Closed

Common

relay

 Pulse bi-stable

relay

t

t

t

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  Introduction to Industrial Automation

 2.19. The figure shows a sensor or switch for industrial use. Identify the type of the sensor and its 

possible features, and give the connection circuit of a load.

R 

N 

Load 

 2.20. What kind of sensor would you select in order to detect the lack of label on the bottle?

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