Introduction to Industrial Automation

Figure 3.28  Automation circuit of the electrically driven gate of Figure 3.27.

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Industrial Automation Synthesis 

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103

Table 3.1  Symbols of Switching Contacts and Automation Devices

a) NC contact of a relay

b) NO contact of a relay

Any kind of electromagnetic 

contactor, relay and 

electrically operated switch

a) Button with NC contact

b) Button with NO contact

On-delay timer

Contact of a sensor e.g., limit 

switch

a) NC contact 

b) NO contact

Off-delay timer

Hand-operated switch

a) SPDT

b) SPST

Pulse type relay

Contacts of an On-delay timer

a) NO contact

b) NC contact

Υ/Δ

Abbreviation symbol for a 

Star-Delta automation 

circuit

Contacts of an Off-delay timer

a) NO contact

b) NC contact

Lamp indicator

Contacts of an overload thermal 

relay

a) NO contact

b) NC contact

Siren alarm or horn

Terminals for connecting a 

remote device (Klemens)

Solenoid valve coil

a) Low-voltage melt-type fuse

b) Three melt-type fuses of a 

3-phase network

Measuring instrument

Single-line symbol

a) 3-pole power relay

b) 3-pole power switch

Main terminals of a thermal 

overload relay

Multi-line symbol of a 3-pole 

power relay

3-phase motor

(

Continued

)

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  Introduction to Industrial Automation

Table 3.2. In Chapters 3 and 4, and based on these two tables, the industrial automation design 

will take place.

Another issue that arises with the design of large industrial automations is that of the relay’s 

contact location definition, especially when distributed in a size automation circuit. As an exam-

ple, the automation circuit in Figure 3.29 is considered, which represents the starting automation 

based on a Y/

Δ

 configuration, which is still different from the one examined in Section 3.4.2. 

Based on this automation circuit example, and in order to define the exact number and location of 

the required relay contacts, the following procedure should be followed:

  1. We number all the vertical branches of the automation circuit.

  2. Under each relay, we create a small table with two columns, with the notations “O” and “C” 

representing the number of open and closed contacts, respectively.