Introduction to Industrial Automation

Figure 1.4  Multi-state electric motors are controlled by two state power relays.

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Industrial Automation 

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switch (knob), etc. In the case that the operation of the integrated machine is set in the “manual” 

mode, the operator is utilizing the operation devices for turning on the desired motors or the 

actuators and in the proper sequence. In the case that the integrated machine is set in the “auto” 

mode, the operator is again utilizing the operation devices, either for initiating the operation 

mode, or for instructing the integrating machine to change the operational state. As an example, 

in an integrating machine for chocolate production, the operator is capable, by the press of a but-

ton, to order the control system to alter the current recipe production for another one. In this 

case, the control system should allow the integrated machine to complete the current operation 

and afterwards, ensuring the prerequisite quantities for executing the ordered recipe change, to 

command the integrated machine in executing it. In most cases, the automation system of an inte-

grated machine provides both the functionalities of an automatic or manual mode of operation, 

especially for dealing with the emergency fault situations, where direct manual control of all the 

provided automatic functionalities of the integrated machine is needed.

The operation control devices have also two states of operation, OFF and ON, similar to the 

cases of the motors and the actuators. As presented in Figure 1.5, a pressed button is energized 

and thus is in the ON state, while a non-pressed button is not energized and is in the OFF state. 

The ON state is independent of the time duration that the button is pressed and of the switching 

contact type (open or closed) in the not-energized state.

The next category of the machines presented in Figure 1.3 are very commonly installed in 

industrial environments, and are the indication devices that are utilized for transmitting process 

information from the integrated machine to the operator. In most cases, the industrial process is 

widely geographically distributed, and thus the operator that is in charge of the whole process has no 

direct visual or audio feedback from the process and the overall operation of the multiple integrated 

machines. However, even in the case that a visual or audio feedback is available, for safety reasons 

human senses are considered unreliable, and these monitoring, displaying, and visualizing devices are 

still needed to track the performance and state of operation of the industrial process. Especially in the 

cases of measuring variables without a direct visual or audio effect (like the variables of pressure, tem-

perature, flow of a liquid in a non-transparent tube, etc.), such monitoring devices are of paramount 

importance. In most cases, this information is transmitted to the operators through the utilization 

of light or audio indicators, which can be again considered as devices with an ON and OFF state.

In a large set of integrated machines, specialized sensors for performing specific measuring of 

quantities are utilized extensively. For example, such sensors can be utilized to sense if there is a 

flow of a liquid in an opaque tube, if the level of a tank has reached a certain height, if the moving 

part of a machine has reached the desired place, if the temperature of a reactor has been set to the 

nominal one, etc. In general, these sensors can be categorized in digital and analog sensors. The 

digital sensors are characterized by two states of operation, namely ON and OFF or 1 and 0, cor-

respondingly. The analog sensors are able to produce an analog (continuous) measurement of the 

quantity under study and thus more complicated hardware and software is needed to incorporate 

the industrial automation for utilizing this information.

Rest state

Rest state

OFF

ON

OFF

ON