Introduction to Industrial Automation

voltage release coil (b).

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Hardware Components for Automation and Process Control 

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counter value will express the total number of passed bottles in front of a photocell application. 

Electromechanical counters accept pulse input signals from sensors, switches, and relay contacts. 

When the output contact of a sensor closes, the automation circuit supplies the nominal voltage to 

the counter input, causing one increment per voltage pulse. The counters usually have a 3–6 digit 

display, which may have presetting capabilities and accept manual or electric reset.

Hour meters are used in applications where time duration is critical. To make a process more 

effective and safe, hour meters are used to determine how long a machine has been running in 

order to schedule machine maintenance or to start another process at a predetermined point in 

time. Electromechanical hour meters are designed for the determination and monitoring of the 

operating time of electrically driven machines, and are therefore connected in parallel to corre-

sponding relay coils. Obviously, an hour meter will only work during the operation of a machine 

or device. In Figure 2.65b, a panel-mount hour meter for industrial use is shown. In general, there 

are a wide range of electromechanical hour meters in all common voltages (AC or DC) and in 

various mounting styles.