In the practice of electrical control and PLC input connections, it is common to use this resource, as it is practical and fast without generating high costs. First, it is necessary to understand the meaning of the acronym PnP/NpN, many already associate it with the PNP and NPN transistor, we will approach it in another way with practical examples. Using a digital sensor and a 24v DC lamp.
PnP
Using a 24v DC digital sensor, actuating it. It means that at its output terminal I have 24v DC (positive from my source). Using a 24v DC lamp, connecting one terminal to the negative/reference of the source.
NpN
Using a 24v DC digital sensor, actuating it. It means that at its output terminal I have 0v DC (negative/reference of my source). Using a 24V DC lamp, connecting one terminal to the positive of the source (24V DC).
Using the Relay Terminal
It is nothing more than a simple relay with a board. Using the board allows for LED monitoring of the drive, relay replacement, 24v DC power supply and quick assembly. The relay terminal is usually identified as A1 (+), A2 (-) being power supply. Outputs as 11 (common), 12 (normally closed) and 14 (normally open). Applying the PNP/NPN concepts, using the power supply terminals and the common of the relay terminal, the signal inversion is obtained as shown in the video below:
Advantages
Using a simple electrical control assembly allows the signal source to be inverted, avoiding the need to replace sensors or actuators. In addition, the cost of the relay terminal is low.
Disadvantage
The operating principle of the relay is by supplying power to the coil (AC/DC) and generating an electromagnetic field that attracts the metal armor, thus closing the contacts.
Mechanical wear occurs in the contacts and switching is not instantaneous, making it impossible to use in applications that require instantaneous switching.
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