How to Wire Discrete DC Sensors to PLC - Part 2
Summary
TLDREn este video, aprenderás cómo conectar un sensor de proximidad inductivo de tres cables a una tarjeta de entrada PLC, además de comprender qué es un sensor discreto de tres cables y algunos de sus tipos comunes. Se detalla cómo los sensores de CC discreta operan en dos estados (encendido y apagado) y cómo se utilizan en un circuito PLC para controlar motores de cinta transportadora. También se explican las diferencias entre sensores NPN (sinking) y PNP (sourcing), y la correcta forma de cablear estos sensores a tarjetas de entrada digitales PLC.
Takeaways
- ⚙️ Los sensores de corriente continua (DC) de tres cables, como los sensores de proximidad inductivos, pueden conectarse a una tarjeta de entrada de un PLC.
- 🔌 Un sensor discreto de tres cables tiene dos estados operativos: encendido y apagado, y se utiliza para controlar procesos a través del PLC.
- 💡 Los sensores de proximidad detectan objetos cercanos y permiten al PLC tomar decisiones como encender o apagar motores, como el de una cinta transportadora.
- 🔧 Los sensores discretos DC de tres cables requieren una fuente de alimentación de 24V DC para funcionar correctamente en los circuitos PLC.
- 📊 Existen dos tipos de sensores discretos de tres cables: NPN (sinking) y PNP (sourcing), que se conectan de manera diferente a las tarjetas de entrada del PLC.
- 📋 Los sensores NPN se refieren a 'sinking' y requieren una tarjeta de entrada sourcing, mientras que los sensores PNP son 'sourcing' y necesitan una tarjeta sinking.
- 🔗 Los sensores de proximidad de tres cables tienen una convención de cableado donde el cable marrón va al positivo, el azul al común, y el negro al terminal de entrada del PLC.
- ⚡️ Los sensores PNP y NPN no deben mezclarse en la misma tarjeta de entrada del PLC, ya que esto puede provocar fallos en el sistema.
- 🖥️ Las tarjetas de entrada digitales del PLC, como la Siemens SM 321, están diseñadas para trabajar con sensores PNP y requieren una fuente de 24V DC.
- 🔍 Es esencial consultar la hoja de datos del fabricante para asegurar una correcta configuración y conexión de los sensores a los PLC.
Q & A
¿Qué es un sensor discreto de tres hilos?
-Un sensor discreto de tres hilos es un dispositivo utilizado para detectar el estado de un objeto o proceso, tiene dos estados de operación: encendido y apagado.
¿Cómo se utiliza un sensor de proximidad inductivo de tres hilos en un sistema PLC?
-El sensor de proximidad inductivo se conecta a una tarjeta de entrada del PLC, donde detecta la presencia de un objeto y permite al programa del PLC tomar decisiones, como iniciar o detener un motor.
¿Qué función tiene el suministro de energía en los circuitos DC de un PLC?
-El suministro de energía en los circuitos DC proporciona energía a los dispositivos conectados, como interruptores de proximidad o motores, generalmente a 24V DC.
¿Qué diferencias existen entre los sensores NPN y PNP?
-Los sensores NPN, conocidos como 'sinking', conectan la carga a tierra cuando cambian de estado, mientras que los sensores PNP, conocidos como 'sourcing', suministran 24V DC a la carga cuando cambian de estado.
¿Qué pasa si se mezclan sensores NPN y PNP en la misma tarjeta de entrada del PLC?
-Mezclar sensores NPN y PNP en la misma tarjeta de entrada del PLC puede generar condiciones inseguras y causar cortocircuitos en el sistema.
¿Cómo se conectan los sensores de tres hilos a una tarjeta de entrada digital del PLC?
-Para conectar un sensor de tres hilos a una tarjeta de entrada digital del PLC, el cable marrón se conecta al positivo del suministro de energía, el cable azul al común del suministro y el cable negro al terminal de entrada del PLC.
¿Cuál es la configuración estándar de los cables de un sensor discreto de tres hilos?
-La configuración estándar es: el cable marrón se conecta al positivo del suministro de energía (24V DC), el cable azul al terminal común (negativo) y el cable negro al terminal de entrada del PLC.
¿Por qué es importante revisar la hoja de datos del fabricante antes de conectar un sensor al PLC?
-Es importante revisar la hoja de datos del fabricante para asegurarse de que se conoce la configuración del sensor y se conecte correctamente al PLC, evitando errores de conexión o fallos de funcionamiento.
¿Qué tipo de tarjeta de entrada se necesita para conectar un sensor PNP?
-Para conectar un sensor PNP, se necesita una tarjeta de entrada que sea compatible con dispositivos PNP, conocida como tarjeta de entrada de tipo sinking.
¿Qué sucede cuando un sensor de proximidad detecta un objeto en un sistema PLC?
-Cuando un sensor de proximidad detecta un objeto, cambia su estado y cierra el circuito, lo que permite al PLC detectar la presencia del objeto y ejecutar una acción, como encender un motor.
Outlines
🔧 Introducción a sensores de corriente continua (DC) y su conexión a una tarjeta de entrada PLC
En este párrafo, se presenta el tema principal del video: aprender a conectar un sensor de tres cables, como un sensor de proximidad inductivo, a una tarjeta de entrada de un PLC. Además, se explican qué son los sensores discretos de tres cables y se mencionan algunos tipos comunes. También se hace una solicitud para que los espectadores den 'like' y se suscriban al canal de YouTube para recibir contenido valioso y gratuito.
⚙️ Funcionamiento de los sensores DC discretos en un PLC
Este párrafo explica cómo los sensores de corriente continua (DC) indican el estado de un dispositivo o proceso a un PLC, permitiendo que el programa del PLC tome decisiones como encender un motor de cinta transportadora. También se ilustra un ejemplo donde un sensor de proximidad detecta la presencia de una caja en una cinta transportadora, iniciando así el motor para mover la caja a la siguiente estación.
🔌 Explicación de los sensores DC discretos y su conexión
En esta parte, se explica cómo funcionan los sensores discretos de corriente continua en un circuito alimentado por una fuente de poder. Se destaca que estos sensores tienen dos estados operativos: encendido y apagado. Además, se describe el funcionamiento de un interruptor discreto DC y otros ejemplos de sensores discretos, como los de proximidad, nivel y presión. Finalmente, se menciona la importancia de conectar adecuadamente estos sensores a la tarjeta de entrada digital del PLC.
🧩 Tipos de sensores NPN y PNP en dispositivos de tres cables
Aquí se introduce la diferenciación entre los sensores NPN (sinking) y PNP (sourcing), que son dos tipos de transistores bipolares que actúan como interruptores de estado sólido. Se menciona la importancia de revisar la hoja de especificaciones del fabricante antes de la conexión y se ofrece una guía sobre cómo conectar los tres cables de un sensor de proximidad a una tarjeta de entrada digital de un PLC, diferenciando entre los sensores NPN y PNP según su función de 'sinking' o 'sourcing'.
📈 Ejemplo de conexión de un sensor de proximidad a un PLC Siemens
Este párrafo explica cómo conectar un sensor de proximidad PNP a una tarjeta de entrada digital de un PLC Siemens SM 321. Se detalla el esquema de la tarjeta, la disposición de los terminales y cómo se debe conectar cada cable del sensor (marrón, azul y negro) a los terminales de la fuente de alimentación y la tarjeta de entrada digital. Además, se explica cómo la tarjeta y el sensor utilizan la misma fuente de alimentación de 24V DC.
📚 Resumen y consejos finales sobre sensores de tres cables
En este párrafo se resumen los puntos clave aprendidos en el video, destacando los tipos de sensores de tres cables (NPN y PNP) y sus diferencias operativas. Se enfatiza la importancia de conectar correctamente los cables del sensor (marrón, azul y negro) al canal de entrada digital del PLC y se recomienda consultar los esquemas específicos de las tarjetas de entrada digital para realizar una conexión adecuada. También se anima a los espectadores a visitar el sitio web de RealParse para más recursos de formación en programación de PLC.
Mindmap
Keywords
💡Sensor de proximidad inductivo
💡PLC (Controlador Lógico Programable)
💡Tarjeta de entrada digital
💡Sensor discreto de corriente continua (DC)
💡Alimentación de corriente continua (DC)
💡Sensor NPN
💡Sensor PNP
💡Módulo de entrada SM 321
💡Diagrama de escalera
💡Cable de tres hilos
Highlights
Learn how to wire a three-wired DC sensor like an inductive proximity sensor to a PLC input card.
Understand what a three-wire discrete sensor is and recognize common types of three-wire discrete sensors.
Three-wire discrete sensors operate in a circuit with a power source, commonly a 24V DC power supply.
Discrete DC sensors have two states: on and off, with on meaning the circuit is complete, and off indicating the circuit is broken.
To monitor the state of a proximity sensor in the PLC, three wires are connected to a digital input card.
Proximity sensors change state when a part moves nearby, sending this data to the PLC to start a process, such as a conveyor motor.
Identifying whether the sensor is NPN (sinking) or PNP (sourcing) is key when connecting it to a PLC input card.
NPN switches sync the load to common, while PNP switches source voltage to the PLC input.
NPN and PNP sensors should never be mixed on the same PLC input card to avoid unsafe conditions.
Siemens SM 321 digital input card is an example of a 16-channel 24V DC input card used with PNP sensors.
The Siemens SM 321 input card wiring requires careful connection of the three wires for PNP devices: brown to 24V, blue to common, and black to the input terminal.
The SM 321 card is powered by a 24V DC supply connected to terminals 1 and 20 for the card's internal functions and inputs.
Marshaling terminals are used to simplify field wiring to the PLC input card for better organization in the control panel.
Three-wire DC sensors (NPN or PNP) must be connected to the correct PLC input card type for proper operation.
Connecting a PNP proximity switch to a PLC input requires wiring the black wire to the input terminal and ensuring the proper connection to the power supply.
Transcripts
in this video you'll learn how to wire a
three wired DC sensor like an inductive
proximity sensor to a PLC input card
you'll also learn what a three wire
discrete sensor is and recognize some of
the common types of three wire discrete
sensors
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DC sensors can be used to indicate the
state of a device or process to the PLC
program knowing these input states can
allow the PLC program to make decisions
such as when to start or stop a conveyor
motor
in this diagram the programmable logic
controller or PLC is running a ladder
logic program
the inductive proximity switch is
connected to a PLC input card and the
logic program is written to sense the
state of the switch
for instance when a box is placed on a
conveyor at the loading position the
proximity switch senses the presence of
the box and commands the conveyor motor
to start to transport the box to the
next inspection station
so let's see how we can make this
important discreet sensor input
information available to a PLC program
in order to do this we need to
understand more about these discrete
sensors and how they are wired to the
PLC
discreet DC sensors or discreet direct
current sensors operate in a circuit
with a battery or other power source
commonly known as a power supply
power supply is placed in an electrical
circuit to provide power to the
connected devices like proximity
switches or a motor
DC power supplies are referred to by
their voltage and capacity indicated by
how many amperes they can supply the
more amperes a power supply can deliver
the larger and more expensive
they generally are
in DC PLC circuits the power supply
almost always supplies 24 volts DC to
the connected devices
in this diagram a DC circuit is shown
which turns on a motor when a proximity
switch senses the presence of a part or
an object in a specific location the
common trait of all discrete DC sensors
is that they have exactly two operating
States on and off
a discrete DC switch as in this diagram
is on when an object is in proximity to
the switch and its internal contact is
closed forming a complete circuit and
allowing the flow of electrons
when the object is moved away from the
proximity sensor its contacts are opened
again the circuit is broken and the flow
of electrons stops the state of the
switch is off
other common examples of discrete DC
sensors include many other types of
proximity sensors level switches
pressure switches and photoelectric
sensors
if we want to monitor the state of a
proximity sensor in the PLC we would
need to connect the three wires of the
proximity sensor to a digital input card
in the PLC
when the proximity sensor does not sense
a part nearby the PLC would see the
input state as off or a zero the circuit
to and from the PLC input is open or not
energized
when apart moves in front of the
proximity sensor the PLC input senses
the change in state and transmits this
data through a communication channel to
the processor memory or data table
proximity sensor senses apart nearby the
circuit to and from the PLC input is
closed or energized
we could then write a PLC program which
resides in the memory of the PLC to take
some action like starting a conveyor
motor when a part is near the proximity
sensor
wiring a discrete DC sensor to a PLC
input card is easy and straightforward
in this video we will consider only
devices that have three wires that need
to be connected to the PLC digital input
card an example an inductive proximity
switch is shown here in a separate video
we will consider some simpler to wire
devices
for most PLC's the input cards must
match the type of circuit that will be
employed to interface the device to the
PLC for example a discrete DC device
must be wired to a discrete DC input
card
a discrete AC device would require a
discrete AC input card
in this video we will consider only DC
devices
in order to connect a three-wire
discrete DC device to the PLC we will
need to identify whether the device is
an NPN or a PNP type
NPN and PNP are two types of bipolar
transistors which are simply solid-state
switches you should always check the
manufacturers datasheet for the device
you are going to connect to the PLC to
make sure you know its configuration
for now just remember the NPN switches
are referred to as sinking and PNP
switches are referred to as sourcing
note that each of these sensors has
three wires wire three the black wire is
always connected to the load which is
the terminal for an input on a PLC
digital input card
in this simplified diagram of an
inductive switch there are three wires
one brown wire one blue wire and one
black wire
the standard convention is that the
brown wire is connected to the positive
side of the power supply plus 24 volts
DC and the blue wire is connected to the
DC common terminal of the power supply
this is the negative terminal that is
present on the power supply the black
wire is the output or load wire of the
sensor it gets connected to the PLC
input terminal
earlier we said an NPN sensor was
referred to as a sinking switch this
means that the load which is the PLC
input is wired as shown in this diagram
notice that plus 24 volts DC is wired to
the PLC modules common terminal in other
words when the switch changes state it
syncs the load to common or ground
for many PLC manufacturers connection of
NPN sensors requires a specific model
number for the digital input card
because NPN sensors are sinking they
require a sourcing type PLC input card
a PNP sensor is referred to as a
sourcing switch this means that the load
which is the PLC input is wired as shown
in this diagram
notice that the blue common wire is
connected to the PLC modules common
terminal in other words when the switch
changes state its sources or supplies
plus 24 volts DC to the PLC input
for many PLC manufacturers connection of
PNP sensors requires a specific model
number for the digital input card
because PNP sensors are sourcing they
require a syncing type PLC input card
because NPN sensors sync voltage and PNP
sensors source voltage to the PLC input
NPN and PNP sensors should never be
mixed on a PLC input card doing so can
lead to an unsafe condition
in this diagram in NPN and a PNP sensor
are both connected to the same PLC input
card
note that the common terminal has a
brown wire from the NPN sensor with plus
24 volts DC connected to a blue wire
from the PNP sensor which would short
the power supplied to ground now let's
see how three wire discrete DC sensors
are connected to actual PLC io cards
this is a schematic of one model of
siemens sm 321 digital input cart part
number 6 e s7 3 - 1 - 7 b h o1 - o
it is a 16 channel 24 volt DC digital
input card that is very popular in
siemens pc s7 and s7 300 PLC systems
this digital input card wiring scheme is
similar to most digital input cards used
in the process industries
the sm-3 21-7 BHO one has 20 screw
terminals to which the digital inputs
are connected as we saw previously for
three wired discrete DC sensors each
digital input channel requires the
connection of three wires
the SM 321 card is constructed so as to
accept only PNP type sensors in a three
wire configuration
use of NPN sensors would require a
different model of Io card
the SM 321 card requires 24 volts DC
power to perform several functions first
the card itself requires power to light
the status LEDs perform diagnostics and
to communicate the cards input statuses
back to the plc
power to the card is supplied by 24 volt
DC power supply connected to terminals 1
and 20
internally inside the sm-3 421 card this
same 24 volt DC power is connected to
terminals 10 and 11
the power at Terminal 10 supplies power
for the top group of eight digital
inputs and the power at terminal 11
supplies power for the bottom group of
eight digital inputs
let's just focus on the top eight inputs
labeled as input zero through input
seven in practice the PLC input card
channel connections terminals 2 through
9 and 12 through 19 will be brought out
to a terminal block
these marshaling connections as they're
called allow the field wires to be more
easily terminated in the control panel
these terminals are represented by the
letters A through H in this diagram the
installer usually pre wires the
marshaling terminals terminal 2 on the
SM 321 7b ha1 card to terminal a
terminal 3 to terminal B and so on
now let's connect a PNP inductive
proximity switch from the previous
example to the sm-3 21 card the eight
marshaling terminals a through H are
wired to channels 0 through 7 and are
the load terminals in our discrete
circuits
24 volts DC will be obtained from
Terminal 10
terminal 20 is connected to the power
supply DC common
for a PNP device care must be taken to
connect the brown wire to the 24 volt DC
terminal and the black wire to the PLC
input channel terminal
if we connect the proximity switch to
PLC input channel 3 then the black wire
will land on terminal a finally the blue
wire will be connected to the power
supply DC common terminal 20
when the proximity switch senses an
object nearby the state of the switch
will change in the input channel to
which the proximity switch is wired will
indicate an on state
both the electronics in the switch and
the PLC card are powered by the same 24
volt DC power supply
to review we have learned that there are
many types of discreet three wired DC
sensors that can be wired to a PLC input
three wire devices are NPN or sinking
sensors and some are PNP or sourcing
sensors the difference is in how the
device operates when the switch actuates
npn switches sync DC common to the black
wire where the switch is activated
PNP switches source 24 volts DC to the
black wire when the switch is activated
remember in both cases the black wire is
connected to the PLC input channel
terminal
for most three wired devices there's
typically one brown wire one blue wire
and one black wire
a schematic of your specific DC digital
PLC input card is required to determine
how your specific device should be wired
for a three-wire PNP discrete input
device the brown wire will be connected
to 24 volts DC the blue wire will be
connected to DC common and the black
wire will be connected to the PLC
digital input channel terminal
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