automatismos prácticas de programación s7300 en lenguaje de

AUTOMATISMOS
5º Ingeniero de Telecomunicación
Curso 2003/2004
PRÁCTICAS DE PROGRAMACIÓN S7300 EN
LENGUAJE DE CONTACTOS KOP
1. Control de motores
2. Control de Válvulas
3. Guía de selección de temporizadores
MOTOR CONTROL EXAMPLE
Introduction
This article is designed to provide a practical example of software coding of motors for use in
Programmable Logic Controllers (PLC).
This example can be used for most applications for the control of motors via a PLC including pumps,
conveyors, mixers, etc. This article discusses the states a motor can be detected, it control and PLC
Software Programming.
This example is designed in in the most common PLC Programming Language - Ladder Logic.
Digital Inputs
For this example we have considered the following Digital Inputs to the PLC. Inputs may be excluded
where the signal is not available or not required by your application
Symbol
Description
AUTO
Automatic Selection
MAN
Manual Selection
ON State
OFF State
AUTO
------
MANUAL
------
START_PB
Manual Start Push-Button
START
------
STOP_PB
Manual Stop Push-Button
------
STOP
RESET
Alarm Reset Push-Button
RUN
Motor Running, contactor feedback.
RUNNING
STOPPED
ESTOP
Emergency Stop, aux contact from
emergency stop circuit.
STOP
HEALTHY
TRIP
Motor Tripped Signal, aux contact from
motor overload.
TRIPPED
HEALTHY
Notes:
•
•
For this article we have assumed that the auxiliary contacts for the emergency stop and the
motor overload will be ON for the trip condition.
The automatic controls have not been shown in this article as these signals will be derived from
the sequencing software.
Digital Outputs
For this example we have considered the following Digital Inputs to the PLC. Inputs may be excluded
where the signal is not available or not required by your application
Symbol
Description
MOTOR_RUN
Motor Run Signal
ON State
OFF State
RUN
STOP
Note: For this article we have used a single output for the control of the motor.
Motor States
From the inputs available the following states of the motor can be derived. We have shown the automatic
states in the following table, each state exists for manual mode and the auto text replaced by manual.
Symbol
Description
Motor Stopped (Symbol either black on a white background else white)
Motor Running
Motor Alarm (Emergency Stop/Failed - symbol can be flashed to draw the operators
attention)
Motor Tripped
Control Logic
Detecting, Latching and Reporting Alarms
The first alarms that will be detected within the logic are Emergency Stop and Tripped. This is simple
digital logic. These signals must be hardwired into the motor control circuit, but the software will
duplicate the hardwired logic to report the alarm to the operator.
Detect and Latch Emergency Stop
| ESTOP
ESTOP_AL |
|---| |-------------+--------------------------------(
)---|
|
|
| ESTOP_AL RESET
|
|---| |------|/|----+
Detect and Latch Motor Overload Trip
|
TRIP
TRIP_AL |
|---| |-------------+--------------------------------(
)---|
|
|
| TRIP_AL RESET
|
|---| |------|/|----+
The first two rungs of the above ladder diagram are used to detect and latch the Emergency Stop
conditions. When the alarm is detected then the condition is latched until
1.
The alarm condition is cleared
2.
The operator resets the alarm.
The next alarm condition is detecting that the motor has failed. That is that the PLC has requested for the
drive to start but the contactor has not closed. This could be due to a number of reasons, motor isolated,
fuse blown etc.
Detect Motor Failed To Start/Stop
| MOTOR_
_________________
| RUN
RUN
|ON DELAY
| |
|---| |------|/|----+--------------------|TIMER
M1_DELAY|-|
| MOTOR_
|
|TIME
1.0S |
| RUN
RUN
|
|_________________|
|---|/|------| |----+
Latch Motor Failed To Start/Stop
| M1_DELAY
MOTOR_AL |
|---| |-------------+--------------------------------(
)---|
|
|
| MOTOR_AL RESET
|
|---| |------|/|----+
In the first rung we use a timer to time the conditions when the motor is contactor does not match the
required PLC output. That is PLC run output is and the contactor is not closed and visa versa. In the
second rung we latch the alarm condition.
Combining The Alarms
| ESTOP_AL
M_ALARM |
|---| |--------+-------------------------------------(
)---|
|
|
| TRIP_AL
|
|---| |--------+
|
|
| MOTOR_AL
|
|---| |--------+
Here we use simple "OR" logic to combine the alarms, when any one of the alarms are detected the
M_ALARM is "ON".
Automatic and Manual Status
We use the selection of the automatic and manual for the control of the drive. It is written to ensure that
their is a scan difference during change over from automatic to manual so that the drive is stopped. This
is used in the Low Level Plant Driver.
Automatic Selected
|
AUTO
MAN_SEL
AUTO_SEL |
|---| |------|/|----+--------------------------------(
)---|
|
Manual Selected
|
MAN
AUTO_SEL
MAN_SEL |
|---| |------|/|----+--------------------------------(
)---|
|
Low Level Plant Driver
The low level plant driver is the final software which drives the output to the motor having considered all
the input output signals.
Control Motor
| AUTO_SEL AUTO_RUN
M_ALARM
MOTOR_RUN |
|---| |------| |----------------+----|/|--------------(
)---|
|
|
| MAN_SEL
START_PB
STOP_PB |
|---| |---+---| |-----+---|/|---+
|
|
|
|
| MOTOR_RUN |
|
+---| |-----+
When Automatic is selected then sequence flag (AUTO_RUN) is used to control the drive.
When manual is selected the drive will start when the start push-button is pressed, latched with the output
from the PLC (MOTOR_RUN). The drive will continue to run until the stop push-button is pressed.
Should any of the alarms be detected then the motor is stopped. The alarm must be reset before the motor
can be restarted.
EJEMPLO DE CONTROL DE VALVULAS
Realice en lenguaje KOP y empleando la guía adjunta de selección de temporizadores de Step 7,
el control del sistema de válvulas descrito a continuación.
ENTRADAS DIGITALES
Estado
ACTIVO
Símbolo
Descripción
OPEN_REQ
Selector de solicitud de apertura de válvula
ABRIR
LSO
Final de carrera abierto
ABIERTA
LSC
Final de carrera cerrado
CERRADO
RESET
Pulsador de cancelación de alarma
RESET
ESTOP
Pulsador (botón) de emergencia
PARAR
SALIDAS DIGITALES
Estado
ACTIVO
Estado
INACTIVO
Indicación al panel de
operación de maniobra de
apertura en curso
ABRIENDO
----------
V_CLOSING
Indicación al panel de
operación de maniobra de cierre
en curso
CERRANDO
----------
OV
Apertura de válvula
ABRIR
CERRAR
Símbolo
Descripción
V_OPENING
ESTADOS DE LA VÁLVULA
La válvula puede estar en cinco estados diferentes:
a)
b)
c)
d)
e)
cerrada (CERRAR_RET)
abriéndose
abierta (ABRIR_RET)
cerrándose
Situación de alarma (ALARMA)
LÓGICA DE CONTROL
La alarma se puede disparar por las siguientes razones:
1. Pulsador de emergencia
2. Fallo al abrir válvula
3. Fallo al cerrar válvula.
Para cada posición de las válvulas el sistema detecta condiciones de alarma. Estas son:
1. Fallo en apertura
-
La salida de apertura de válvula está activa (OV=1) y tras 10 segundos no
se activó LSO
ó
-
Estando la válvula en estado abierto (marca ABRIR_RET automantenida
que se activa cuando la válvula termina de abrirse y se desactiva cuando
OV=0), se desactiva LSO durante más de 1 segundo.
2. Fallo en cierre
-
La salida de apertura de válvula está inactiva (OV=0) y tras 10 segundos no
se activó LSC
ó
-
Estando la válvula en estado cerrado (marca CERRAR_RET similar a
ABRIR_RET para la maniobra de cierre), se desactiva LSC durante más de
1 segundo.
La situación de alarma se mantendrá hasta que se cumplan las dos siguientes condiciones:
1. La condición de disparo de la alarma ya no está presente.
y
2. Pulsación del botón de cancelación de alarmas.
CONTROL A BAJO NIVEL DE LA VALVULA
La señal OV estará activa cuando el selector del panel de operación OPEN_REQ esté activo y
no haya activa ninguna alarma.
PANEL DE INDICACIÓN/OPERACION
Indicación mediante V_OPENING y V_CLOSING de la maniobra que se está realizando antes
de que ésta concluya (suponga que no existen averías).
GUIA DE SELECCION DE TEMPORIZADORES
CONEXION EJEMPLO DE UN TEMPORIZADOR GENERICO EN KOP