Siemens Simatic S7 Series User Manual

41
Discrete Inputs/Outputs
Motor Starter Example While the lamp application previously discussed is useful to
explain basic PLC operation, a more practical, and only slightly
more complex, application is start-stop control of an AC motor.
Before examining the PLC application, first consider a hard-
wired approach.
The following line diagram illustrates how a normally open and
a normally closed pushbutton might be connected to control
a three-phase AC motor. In this example, a motor starter coil
(M) is wired in series with a normally open, momentary Start
pushbutton, a normally closed, momentary Stop pushbutton,
and normally closed overload relay (OL) contacts.
O
N
O
F
F
l
O
100
100
Amp
T
ype/T
ip
o
NEG
Frame-EG
Motor
M
Starter Coil
Ma
Start Pushbutton
Stop Pushbutton
Auxiliary Contact
(Holding Circuit)
OL
L1
L2
L3
Circuit Breaker
M
M
M
OL
OL
OL
Contactor Overload Relay
T1
T2
T3
Momentarily pressing the Start pushbutton completes the path
for current flow and energizes the motor starter (M). This closes
the associated M and Ma (auxiliary contact located in the motor
starter) contacts. When the Start button is released, current
continues to flow through the Stop button and the Ma contact,
and the M coil remains energized.
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Siemens Simatic S7 Series Specifications

General

CPU	Varies by model (e.g., S7-300, S7-400, S7-1200, S7-1500)
Communication Interfaces	PROFIBUS, PROFINET, Ethernet, MPI
Programming	TIA Portal, STEP 7
Programming Languages	LAD, FBD, STL, SCL, GRAPH
I/O Modules	Digital, Analog, Specialty modules available
Operating Temperature	0°C to 60°C (standard models)
Mounting	DIN rail mounting
Operating Voltage	24V DC or 120/230V AC (varies by model)
Protection Class	IP20 (standard models)
Memory	Varies depending on the S7 model. Includes work memory (RAM) for program execution, load memory (EEPROM or Flash) for program storage, and system memory for operating system functions. Memory sizes range from kilobytes to megabytes.