Capabilities
The capabilities of a PLC are best explained by considering typical
specifications. The PLC considered here is the Siemens CPU100 model, which has
the following specification features:
CPU 100
Digital I/O maximum ..........100
Analogue I/O maximum .........8
Digital input modules:
- 24 V DC
- 24 to 60 V DC
- 115 V AC
- 230 V AC
Digital output modules:
- 24 V DC/0.1 to 2 A
- 115 to 230 V AC/1 A
- Relay (5A @ AC 250 volts)
(resistive) (2.5 A @ DC 30V)
Internal Features:
Execution times (approx.)
- per binary operation 70uS
- per word operation 125uS
Memory internal RAM
- 1024 statements
Memory submodule
- EPROM/EEPROM
Flags (internal relays)
- 1024; 512 retentive
Timers:Number/range
- 16; 0.01 - 9990s
Counters:Number/range
- 16; 8 retentive
- 0-999 (up/down)
4 function math's
Data handling (BCD)
The PLC can be further enhanced by the use of the following units:
- Communications interfaces
- External timers
- Real time clock
- Temperature sensor amplifier
- Position control module
- Stepper motor contol module
In addition to this, there are a number of different programming panels,
dedicated programmers, and a choice of PC programming software (SIMATIC S5 STEP
(R) 5 LADDER 90 or SIMATIC S5 STEP (r) 5 as used on PG7xx series programmers)
available for use with the Siemens S5 PLC range. From the above, it is clear
to see that a PLC is capable of fulfilling most industrial control
applications. As the complexity of control applications increases, PLC
manufacturers are adding to their product ranges to keep pace. Essentially,
there is enough off-the-shelf hardware available to meet the most stringent
process control requirements.
|