Siemens S5-135U/155U Digital Input, Digital Output, Signal Output, Short-Circuit, Detection

Digital Input/Output Modules

Digital Input	A digital input module converts the process signals to the internal signal
Modules	level in the module. Interference is suppressed by the input circuitry, and the
	logic states at the inputs are indicated with LEDs on the front strip of the
	module. With most digital input modules (except the 420), the signals are
	isolated from the central ground point when received. Inputs relating to the
	same group are isolated from inputs of another group, but not from each
	other.
Digital Output	The control signals processed in the PLC are output via digital output
Modules	modules at a signal level suitable for the actuator, e.g. contactor, solenoid
	valve, etc. For the voltages and currents required in the process, modules
	with appropriate output circuitry are available.
	With most digital output modules (except the 441), the signals are isolated
	from the central ground point when relayed to the outputs. Outputs relating to
	the same group are isolated from outputs of another group, but not from each
	other.
BASP	If a digital output module receives a ªcommand output inhibitº (BASP, cf.
	Programming Guide and Chapter 4) from the CPU, the outputs are set to
	zero.
	When the supply voltage of the central controller or expansion unit has been
	switched on or when the CPU is at STOP, the outputs are set to zero.
Signal Output,	Signal output H+ on digital output modules for direct voltage emits a signal
Short-Circuit	when a short-circuit to ground (L-) or overcurrent has been detected at one or
Detection	more outputs currently at logic 1. Only short-circuits which are effective for
	more than 0.5 to 1 s are detected. Short-circuits are only detected at
	connected outputs. The signal outputs are decoupled by diodes. Up to 16
	outputs can be connected in parallel. Ensure that isolation is not defeated by
	the parallel connection of outputs.
	To ensure functioning of the signal output, you must connect terminal 1L+ to
	24 V on the 441, 451 and 454 modules. On the 453 and 457 modules, the
	floating signal output must be powered separately.

System Manual	8-3
C79000-G8576-C199-06