SSP North AB
30/08/2018
Manual V2f
20
3.1.2 Solid-state transistor outputs
Up to SIL 3, Ple, Cat 4 redundant output
Up to SIL 3, Pld, Cat 4 redundant output
Each output has two transistors in series and each one is controlled by each processor. Each output is
therefore a redundant output up to a certain degree, (see PFH-d values and a note below). Both
processors are also checking the signal transmitted from the output. This way both CPU:s check the
actual voltage level and coded signals sent out from the output. A single output which detects an
external short circuit can turn of itself but not the external short circuit. We recommend double static
outputs for SIL3, Ple, cat 4.
Any of the 14 I/O can be set in the Simplifier Manager to different output types in ON and OFF state.
The selectable output types for an I/O are:
1. VDC/+V (maximum 0.5V less than supply voltage)
2. 0 VDC
3. OSSD = output voltage level is 0,5 V less than supply voltage and this type of output also
detects a short circuit to other OSSD outputs in the same unit and to internal and external
fixed voltages. If there is an external short circuit the relevant outputs will be shut off, set to
OFF state or to fatal error depending on the type of short circuit and on how the application
program is done. See the Safety Manager manual for more information. The check of the
output is done during a very short time (less than 150 micro seconds) when the voltage level
shall go down to 0V. The OSSD outputs are commonly used in the industry in safety devices
and for stop signals to machines. Up to 14 OSSD output can be selected in a Safety Simplifier.
Drawing shows 5 OSSD outputs with short circuit detection. Up to 14 OSSD outputs can be selected
from a Safety Simplifier. A short circuit between any of these or to external voltage, is detected as an
external fault. A short circuit to one or more outputs will set the output to 0 volt. Other outputs it the
same function block will be set to OFF state. The fault will be indicated on the LED panel.
The test interval is very short (below 150 micro seconds). A conductor or a relay connected to an
OSSD output will normally not fall during this time. See technical data for test interval specification.
Содержание Safety Simplifier
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