Introduction
You can wire the BMXSAI0410 safety analog input module to analog sensors to achieve SIL3 compliance in several different ways, depending on:
the required Category (Cat2 or Cat4) and Performance Level (PLd or PLe) standard
your application’s requirements for high availability
| CAUTION | |
|---|---|
RISK OF UNINTENDED OPERATION The maximum safety integrity level (SIL) is determined
by the quality of sensor and the length of the proof-test interval
to IEC 61508. If you are using sensors that do not meet the quality
of the intended SIL standard, always wire these sensors redundantly
to two channels. Failure to follow these instructions can result in injury or equipment damage. | |
The following SIL3 digital input application wiring examples are described, below:
Cat2/PLd:
a single sensor wired to one input.
Cat2/PLd with high availability:
two sensors wired to two input points on different input modules.
Cat4/PLe:
two sensors, each wired to a different input point on the same input module.
Cat4/PLe with high availability:
two pair of sensors (for a total of four sensors): the sensors of the first pair are each wired to a different input point on one module, and the sensors of the second pair are each wired to a different input point on a second module.
SIL3 Cat2/PLd
The following example presents a single sensor wired to one input point on a single input module. The CPU performs 1oo1D evaluation on the single monitored value:
| CAUTION | |
|---|---|
RISK OF UNINTENDED OPERATION To achieve SIL3 according to IEC61508 and Category 2/Performance
Level d according to ISO13849 using this wiring design, you must use
a suitable, qualified sensor. Failure to follow these instructions can result in injury or equipment damage. | |
SIL3 Cat2/PLd with High Availability
The following example presents two sensors that monitor the same process variable. Each sensor is connected to a single input point on different input modules. The CPU performs 1oo1D evaluation of the single monitored value:
S_AIHA function block in the SAFE task to manage the two
process variable values reported by the two sensors.| CAUTION | |
|---|---|
RISK OF UNINTENDED OPERATION To achieve SIL3 according to IEC61508 and Category 2/Performance
Level d according to ISO13849 using this wiring design, you must use
a suitable, qualified sensor. Failure to follow these instructions can result in injury or equipment damage. | |
SIL3 Cat4/PLe
The following example presents two sensors that monitor the same process variable. Each sensor is connected to a single input point on the same input module. The CPU performs a 1oo2D evaluation of the competing values provided by the two sensors for the same process variable:
S_AI_COMP function block in the SAFE task to perform a 1oo2D
evaluation of the competing values coming from the two sensors.| CAUTION | |
|---|---|
RISK OF UNINTENDED OPERATION To achieve SIL3 according to IEC 61508 and Category 4/Performance
Level e according to ISO13849 using this wiring design, you must use
a suitable, qualified sensor. Failure to follow these instructions can result in injury or equipment damage. | |
SIL3 Cat4/PLe with High Availability
The following example presents two pair of redundant sensors, which monitor the same process variable. Each sensor is connected to a single input point on two different input modules (two inputs on each module). This design makes it possible for the CPU to perform a 1oo2D evaluation:
S_AI_COMP and S_AIHA function blocks inside the SAFE task to manage the four input signals:S_AI_COMPto perform 1oo2 evaluation of two pairs of values coming from both sensors connected to the same module.S_AIHAto manage the high availability feature.
The following function block diagram depicts the above referenced code segment design:
| CAUTION | |
|---|---|
RISK OF UNINTENDED OPERATION To achieve SIL3 according to IEC 61508 and Category 4/Performance
Level e according to ISO13849 using this wiring design, you must use
a suitable, qualified sensor. Failure to follow these instructions can result in injury or equipment damage. | |