SICK WTT12-S Instrucciones De Funcionamiento página 15

3.6 Test input
3.7 Sensor output behavior
8029123/2024/01/15 | SICK
Subject to change without notice
To ensure a correct implementation of the safety function, the detection corridors in
section 4.6.1 must be taken into consideration.
The sensor provides a test input that can be used to invert the sign of the offset for
setting the threshold and can thereby switch between an "operating mode" and a "test
mode". The switching is performed by the downstream logic unit or controller.
In "Test mode", the request for the safety-related function should be simulated in order
to monitor the correct sensor function.
The polarity of the test input for the two safety-related functions must be such that it
is opposite to the expected output in order to avoid "TEST PASS" feedback due to a
short-circuit between the output and the test input.
Table 3: Test input
Function
Object between sensor and
reference
Absence of reference
The cyclic test as the basis for the required diagnostic coverage must be performed
with at least 100 times the average expected demand rate for the safety function (cf.
test rate in table 11). Failure to pass the test must result in the application being put in
a safe state.
Defined states at the output
•
ACTIVE: Output signal modulated by a frequency with a 50/50 duty cycle between
HIGH/LOW (equal pulse/pause ratio). This output behavior indicates that the appli‐
cation is running as expected.
• INACTIVE: Sensor outputs a LOW signal. This output behavior represents the
safety-related state, i.e., the safety function is requested or an internal sensor
error is present. A downstream controller or logic must put the application in a
safe state as a result.
The output switches to ACTIVE if the measured distance is less than the set threshold
(depending on the sensor type). Otherwise the output is INACTIVE. If the distance
cannot be evaluated (e.g., due to an internal error), the output is INACTIVE.
Other output signals that occur (e.g., permanent HIGH signal) represent faulty sensor
states and must result in the initiation of a safe state in the application.
Object between sensor and reference
Object between sensor and reference function:
OPERATING INSTRUCTIONS
Mode
Operating mode
Test mode
Operating mode
Test mode
O P E R A T I N G I N S T R U C T I O N S | WTT12-S
Test input
HIGH
LOW
LOW
HIGH
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