Changeover Contact Diagnostics - Siemens SIMATIC ET 200S Manual

Digital Electronic Modules
Diagnostics with the changeover encoder type
With the diagnostic functions for the changeover encoder type, the digital
electronic module monitors the changeover between two input channels. If there is
no signal transition at the NC contact when the specified changeover time (see
technical specifications) has expired, the module outputs diagnostics information.
Purpose
You can use the diagnostics function to
analyze the encoder
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verify that the switch has changed between the NO contact and the NC contact.
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Principle
If the digital inputs of a channel group are configured as "changeover contacts", the
module for this channel group carries out a diagnostics for the changeover contact
type of sensor. The tolerated changeover time between the two channels is set to
the fixed value of 300 ms.
If the plausibility check returns a negative result,
The module identifies the value status of the normally open contact channel as
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"invalid".
The module creates a diagnostic entry for the normally open contact channel.
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A diagnostics interrupt is triggered.
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The digital input signal and the value status are updated only for the NO channel
(channel 0, 2). For the NC channel (channel 1, 3), the digital input signal is set to
the fixed value "zero," and the value status is "invalid" because this channel is used
only for the validation of the sensor.
Note the following points in the diagnosis for the changeover contact type of
sensor:
• If there is already an error on the normally open contact channel (a wire break,
for example), the module no longer performs diagnostics for changeover
contact errors. Changeover errors are still monitored on the other channel.
• You will find further details in the table below:
Table 11-16 Changeover Contact Diagnostics
Changeover contact
Changeover switch as
NAMUR
changeover switch with
load resistance
changeover switch without
R-circuit
11-40
Negative check means ...
•
Short-circuit or
•
Wire break
•
Sensor defective or short-circuit
No distinction between a defective sensor and
short-circuit is possible.
Important: no differentiation possible between
•
"0" signal and wire break
•
"1" signal and short-circuit
Also:
Changeover error or
external error (in DP t l (i DP
diagnostics)
ET 200S Distributed I/O System
EWA-4NEB 780602402-12