Siemens Simantic ET 200S - Table 3-4 Diagnosis for Changeover Contacts

Digital electronic modules
3.9 4DI NAMUR digital electronic module (6ES7131-4RD01-0AB0)
ET 200S
Manual, Edition 10/2005, A5E00514527-01
3-41
Diagnosis for changeover contact sensor types
When a diagnosis is made for the changeover contact sensor type, the digital electronic
module controls the switchover between two input channels. If there is no signal change in
the normally closed contact after the set switchover time (see technical specifications), the
module reports a diagnosis.
Purpose of changeover contact diagnostics
You can use the diagnosis for the following:
• A diagnosis of the sensor
• To make absolutely sure that there has been a switchover between a normally open
contact and normally closed contact
Principle of changeover contact diagnostics
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 validity check is negative, the following applies:
• The module identifies the value status of the normally open contact channel as "invalid".
• The module creates a diagnostic entry for the NO contact channel.
• The module triggers a diagnostic interrupt.
The digital input signal and the value status are only updated for the NO contact channel
(channel 0 and 2). In the case of the NC contact channel (channel 1 and 3) the digital input
signal is fixed at "zero" and the value status is "invalid" because this channel is only used for
a validity check of the sensor.
Note the following points when carrying out a diagnosis for a changeover contact sensor
type:
• 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. The
diagnosis for changeover contact errors continues to be carried out on the second
channel.
• You will find additional points to note in the following table:
Table 3-4 Diagnosis for changeover contacts
Changeover contact A negative check means...
Changeover contact as
NAMUR
• Short circuit or
• Wire break
Closed changeover contact
• Defective sensor or short circuit
No distinction can be made here between a defective sensor
and short circuit
Open changeover contact Caution: No distinction possible between
• Signal "0" and wire break
• Signal "1" and short circuit
Additionally:
Changeover contact error
or external fault (in the
case of DP diagnosis)