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Siemens TX-I/O™ Module system – Functions and operation CM110561en_08
Building Technologies Digital output functions 2018-10-25
5.2 Maintained contact, switchover
(BO Relay NO / NC 250V / Q250)
On/off switching of a wide range of devices and loads, e.g.:
– Power contactors
– Relays and semi-conductor relays
– Motors
– Burners (control loop)
– Chillers and heat pumps (control loop)
– Magnetic valves
– Display units and audible indicator units
– Step switches, pulse switches, bistable relays
• The function requires one I/O point
• The TX-I/O relay modules have changeover contacts
By use of a normally-closed contact, a closed contact can be forced even if the relay
is de-energized.
Process value
I/O status LED
Relay
Active
Inactive
On
Off
10561D01
Active
Inactive
The signal operation can be selected: Relay (Default), Relay_NA
In the case of bus failure, with DC 24 V module supply available, the following backup
states van be parameterized:
– No (Inactive) (= default)
– Value (Active, Inactive)
– Keep Same value as before the bus failure
Parameterization can be done during operation.
• Pressing the override button in the middle enables/disables the local override.
The yellow override status LED indicates that local override is active
• When local override is active:
Pressing "+" sets the process value to "Active"
Pressing "–" sets the process value to "Inactive".
• Local operation can be disabled in the configuration.
It is not admissible to couple several BOs of type Q250 to one multistate output
in the bus master. Reason: local override or each single I/O point is possible,
which may create hazardous situations. Use a multistate signal type instead,
where the outputs are electronically latched in the module.
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