Operating Instructions

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Siemens TX-I/O™ Module system – Functions and operation CM110561en_08
Building Technologies Digital output functions 2018-10-25
5.3 Maintained contact, triac (BO Triac NO / NC)
On/off switching of AC 24 V devices, especially:
– Frequent switching (triacs do not have any problems with contact life span)

However, check the admissible switching frequency of the connected
device and adjust the parameters or the application accordingly.
– Other devices with AC 24 control
– silent switching
• The function is supported by module type TXM1.8T only.
• The function requires one I/O point.
• The supply is AC 25 V, the triay closes the contact to ⊥ (system ground).
• Technical data (max. output of the triacs): see data sheet N8179.
Process value
I/O status LED
Relay
Active
Inactive
On
Off
10561D01
Active
Inactive
The signal operation can be selected: Triac (Default), Triac_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 runtime.
• The I/O status LED is ON when the triac is active, i.e. when the N/O contact is
closed and the N/C contact is open.
• In the event of an error, the I/O status LED and the module status LED flash.
For details, especially in relation to flashing pattern and errors: refer to the section "Dis-
play, operation and diagnostics" in the TX-I/O™ Engineering and installation guide [6].
TXM1.8T has no local override.
The quality value "No_Output" is sent when AC 24 V is absent.
In this case the triac can not be activated  the module switches the output off and
sets the process value to 0.
The fault message is only sent when a command is pending.
Application
Hardware
Function
Parameterization
Display
Local override
Fault message