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Siemens  TX-I/O™ Module system – Functions and operation  CM110561en_08 
Building Technologies  Digital output functions  2018-10-25 
Overview: behavior in case of a fault 
 
Signal type TRA  Signal type 
Response in the following 
cases 
–  No address key  
–  Powerdown 
–  Masterdown,  
integration via P-bus BIM 
Response in the following case 
–  Masterdown,  
direct island bus integration  
 
Behavior when 
fault has been 
cleared 
BO Relay NO 250V  
BO Relay NC 250V
 
The relays are de-energized 
*) 
The behavior can be parameter-
ized: the relays are de-energized, 
keep the last position, or take a 
parameterized state. 
operation: 
operation according 
to process value 
 
Tool override or 
local override: 
Operation in the 
same state as 
before the fault (the 
commanded value is 
saved in the module 
 
 
 
-- 
The Triacs are de-energized 
The behavior can be parameter-
ized: the triacs are de-energized, 
keep the last position, or take a 
parameterized state. 
 
(Schrittschalter, 
Stromstossrelais, 
bistabiles Relais) 
 
Q250 
The relays are de-energized 
*) 
The switch status of the 
power contactors is 
maintained (step switch). 
The behavior can be parameter-
ized, BUT: Do NOT parameterize 
"Keep" or "ON", as only pulses 
are needed for step switches / 
bistable relays 
 
 
-- 
Behavior can be parameterized, see section 5.4 
Q250A-P 
The relays are de-energized 
*) 
The switch status of the 
power contactors is 
maintained (due to self-
latching or dual coil relay) 
parameterized,  
The relays are de-energized 
The relays are de-energized 
*) 
The switch status of the 
power contactors is 
maintained by means of self-
latching. 
The behavior can be parameter-
ized: the relays are de-energized, 
keep the last position, or take a 
parameterized state. 
The relays are de-energized 
*) 
The switch status of the 
power contactors is 
maintained by means of self-
latching. 
The behavior can be parameter-
ized: the relays are de-energized, 
keep the last position, or take a 
parameterized state. 
-Pos Triac  
The actuator keeps its last 
position. 
The behavior can be parameter-
ized: the actuator goes to 0%, 
keeps the last position, or goes to 
a parameterized position. 
The Triacs are de-energized 
The behavior can be parameter-
ized: the signal goes to 0 %, 
keeps the last position, or takes a 
parameterized state. 
Blind Relay  -- 
The relays are de-energized 
The behavior can be parameter-
ized: all outputs are de-
energized, the last command is 
completed, or the blind goes to a 
parameterized position. 
Additionally a time delay can be 
set. 
 
*)  When using a normally-closed contact, a closed contact can be forced even if the 
relay is de-energized.