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
5.10 PWM Pulse width modulation
(BO PWM, with triac)
Open/close modulating actuators e.g. for
– Thermal valve actuators
– Continuously controlled consumers (e.g. electric heating controlled via current valve)

Remember to check the permissible switching frequency of the connected
devices and adapt output parameterization.
• Only TXM1.8T module supports this function
• The function uses one I/O point
• AC 24 V supply, the triac closes the contact to ⊥ (system neutral)
• Technical data (max triac load): See module data sheet N8179
• The outputs work noise-free
The function converts the analog process value AOValue to a periodic switching pulse
of the triac.
Normally, pre-parameterized outputs are used customized to the actuators to be
operated.
The following parameters are available for individual parameterization:
Parameter
Description
Value range
Default
Increment
TimePeriod Switching cycle
(0 = Special behavior)
0…6553.5 s 20 s 0.1 s
MinOnTime Min. switch-on time
– Protection against excessive switching
frequency
– Preheating ensures that the thermal
actuators open quickly
0…25.5 s
(1...25.5 s, if
TimePeriod = 0)
1 s 0.1 s
MinOffTime Min. switch-off time
– Protection against excessive switching
frequency
– Ensures that the thermal actuators close
safely
0…25.5 s
(1...25.5 s, if
TimePeriod = 0)
1 s 0.1 s
BackupMode
Backup state in the case of Masterdown Keep
No
Value
No
AOBackup
Value
Pulse duration 0.00…100.00% 0 % 1/100 %
These parameters allow for generating the following pulse patterns.
The analog output AOValue generates the following switch-on ratio (scan ratio)
OnPeriod = AOValue * TimePeriod
TimePeriod
t
OnPeriod
Min. switch-on/-off times can be parameterized as an option to protect against
excessive switching frequency. The triac does not switch on/off if the calculated switch-
on / switch-off time is less than MinOnTime / MinOffTime.
Application
Hardware
Function
Parameterization
Pulse pattern
Case A: TimePeriod ≠ 0