Feedback Energy In Do Modules; Calculation Of Feedback Energy - Emerson PACSystems RSTi-EP User Manual

User Manual
GFK-2958J
3.8
Feedback
With digital output modules, power is fed back through the channels when inductive loads
are switched off. The respective permissible breaking energy is noted in the technical data
of the DO modules. Depending on the switching frequency, the breaking energy leads to
additional energy loss in the output module.
If the maximum permissible feedback energy for a module is exceeded, the module shuts
down temporarily.
Note:

Calculation of Feedback Energy

The feedback energy for a digital output module can be calculated as follows:
P = Σall channels 1/2 ni * Li * Ii²
where
P =
n =
i
E =
i
I =
i
L =
i
Once the maximum permissible feedback energy E
Figure 16: Maximum Feedback Energy Varies with Ambient Temperature
Configuration
Energy in DO Modules
Feedback energy can be prevented by installing external freewheeling protection. With it, the same
switching rate can be achieved with an inductive load as with a resistive load.
Feedback energy of the module
Switching cycles of Channel i in 1/seconds
Feedback energy when shutting off Channel i during a shutdown procedure
Current through the load connected to Channel i
Inductance of the load connected to Channel i
is reached, the module shuts down.
max
Chapter 3
Oct 2019
30