CV 178
| |||||||||
NMRA CV 178 - BEMF Sensitivity A
CV 178 can be used to configure how quickly the BEMF algorithm will react to changes Above the "Critical Speed Step" (CV 181).
Geek Speak: At higher speeds there is more motor commutation noise and pole voltage variance which injects noise into the decoders BEMF reading. By responding slower this gives smoother control by filtering out some of that noise.
The speed/RPM at which this transition occurs will vary based on the type of motor, gear ratio, etc. Usually this speed step is 7 (of 128) or below. This CV is used to set a speed step at which the behaviour of the BEMF changes. Through the use of This CV, as well as CV 179, you can set up two different levels of "responsiveness" for the BEMF algorithm. This feature is most useful with 3-pole and "coreless" motors which tend to have dramatically different BEMF swings depending on the RPM. A higher value gives a slower response time which is needed at higher speeds.
| !!!WARNING!!! This CV should not be modified unless you are trying to correct a significant issue with slow speed motor control. We do not suggest modifying this CV unless absolutely necessary. |
This "responsiveness" refers to the motor control itself, not necessarily the sound functions such as chuff intensity or prime mover RPM. Refer to our section on Prototype Throttle Mode for guidance on BEMF calibration for sound function.
| NOTE: This CV was introduced at different times in different decoders. This CV will not do anything if programmed with a value on a decoder which does not support the feature. |
Only current-generation decoders (V4.5 Diesel, V4.6 Steam, V90+ Mobile) support this CV and featureset.
