NI 9751 User Manual
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© National Instruments
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15
BackBoostTime
The BackBoostTime is a global parameter that is critical for proper solenoid injector control.
This time period directly follows the end of the injection command duration and allows the
back-emf of the injector solenoid to be directed to the internal power supply for back-boosting
the internal high voltage power supply. The BackBoostTime brings the injector solenoid current
quickly to zero. If BackBoostTime is set to zero, injector current recirculates through the injector
until the energy dissipates, which might cause unpredictable injector valve closing. Calibrate the
BackBoostTime long enough for the energy within the injector solenoid to fully discharge to the
internal boost power supply. If BackBoostTime is greater than zero, but too short, the injector
current bumps up and recirculates until the energy fully dissipates. Extend BackBoostTime until
the scope solenoid current trace can no longer display the current recirculation. A typical
BackBoostTime is approximately 0.2 ms. Injectors with higher inductance provide more energy
to dissipate at the end of injection and thus require a longer BackBoostTime. Figures 11
through 15 show different values for BackBoostTime applied to the same solenoid injector.
Figure 11.
BackBoostTime = 0.0 ms
Figure 12.
BackBoostTime = 0.025 ms
Summary of Contents for NI 9751
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