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NI 9758 User Manual
Driving High Impedance Injectors
High impedance injectors may be used with the PFI driver circuits without any hardware or
software configuration changes. High impedance injectors will have approximately 12
Ω
resistance across the solenoid. Typically, less than 1 A is required to open and hold the solenoid
valve.
High impedance injectors require a single current phase. Set the duration of the first phase to
zero to keep control of the phase during the injection event.
The open circuit flag should be ignored when driving high impedance injectors because the hold
current level of 1 A may never be reached, thus reporting a false open circuit.
Short circuit detection operates identically to that of low impedance injector control and the
channel will be disabled if a short is detected, until the error flag is cleared in software. Even
though the short circuit detection and disable feature is present, it is strongly recommended that
the wiring harness include a 5 A automotive fuse for four high impedance injectors.
Figure 3.
Hold Current Reached and Controlled
Figure 4.
Hold Current Never Reached
Caution
Do not attempt to drive low impedance injectors with the general purpose
low-side switch drivers. The low-side drivers are only rated for 1.2 A continuous. The
resulting higher current levels could damage the low-side drivers.
