PID Control

Each channel of the NI-9470 has a hardware digital PID controller with its own set of independent coefficients. The PID controller activates when you set the channel output mode to Average Current mode.

You can set the PID controller response to Slow, Medium, or Fast, or you can use a custom response that allows you to choose any PID coefficient value. The following table shows the approximate load characteristics for the preset PID responses.

Table 3. Preset PID Responses Guidelines
PID Response Load L/R
Slow 0.02 H/Ω to 0.15 H/Ω
Medium 0.005 H/Ω to 0.02 H/Ω
Fast 0.001 H/Ω to 0.005 H/Ω

You can use the Slow PID response option with a lower PWM frequency for high-inductance loads and the Fast response option with a higher PWM frequency for low-inductance loads.

Custom PID coefficients use the unit duty cycle percentage divided by amp. For example, if the integral coefficient I = 1%/Amp and other coefficients are zero, then an error of 1 A between the current setpoint and the readback will change the PWM duty cycle output by one percent.