TWControls said:
POf course the question always is how do you figure out how high of resolution encoder you would need?
If you are not using advanced techniques or gearing, then it depends on how much quantizing your system can tolerated on the output. To do this you must look at the PID controller. If there is no error the PID outputs no correcting signal. It there is one count of error due to quantizing then the output will change by:
Ki*T+Kp+Kd/T
or newest controller has a double derivative gain which is a gain multiplied by the error in acceleration. In this case the output changes by
Ki*T+Kp+Kd/T+Kd'/T^2
Where
Ki is the integrator gain, multiplied by the sum of position errors
Kp is the proportional gain, multiplied by the position error
Kd is the derivative gain, multiplied by the velocity error
Kdd' is the double derivative gain, multiplied by the acceleration error
T is the sample time in seconds
If 1 count of quantizing error changes the output by one 1 volt, that is too much. THERE IS NO POINT IN HAVE 16 BIT ANALOG OUTPUTS IF THE OUTPUTS ARE CHANGING BY 0.1 VOLTS.
The insanity I see over and over again is that people want 16 bit analog outputs and yet get low resolution feedback where a 6 bit analog output would do.