Redpitaya PID units and tuning

[plauria]

The units on the controller are counts. The problem is I'm trying to use the Ziegler-Nichols (http://en.wikipedia.org/wiki/Ziegler%E2 ... ols_method) tuning method for my system, but I measure the actual period in microseconds. I need to have some correspondence between a physical time and the counts.

I.e. essentially I set the integrator and derivative gain to zero. I bring the system into oscillation using proportional gain, Kp=4300. The period was P was measured at 2.6 microseconds. Then 'in theory' the integral gain is just .6*2Kp/P. But 2.6 microseconds has units; the gain does not. What should I do here? Can I just divide by this time by input clock rate (1/(125 MHz))?