Graphical Method: FOPDT to Step Test

Dynamic processes are often characterized by a gain `(K_c)`, time constant `(\tau_p)`, and sometimes dead-time `(\theta_p)`. Use a graphical fitting method to estimate the three characteristic parameters of the following dynamic systems described by a first-order linear system with time delay.

$$\tau_p \frac{dy(t)}{dt} = -y(t) + K_p u\left(t-\theta_p\right)$$

For unstable or oscillatory responses, the first order linear equation does not represent the input to output relationship in the data. Indicate any system responses that are not a good fit for this equation form. Follow the following steps when fitting the parameters `K_p, \tau_p, \theta_p` to a step response.

  1. Find `\Delta y` from step response
  2. Find `\Delta u` from step response
  3. Calculate `K_p = {\Delta y} / {\Delta u}`
  4. Find `\theta_p`, apparent dead time, from step response
  5. Find `0.632 \Delta y` from step response
  6. Find `t_{0.632}` for `y(t_{0.632}) = 0.632 \Delta y` from step response
  7. Calculate `\tau_p = t_{0.632} - \theta_p`. This assumes that the step starts at `t=0`. If the step happens later, subtract the step time as well.

Problem 1

Problem 2

Problem 3

Problem 4

Problem 5

Problem 6

Problem 7