dPID: The dPID class

status:

RC-1.0

This article shows the dpid.PID documentation, as specified in the python file.

It specifies the interface to a discrete-PID-controller. Study it to understand how the class should be used. Then start writing python code to test it.

Attention

Its’ a python-coding exercise

When part of this controller is 100% clear, just assume it is working correctly. And fill in the details as needed. Use that as base for your test-code.

• At least, eventually, the class and the code are consistent. So, future changes will not invalidate current (assumed) behaviour; without notice.

• During normal development, such details should be incorporated into the doc-string; possible after discussion and/or approval

• For the ‘homework-goal’ the exact working isn’t that relevant. Fill in details as needed; focus on writing python-code!

class dpid.dPID(P, I, D, min_result=None, max_result=None)

A simple discrete-PID controller, as an exercise.

This PID-controller can be initialised with constantes for P, I and D; which can’t be changed afterwards. Optional, a minimum and maximum output value can be given; both during initialisation, and later.

The controller has two inputs: setpoint() and measured(), and one output: result(). Those inputs can be set/updated independently. Similarly, the result() can be read at any-moment. As the controller will remember the timestamp a values changes (and knows when the result is read), it will always give the correct output. Thus, that output value does depend on the timestamp it is requested!

The setpoint() is considered as a step-function: between two changes, it will remain the last value. The measured() value however should be considered as a continuously linear-changing value. So, between two updates of this value, the dPID-controller will interpolate linearly.

When a result() is read during such a period; the PID-controller can’t predict the next-measured-value, however. Therefor, it will (for that single read) assume the measured-value is the same as last-time.

When a maximum and/or minimum value is set, the result() will be clipped to that value when needed. Without a min/max, the result() is unlimited.

Hint

As this class is part of an exercise; no implementation is given.

During the training one should update this file to implement the class without changing the interface.

All (numeric) input & output values are either integers or floats.

setpoint(sp)

Set the setpoint: a numeric value.

measured(value)

Give the controller an update on the actual measured (or simulated) process-value.

The controller will assume a linear progression between the last update and the current one

result()

Return the actual result value

set_min_max(min_result=None, max_result=None)

Change the minimum and/or maximal result value. Used to clip the result()

Comments

comments powered by Disqus