The main purpose of this exercise is to make a control system similar to the one from the C programming exercise. It should read the values of the induction motor current, calculate RMS and detect the overload (when RMS exceeds some given value). It should also provide self-diagnostics which make sure that data is read correctly.

Skills:

• Reading data from a file.
• Data processing.
• Handling multiple processes (watchdog) and simple message passing.

Grading: points are given in square brackets.

• Using your experience from previous labs, write a function which reads data from ac_current.dat and counts the number of samples.

• Write a function which reads data from a file ac_current.dat [2].
• Write a function which calculates the RMS value from 20 consecutive samples (in this case it is the main period of the waveform) [6].
• Make the above functions work together, displaying the calculated RMS value [3].

• Using the previous functions, write a function which reads data from a file, calculates the RMS value, checks if this value exceeds some given level x (given as an argument), and exits if it does so [4]. The function should return the number of the RMS values read before it exits [4] and the violating RMS value as well [2].

A watchdog is a process which makes sure that other processes work properly. It is often used to make sure that data from sensors is read.

Enhance your program to accommodate a watchdog.

Hints:

• Spawn a watchdog process [2].
• Make the reading function to send a message to the watchdog every time a new value is read [4].
• If the watchdog waits for a message too long it should display a message: 'Input data flow is too slow at index:' [4] followed by the index value [2].
• There should be a way to terminate the watchdog by sending it a special message [2].