Theory
There are 2 main types of systems: open loop systems and closed loop systems. In closed
loop systems, there is a feedback from the output that can be used in error calculation,
while in closed loop systems there is no feedback. The feedback in closed loop systems can
be either positive or negative, but negative feedback systems are more commonly used (the
input and the output are compared). The feedback is used to account for any disturbance in
order to adjust the output. The measured output is redirected to the controller to account
for any disturbance at the summing junction. This used in error calculation where the actual
output is subtracted from the input. This process is repeated until the error is minimized.
In open loop systems, a specific set point is chosen, and the output is obtained, but as
mentioned earlier, open loop systems have no feedback, so any disturbance will significantly
affect the output. This a significant disadvantage of open loop systems.
Figure 1: open loop vs closed loop
There are many types controllers such as PI (proportional-integral), PD (proportionaldifferential), PID (proportional-integral-derivative), lead controllers, lag controllers and leadlag controllers.
During the experiment, calibration is done by measuring the temperature of hot and cold
water. This is followed by finding the slope of the graph of the thermocouple using 𝑎 =
𝑚𝑇 + 𝐶 where a is the voltage, m is the gradient, T is the temperature and C is the yintercept.
For the open loop part, the temperature is measured at 60 second intervals and the graph is
plotted using the obtained temperature. The experiment is repeated after adding the P
compensator, but the temperature is measured every 30 seconds and the graph is plotted.