ALevel-CS 07

Monitoring and control systems

7.01 Monitoring systems

Monitoring systems

These systems require a measuring device that records a value which can be transmitted to the computer. Such a measuring device is a called a sensor.

It is important to understand that in a monitoring system, a sensor does not have any built-in intelligence, so it cannot take any action if there is a problem. If the temperature measured becomes dangerously high it is the computer that sounds an alarm.

sensors:

pressure, humidity, carbon monoxide, pH, sound.
infrared sensor
motion sensor

7.02 Control systems

Key Terms

Sensor - a hardware device that measures a property and transmits a value to a controlling computer
Actuator - a hardware device that receives a signal from a computer and adjusts the setting of a controlling device

Control systems

A control system has the monitoring activity plus the capability to control a system.

ADC - analogue-to-digital converter

DAC - digital-toanalogue converter

If the measurement value received by the computer is not in the desired range the computer initiates a control action. The next timed measurement will happen after this control action has taken place. In effect this next measurement provides feedback to the computer on the effect of the control action. Feedback is essential in a control system.

A closed-loop feedback control system is a special type of monitoring and control system where the feedback directly controls the operation. A microprocessor functions as the controller. This compares the value for the actual output, as read by the sensor, with the desired output. It then transmits a value to the actuator which depends on the difference calculated.