Feedback control requires being able to sense the variable being controlled. Because electrical signals can be transmitted, amplified, and processed easily, often we want a sensor whose output is a voltage or current proportional to the variable being measured. Describe a sensor that would give an electrical output proportional to:

a. Temperature
b. Pressure
c. Liquid level
d. Flow of liquid along a pipe (or blood along an artery)
e. Linear position (t) Rotational position
f. Linear velocity
g. Rotational speed
h. Translational acceleration
i. Torque

A thermocouple is made of two different metals which are joined together creating a junction. Whenever there is a change in temperature, a voltage is produced at the junction which is proportional to the temperature that is being measured.

b. Pressure

Pressure sensor or Strain Gauge or Load Cell

The basic principle behind these sensors is that the pressure change is basically a change in force which changes electrical resistance proportional to the applied force.

c. Liquid level

Linear Variable Differential Transformer (LVDT) coupled with some mechanical parts.

d. Flow of liquid along a pipe (or blood along an artery)

Any pressure sensor would work

e. Linear position

LVDT

Linear Variable Differential Transformer is a robust and cheap transducer that works on the principle of a normal transformer that is electromagnetic coupling. It can measure position as well as displacement

(t) Rotational position

RVDT

Rotary Variable Differential Transformer is a modified type of LVDT that measures rotational positional or displacement.

f. Linear velocity

Speedometer

The working principle behind speedometer is simple electromagnetism. A rotating magnet produces magnetic field which induces voltage proportional to the speed.

g. Rotational speed

Tachometer

It measure the rotation of shaft usually in revolutions per minute (RPM). it produces output voltage proportional to the speed of the moving shaft.

h. Translational acceleration

LVDT

i. Torque

Tachometer with Gear