640-381: Principles and Applications of Sensors

 

Problem Sheet 1:

 

  1. How is the sensitivity of a sensor defined?

 

  1. What is the difference between precision and accuracy of a sensor?

 

  1. What is the difference between and active and passive sensor?

 

  1. Is there a difference between a transducer and a sensor. Give examples of each.

 

  1. How is the time response of a sensor to a changing stimulus characterized?

 

  1. Give an example of a sensor which responds quickly to an increase in stimulus, but slowly to a decrease.

 

  1. Define the following terms:

 

    1. Hysteresis
    2. Dead band
    3. Saturation

 

  1. List some environmental factors which may affect sensor performance

 

 

9.  The capacitance of cylinder of height H partially immersed in liquid is:

 

C = 2 p e 0 [ H - h (1 - k ) ] / ln b /a

 

Here b is the outer diameter of the cylinder, a is the inner diameter, k is the dielectric constant of the liquid in which the cylinder is immersed and h is the level to which the cylinder is immersed in the liquid (ie h=0 is completely out of the water, h=H is completely immersed.

 

a) If h  = 2 cm, H = 20 cm, e 0 = 8.85 10 -12 C 2 /Nm 2,  a = 1 mm,

b = 2 mm, k (water) = 78.5, what is the capacitance of the cylinder?

 

b) How different is it to the value when the sensor is out of the

water?

 

c) The sensor is to be used to measure the height of fluid. Discuss the performance  of this sensor for this purpose. Is the transfer function linear? Is the sensitivity the same regardless of the fluid height. Give an expression for the sensitivity.

 

d) Is the sensor performance independent of what fluid it is immersed in? For example, how sensitive would this  coaxial level sensor if it were used to detect the level of transformer oil [k(oil)= 4.5)] instead of water.