Transcript 01-1-Sensitivity-Resolution-and

Sensitivity, Resolution and
Error
Prepared By :
• Hani Mohammad Kharraz (0115176)
• Yazan Daifallah Abawi (0118468)
Sensitivity:
Definition
 Sensitivity is an absolute quantity, the smallest absolute amount of change
that can be detected be an instrument.
 Sensitivity of measurement can be defined as the change in instrument
output that occurs when the quantity being measured changes by a given
amount.
 Therefore, sensitivity can be expressed as the following ratio:
𝑆𝑐𝑎𝑙𝑒 𝐷𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛
𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑚𝑒𝑎𝑠𝑢𝑟𝑎𝑛𝑑 𝑝𝑟𝑜𝑑𝑢𝑐𝑖𝑛𝑔 𝑑𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛
 The sensitivity may be constant or variable along the scale
Sensitivity:
The sensitivity of measurement is therefore the slope of the straight
line
Sensitivity:
for example:
A pressure of 2 bar produces a
deflection of 10 degrees in
a pressure transducer
the sensitivity of the instrument is 5
degrees/bar
10
= 5 𝑑𝑒𝑔𝑟𝑒𝑒𝑠 𝑏𝑎𝑟
2
Sensitivity:
 For the following data, Determine the measurement sensitivity of the
instrument in ohms/°C
 For a change in temperature of 30°C, the change in resistance is 7
7
= 0.233 Ω °𝐶
30
Increasing a systems sensitivity
 When you design a system you need to account for all eventualities.
 A likely problem you will have is that the system you are controlling will not
stay the same.
 Every system you ever try to control will have changes. If you design for
some nominal case and don't account for the variability of the system, you
could have a system that is unstable for some commonly encountered
situation.
Resolution:
Definition
 Resolution can be defined as the degree to which a change can be
detected.
 It can also be defined as the smallest possible magnitude of the change in
the input measured quantity that produces an observable change in the
instrument output.
Resolution:
Definition
 In order to determine the resolution of a system in terms of voltage, first we
determine the voltage span
 For example a voltmeter that measures from -10v to +10v has a voltage
span of 20v
 And then we determine the smallest possible change that can be
detected
 Resolution is sometimes specified as an absolute value and sometimes as a
percentage
 One of the major factors influencing the resolution of an instrument is how
finely its output scale is divided into subdivisions
A car speedometer for example has a division of 20 Km/h and
so we cannot estimate speed more accurately than to the
nearest 5 Km/h.
This figure of 5 km/h thus represents the resolution of the
instrument.
Error :
Definition
 The error in measurement is a mathematical way to show the uncertainty in
the measurement.
 It is the difference between the result of the measurement and the true
value of what you were measuring.
 For example, If you measure the same object two different times, the two
measurements may not be exactly the same.
 Errors in analogue instruments (which use pointers) is greater than digital
instruments.
Types of Errors :
1. Assembly Error : Errors due to improper manufacturing
of the instruments.
A. Displaced scale : The incorrect fitting of zero scale with respect to the
actual zero position of the movement.
B. Non-uniform scale: When the scale of the measuring instrument is not
divided uniformly. In some part of the scale the markings may be too close
and in other parts too far .
C. The pointer is bent : The pointer may get bent in either horizontal direction
or the vertical direction, in either case, is shows erroneous reading.
D. Manufacturing errors in the components :The instruments are made up of a
number of small components, which may be manufactured in different
places. Sometimes there are manufacturing errors in some of these
components
2. Environmental Errors
 The measuring instruments are designed to be used in within certain
restricted conditions, but when they are used in different conditions, there
are errors in measurement .
 This kind of errors is highly unpredictable.
 These errors can be sometimes positive, sometimes negative and
sometimes combination of the both.
some precautions to be taken to reduce
the environmental errors in the instruments:
1. Use in the instruments within the specified limits of temperature, pressure
and humidity for which the instrument has been designed.
2. If you have to use the instrument beyond the specified limits
of environmental conditions, then apply suitable corrections to the
recorded measurement.
3. One can also calibrate the instrument newly in the new conditions.
4. There are some devices that enable applying the compensation
automatically.
3.Random Errors
A. Frictional errors : Due to moving mechanical parts in the analogue
measuring instruments.
B. Mechanical vibrations : When the instrument is used in vibrating place the
parts of the instrument start vibrating giving faulty readings.
C. Hysteresis of the elastic members : Over the period of time the elastic
members tend to loose some elasticity leading to errors in the indicated
value of the instrument.
D.
Finite scale divisions : The scale marking can be made only up to certain
limits.
4.Parasitic Errors
A. Error of Method
B. Observation Error
C. Parallax Error : When there is a big gap between the scale and pointe.
D. Misalignment Error
Misalignment Error
Parallax Error