Functional elements (1)

Functional elements (1)

1. FUNCTIONAL ELEMENTS OF
MEASUREMENT SYSTEMS

2. Measured
Medium
Measured
Primary
sensing
element
Variable
conversion
element
Variable
manipulation
element
Data
presentation ,record,
transmission element
Functional elements
of Measurement Systems
Ⅰ. Functional Elements
PRIMARY
SENSING
ELEMENT

3. Basic components in a measurement system are shown below:
It is also important to mention that a power supply is an
important element for the entire system.
Amplification and Conditioning

4. Complete measurement system
Instrumentation is the science and
technology of complete measurement
systems with which physical quantities are
measured so as to obtain data which can
be transmitted to recording and display
devices.

5. Transducers -The primary sensing
element
The primary sensing elementis that which first receives
energy from the measured medium and produces an
output depending in some way on the measured quantity
(“measurand").
It is important to note that an instrument always extracts
some energy from the measured medium. T
The measured quantity is always disturbed by the act of
measurement, which makes a perfect measurement
theoretically impossible. Good instruments are designed to
minimize this effect, but it is always present to some
degree.

6. Transducers
A.Definition
“Any of varies substances or devices that convert input energy of
one form into output energy of another.”
i.e. : mechanical energy mechanical energy
Ex: Linear Motion Rotational Motion

7. Measurement System
Conversion

8. The variable-conversion element
The output signal of the primary sensing element is
some physical variable, such as displacement or
voltage.
For the instrument to perform the desired function.
it mavbe necessary to convert this variable to
another more suitable 'suitable while preserving
the information content of the original signal.
An element that performs such a function is called
a variable-conversion element.
Not every instrument includes a variable-
conversion element, but some require several.
The “elements" are functional elements, not
physical elements,

9. Conversion of resistance to voltage or
current change
Use a bridge circuit

10. Signal Conditioning /Processing
The output of a transducer may have to be
altered to make it suitable for
transmission
display
recording

11. The variable-manipulation element
An instrument may require that a signal represented by
some physical variable be manipulated in some way.
Manipulation --a change in numerical value according to
some definite rule but a preservation of the physical nature
of the variable.
Thus an electronic amplifier accepts a small voltage signal
as input and produces an output signal that is also a
voltage but is some constant times the input. An element
that performs such a function is called a variable-
manipulation element,
A variable-manipulation element does net
necessarily ,follow a variable-conversion element, but may
precede it, appear elsewhere in the chain, or not appear at
all.

12. Processes involved
Signal level
change -amplification
or reduction
Linearization
Conversion of a
change in resistance to
a variation in voltage or
current
Filtering
Impedance matching
A/D conversion

13. Signal conditioning
“Signal Conditioning” is the manipulation of the
output of a sensor, probe, or transducer to
perform one or more of these functions:
•Amplification
•Attenuation
•Filtering
•Linearization
•Signal conversion

14. Signal Conditioning
Attenuation and Amplification

15. Signal Conditioning
To minimize input resolution error (quantization error), the input to the A/D
converter should utilize the full range of the A/D converter (e.g. +/-10 volts).
If our input signal is in the range of +/-10 mV (a microphone signal), we
would want to increase this signal to bring it into the range of our A/D…
(amplification)
If our input is in the range of +/-100 V (power line signal), we would
want to decrease this signal to bring it into the range of our A/D…
(attentuation)

16. Signal Conditioning
There are several ways that a signal can be
attenuated. We’ll talk about one of those tomorrow.
For a signal to be amplified, there needs to be an
active source of power placed in the circuit.
Such an active source might be an operational amplifier
(Op Amp).

17. The data-transmission element
When the functional elements of an instrument are
actually physically separated, it becomes necessary
to transmit the data from one to another.
An element performing this function is called a data-
transmission element.
It may be as simple as a shaft and bearing assembly
or as complicated as a telemetry system for
transmitting signals from satellites to ground
equipment by radio

18. The data-presentation element.
If the information about the measured quantity is to be
communicated to ahuman being for monitoring, control, or analysis
purposes, it must be put into a form recognizable by one of the
human senses.
The element that performs this “translation" function -data-
presentation element.
This function includes the simple indication of a pointer moving over
a scale and the recording of a pen moving over a chart,
Indication and recording also may be performed in discrete
increments (rather than smoothly),
While the majority of instruments communicate with people through
the visual sense, the use of other senses such as hearing and touch
is certainly conceivable.

19. Display Systems
Analogue meter
◦Simplest system -pointer and scale.
◦Use for at a glance readings
◦Use for monitoring limits -use colours
◦Use for tuning to maximum or minimum preset limits.
◦Cheaper than digital -but less so all the time as
electronics become cheaper.
◦The input signal may need to be amplified or reduced
to give a direct reading
◦Can follow the direction of changes easily

20. Display Systems
Digital meter
Best when numerical value required
Compare the use of a vernier calliper with a similar
device with a digital display.
Don't assume that resolution = accuracy
The input signal may need to be amplified or reduced
to give a direct reading
Note: Analogue and digital direct reading meters are
suitable only for signals varying in times > 0.1s -why?

21. Display and Recording Data
Decided by the purpose of the measurement.
If the measurement is used by the operator to check
if the value is within specified bounds, a simple
visual display is required.
If the measurement is to enable a value to be set at
a specified value, a digital display is best.

22. Display and Recording Data
For 100% inspection of components on a production
line, data may be
printed on printer
displayed on a VDU
stored in a computer
plotted on a plotter
recorded by a computer in data files.

23. Measurement Systems
Data recording

24. The data recording
Although data storage in the form of pen/ink
recording is often employed, some applications
require a distinct data storage/playback function
which can easily re-create the stored data upon
command.
The magnetic tape recorder/reproducer is the
classical example here. However, many recent
instruments digitize the electric signals and store
them in a computer like digital memory.

25. Data Recording
Chart recorder -plots a signal against time
Various types
pen and paper
pressure stylus and pressure sensitive paper
UV recorder ultra-violet light deflected by mirror onto
light sensitive paper.
Fibre optic recorders -fibre optics direct light from a
fluorescent screen onto light sensitive paper.

26. THANK YOU