It is the best PPT for agricultural engineering students to study agricultural instrumentation course

1. AE23001
Agricultural Instrumentation
Anubhab Pal
North Eastern Regional Institute of Science and
Technology
Nirjuli – Arunachal Pradesh

2. Lecture 1
• Learning objectives
1. Basics of measurement system and measuring units
2. Instrument error and accuracy
3. Basic structure of measuring instrument

3. Measurement system
Acceleration Density
Velocity Viscosity
Displacement Composition
Force–Weight pH
Pressure Humidity
Torque Temperature
Volume Heat/Light flux
Mass Current
Flow rate Voltage
Level Power
Measurement system
Process
Information
Information variables
Observer

4. Units for measurement
• Purpose
• Quantifies the measured variable
• System of units
• Traditional. e.g. hand for length.
• Imperial. e.g. inch for length.
• SI (Système international d'unités) e.g. meter for length
• Others. e.g. CGS, FPS, MKS etc.
• Base/ fundamental unit. e.g. second for time
• Derived unit. e.g. Newton for force (kg.m/s2)

5. Units for measurement

6. Units for measurement

7. Necessity for using proper units
Loss of MARS Climate Orbiter (MCA)
• MCA should to enter orbit at an altitude of 140.5–150km
(460 – 500 k ft.)
• It entered orbit at 57 km (190,000ft.) and was destroyed
Reason:
• The contractor for the craft's thrusters did use English
units.
• NASA did use SI units.
• Instead of 150000 m the craft was set to a target altitude
of 150000 ft.

8. True vs. measured value
Measurement
system
Process True value of
variable(s)
Input
Measured value of
variable(s)
Output
𝑇𝑟𝑢𝑒 𝑣𝑎𝑙𝑢𝑒 − 𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑣𝑎𝑙𝑢𝑒 = 𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑚𝑒𝑛𝑡 𝑒𝑟𝑟𝑜𝑟 (𝐸)
Accuracy
It is defined as the closeness of the measured value to
the true value.

9. Structure for measurement
systems
• There are basically four elements in any
measurement system.
• Sensing element
• It is in contact with the process.
• It provides output as a function of the variable to be measured.
• Examples,
• Thermocouple where millivolt e.m.f. depends on temperature.

10. Structure for measurement
systems
• Signal conditioning element
• Takes the output from the sensing element into a more suitable
form for further processing.
• The output of the signal conditioning element is generally DC
voltage, DC current or frequency signal.
• Examples,
• Amplifier which amplifies millivolts to volts.
• Signal processing element
• The output of signal conditioning element is fed to signal
processing element which converts it into a form more suitable
for presentation.
• Examples,
• Analogue-to-digital converter (ADC) which converts a voltage
into a digital form for input to a computer.

11. Structure for measurement
systems
• Data presentation element
• This element presents the measured value in a form which
can be easily recognized by the observer.
• Examples,
• Simple pointer–scale indicator.
• Alphanumeric display.
• In addition to these four components, some
measurement systems have signal transmission
element to transmit the signal to some remote point.
• Signal transmission is needed when the observation or
application point of the output of a measurement system is
some distance away from the site of the primary transducer.

12. Classification of types of
measurement systems
1. Monitoring process and applications
• Used where measuring device is used to keep track of some
quantity.
• They simply indicate the condition of the process variables.
• Their readings do not serve any control functions in ordinary
sense.
• Example,
• Speedometer, odometer, fuel gauge in vehicles, thermometer etc.
2. Experimental engineering analysis
• Example,
• Lab testing of a machine.

13. Classification of types of
measurement systems
3. Control processes and operations
• This usually refers to an automatic feedback control system.
• In this type of operation, the ‘control variable’ is measured,
compared in a ‘controller’ with a desired value.
• Based on the ‘error’, the final control element is manipulated to
drive the control element closer to the desired value.
• Example,
• Temperature control of room air conditioner, engine governor etc.
Process
Final control element
Controller
Measuring instrument
Input energy and/or material Controlled variable
Disturbances
Desired value of controlled variable

14. Selection of appropriate
measurement systems
• Desired measurement accuracy, resolution, sensitivity
and dynamic performance etc.
• The environmental conditions that the instrument will be
subjected to.
• The extent to which the measured system will be
disturbed during the measuring process.
• Cost (Initial and running)

15. Thank you
End of Lecture 1