Instrumentation system

design

ECE211

Need of instrumentation

• Modern industry relies heavily on automation for

economy and mass production. With the advent of

new processes and increased automation in industry

the precise measurement and control of various

parameters is of paramount importance. Hence

industrial production goes hand in hand with

instrumentation.

• Instrumentation is that branch of engineering which

deals with measurement and control of large number

of variables embracing the disciplines of physical

sciences like physics and chemistry, and engineering

disciplines like electrical, mechanical, electronics,

communication, computer, chemical etc. It may be

treated as a multi disciplinary branch of engineering.

Instrumentation

• Technology of measurement
• Instrument : a device or mechanism

used to determine the present value or
the quatity under measurement.

• Measurement is the process of

determining the amount or degree by
comparison with the accepted
standards of the system units being
used.

A Laboratory Instrument

may have

• Some thing as an input – Input Signal from user

1. Voltage / Current,
2. Speed, Colour, Light
3. Conductivity.

• Some thing to work with this input – Processing

1. Amplify,
2. Filter,
3. Convert to other form.

• Some output – End product back to user

1. Display end result,
2. Control some device,
3. Make it available for other instrument.

Laboratory Instrument –

overview

• Electrical – Oven, Furnace, Water bath
• Optical – Microscopes, Spectrometer
• Electronic – Signal generator, Multimeter, CRO,

Power supplies, Frequency Counters, Stabilizers,

UPS

• Opto-Electronic – Lux(Light) meter, Colorimeter
• Chemical – pH meter, Conductivity meter, Water

quality Analyser

• Analytical – Spectrophotometer, Flame

photometer

• Other – OHP, X-Y Recorders, Experimental Gadgets

Performance

Characteristics

1. Static : The characteristics involved in the
measurement of quantities that are either
constant or slowly varying with time.

2. Dynamic: The characteristics involved in
the measurement of quantities that fluctuate
with time.

Static characteristics

• Accuracy: It is defined as closeness with which an

instrument reading approaches true value of

quantity being measured.

• Precision: It is measure of the degree of

agreement within group of measurement.

• Sensitivity: This is ratio of the magnitude of

output signal or response to input signals being

measured.

• Resolution: The smallest change in the measured

variable to which an instrument will respond.

• Static errors: It is defined as difference between

the measured value & true value of the quantity.

Difference between accuracy

and precision

Error

• Diffence b/w the expected value and

measured vlue of the variable.

If,

True value or expected value, Y

n

Measured value, X

n

Absolute Error, e = Y

n

- X

n

%error = (Absolute value/expected

value) *100

Types of error

• Static Error

1.Gross Error:

improper use of instrument, Inst. Change ambient

conditions when connected into a complete ckt.

2. Systematic Error:

due to shortcomings of instruments (defective,

ageing or env effects)

i) Instrumental Error:

b’coz of there mechanical structure

ii) Environmental Error:

change in humidity, temp., magnetic or

electrostatic fields

iii) Observational Error:

introduce by observer. (Parallax

error and error of estimation)

3. Random Error:

due to unknown causes. Are small and follow the law

of

probability