1. Introduction, measurement systems, classes of transducer

2. Displacement measurement, potentiometers, variable capacitor,s,LVDT

3. Temperature measurement,RTD, Thermistor, thermocouple

4. Temperature measurement and signal conditioning

5. Operational amplifier application in instrumentations

6. Stress and strain measurements

7. Vibration, acceleration, pressure and flow measurements

8. Date acquisition, A/D and D/A conversion.

9. Digital circuits: applications and realizations

10. Displays , analogue and digital.

11. PIC microcontrollers 2weeks

12. Actuators: solenoids and DC and AC motors

13. Actuators: stepper and servo motors

introduction Measurement is essentially the act, or the result of a quantitative

comparison between a given quantity and a quantity of the same kind chosen as a unit.

The device used for comparing the unknown quantity with the unit of measurement is called measuring instrument.

The value of unknown quantity can be determined by direct like current by ammeter voltage by voltmeter

or indirect (measuring other quantity related to it the calculating the desired one rather than measuring it)like resistance of a conductor(R=V/I) .

Measurement techniques have been of immense importance ever since the start of human civilization.

The industrial revolution during the 19th century brought about a rapid development of new instruments and measurement techniques to satisfy the needs of industrialized production techniques.

The massive growth in the application of computers to industrial process control and monitoring tasks has spawned a parallel growth in the requirement for instruments to measure, record and control process variables

Present-day applications of measuring instruments can be classified into three major areas(of measuring).

The first of these is their use in regulating trade, applying instruments that measure physical quantities such as length, volume and mass in terms of standard units.

The second application area of measuring instruments is in monitoring functions.

These provide information that enables human beings to take some prescribed action accordingly.

the majority of monitoring functions exist to provide the information necessary to allow a human being to control some industrial operation or process

In a chemical process for instance, the progress of chemical reactions is indicated by the measurement of temperatures and pressures at various points, and such measurements allow the operator to take correct decisions regarding the electrical supply to heaters, cooling water flows, valve positions etc.

Use as part of automatic feedback control systems forms the

third application area of measurement systems.

A measuring system exists to provide information about the

physical value of some variable being measured.

In simple cases, the system can consist of only a single unit that gives an output reading or signal according to the magnitude of the unknown variable applied to it.

The term measuring instrument is commonly used to describe a measurement system, whether it contains only one or many elements.

The first element in any measuring system is the primary sensor: this gives an output that is a function of the measurand (the input applied to it).

For most but not all sensors, this function is at least approximately linear. Some examples of primary sensors are a liquid-in-glass thermometer, a thermocouple and a strain gauge.

Variable conversion elements are needed where the output variable of a primary transducer is in an inconvenient form and has to be converted to a more convenient form.

For instance, the displacement-measuring strain gauge has an output in the form of a varying resistance.

The resistance change cannot be easily measured and so it is converted to a change in voltage by a bridge circuit, which is a typical example of a variable conversion element.

In some cases, the primary sensor and variable conversion element are combined, and the combination is known as a transducer.

Signal processing elements exist to improve the quality of the output of a measurement system in some way.

A very common type of signal processing element is the electronic amplifier, which amplifies the output of the primary transducer or variable conversion element, thus improving the sensitivity and resolution of measurement.

This element of a measuring system is particularly important where the primary transducer has a low output.

For example, thermocouples have a typical output of only a few millivolts. Other types of signal processing element are those that filter out induced noise and remove mean levels etc.

In some devices, signal processing is incorporated into a transducer, which is then known as a transmitter.

some measurement systems have one or two other components, firstly to transmit the signal to some remote point and secondly to display or record the signal if it is not fed automatically into a feedback control system.

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.

The signal transmission element has traditionally consisted of single or multi-cored cable, which is often screened to minimize signal corruption by induced electrical noise.

An analogue instrument gives an output that varies continuously as the quantity being measured changes.

The output can have an infinite number of values within the range that the instrument is designed to measure.

The deflection-type of pressure gauge is a good example of an analogue instrument.

A digital instrument has an output that varies in discrete steps and so can only have a finite number of values.

Measurement Terms SIGNAL TERM: in indicating, recording or transmitting device it is

important to know about the quantity under measurement.

i. measured variable: variable is that quantity of characteristic which is the object measurement in an instrumentation/control system

ii. Input signal: it is a signal applied to a device, element, or system such as pressure applied to the input connection of a pressure transmitter.

iii. Output signal: it is a signal delivered by a device, element or system

Range Related Term: range and span is used to describe the region over which a quantity is to be measured.

i. Range: the region between the limits with in which a quantity is measured, received or transmitted, expressed by stating the lower and the upper limits, such as 0-50A…50-500V…-20-80Co

ii. Span: the algebraic difference between the upper and the lower range value. Such as for range 0 to 50A span is 50

for range 50 to 500V span is 450V for range -20 to 80Co span is 100Co

iii. Over range: any excess value of the input signal above its upper range value or below its lower range value

iv. Low Range Limit: the lowest value of quantity the a device can be adjusted to measure

v. Upper Range Limit: the highest value of the measured variable that a device can be adjusted to measure

vi. Lower Range Value: the lowest value of the measured variable a device is adjusted to measure.

vii. Upper Range Value: the highest value of the measured variable a device is adjusted to measure.

READABILTY TERM: the fineness by which the measured variable can be observed depends on a number of factors, the length of the scale, and the number of scale graduations largely influence observer readability.

Longer scale and larger number of scale graduations will result in more accurate observation.

The following terms related the various factors involved in observation:

Indicating travels: the length of the path covered by the indicating means or tip of the pointer in moving from one end of the scale to the other.

Resolution: the least interval between two adjacent discrete details, which can be distinguished one from the other.

Sensitivity: the ratio of a change in output magnitude to the change in input which causes it after the steady state has been reached.

ACCURACY RELATED TERM-STATIC: “how good are measurements under the steady state condition”??

Calibration: it is to ascertain output of a device corresponding to a series of values of the quantity the device is to measure, receive or transmit.

Date so obtained are used for:

a. Determination of location at which scale graduations are to be placed.

b. Adjustment of output, to bring it to the desired value, within a specified tolerance. And

c. Ascertaining the error by comparing the device output reading against a standard.

ii. Accuracy: it is a degree of conformity of an indicated value to a recognized accepted standard value or ideal value.

iii. Error: the algebraic difference between the indicated value and the true value of measured signal.

Error=indicate value- true value

+ve value means the indicated value is higher than the true value

Instrumentation system It is a physical system, which is a collection of physical objects

connected in such a way to give the desired output response.

Instrumentation systems can be classified into two main categories :

1. Analog system: deal with measurement information in an analog form.

analog signal may be defined as a continuation function, such as a plot of voltage against time or displacement against force.

2. Digital systems handle measurement information in digital form.

a digital quantity may consist of a number of discrete and discontinuous pulse whose time relationship contains information regarding magnitude or the nature of quantity.

The instrumentation system plays an important role in automation.

An automatic control system(or automation)requires a comparator(error detector)which measures the difference between the actual and the desired performance and actuates the control element

Elements of measurement system The operation of a measurement system can be explained in terms of

the functional elements of the system.

One can generalize a measurement system into such elements:

1. Primary Sensing Element: the physical quantity under measurement is called the measurand, makes its first contact with the primary sensing element of a measuring system.

It may have a non-electrical input and output (such as manometer), or an electrical input and output, such rectifier.

In the first case, it is converted into electrical signal by transducer.

Many a times certain operations are to be performed on the signal before its further transmission so that interfering sources are removed so that the signal may not get distorted.

The process called signal condition.

2. Variable Conversion Element: now the output may or may not suit to the system, it may be necessary to convert this output to some other suitable form while retaining the information content of the original signal.

Example: if the output is in analog form and the next stage of the system accepts the input only in digital form, then analog digital converter will be required.

3. Variable Manipulation Element: its function is to manipulate the signal presented to it while preserving the original nature of the signal.

Example: an electronic amplifier converts a small low voltage input signal to high voltage output signal ,this voltage amplifier acts as a variable manipulation element.

When the elements of an instruments are to be physically separated out, it becomes necessary to transmit data from one to another….data transmission element.

4. Data Presentation Element: the information regarding measured is to be conveyed to the personnel handling the instrument or the system for monitoring, controlling or analysis purpose.