Measurements are pretty important to engineers— how else do we get our data?. These measurements include data such as mass, velocity, pressure, strain, and temperature. When that data is some sort of “dimension”, we are talking about metrology. Engineers care about good dimensional measurements from two different directions.

The first direction is forward. In design, accurate measurements are essential to ensure that parts or processes under design are dimensioned correctly. Then after a part is finally manufactured, it must be inspected for quality to be sure that the final product matches the designer’s intentions.

The second direction is backward. The very first stage of design is understanding the problem at hand. This can take the form of such activities as reverse engineering (as we will study in a later lab), or simply basic scientific investigation into poorly understood phenomena (think, for example, of the difficulties associated with fatigue and wear) of relevance to a particular engineering problem. In such cases, accurate measurements of the unknown are the basic tool engineers have to assemble the facts from which scientific hypotheses can be deduced and then tested. Metrology is also a fine avenue for discussing accuracy, error, and calibration.

Objective:

In this lab students will be introduced to metrology and the basic concepts of accuracy, error, and calibration. They will also be given instruction in the use of basic metro-logical instruments.

Hitting the Mark: Accuracy and Error

You may have heard the expression “close enough for engineering.” It is a reference to accuracy— how good is the measurement (dimensional or otherwise)? More specifically, accuracy is a reference to the relative magnitude of the error in one or more measurements— how close is my measurement to the true value? Typically, one device (or technique, for that matter) is said to be more accurate than another because it gives measurements that have smaller errors.

List of Major Experiments:

1. Taking measurements using following instruments:

(i) Vernier height & depth gauge, (ii) Dial micrometer, (iii) Thread gauge, (iv) Radius gauge, (v) Filler gauge, (vi) Slip gauge.

2. Measurement of angle of a component using:

(i) Vernier bevel protractor, (ii) angle gauges, (iii) Sine-bar and slip gauges.

3. Checking / measuring parallelism, cylindricity and concentricity of components using dial indicator.
4. Measurement of a specific dimension for a lot of components, and prepare a histogram from the data obtained.
5. Measurement of surface finish by a Talysurf instrument.
6. Measurement of micro feature of a product (eg. Thread of a bolt or saw etc.) in a profile projector.
7. Determine natural cooling characteristics of a heated object by using a thermocouple.
8. Measurement of air velocity across an air duct using anemometer.
9. Fixing a strain gauge on a cantilevered flat section of steel. Then calibration of it as a force dynamometer using a Wheatstone bridge and loading arrangement.

Equipments:

VERNIER HEIGHT GAUGE
UNIVERSAL BEVEL PROTECTOR
RADIUS GAIGE
FEEDER GAUGE
THREAD GAUGE
SIN BAR
SLIP GAUGE
ANEMOMETER
THERMOCOUPLE
BLOWER WITH AIR DUCT
STRAIN GAUGE