Mechanical and Electromechanical Measurement Principles [US Army Subcourse MM 0486]

153 Pages·1986·3.665 MB·English

SUBCOURSE EDITION
MM0486 8

MECHANICAL AND
ELECTRO-MECHANICAL
MEASUREMENT PRINCIPLES
U.S. ARMY SIGNAL CENTER AND FORT GORDON
Fort Gordon, GA

E R R A T A S H E E T

SIGNAL SUBCOURSE SM0486
EDITION 8

MECHANICAL AND ELECTRO-MECHANICAL PRINCIPLES

Effective: 6 Jun 86

IMPORTANT READ AND POST

ADMINISTRATIVE INSTRUCTIONS:
Make the following changes:

1. Examination, page 151, question 13
Delete "You apply 300 psig to a gage and it indicates 312 psig."
Add "A gage has a range of 0 to 300 psig and actually indicates 312 psig when
you apply a true pressure of 300 psig."

PLEASE NOTE

Proponency for this subcourse has changed from Signal
Center & School (SM) to Ordnance Missile and Munitions
Center & School (MM).

IMPORTANT READ AND POST
SM0486

READ THIS PAGE

GENERAL INFORMATION

This subcourse consists of one or more lessons and an examination. Each of the
lessons is divided into two parts; the text and the lesson exercises. For one
lesson subcourse the lesson exercise serves as the examination. A heading at the
beginning of each lesson gives the title, the hours of credit, and the objectives
of the lesson. The final examination consists of questions covering the entire
subcourse.

If a change sheet is included, be sure to post the changes before starting the
subcourse.

THE TEXT

All the text material required for this subcourse is provided in the packet. The
text is the information you must study. Read this very carefully. You may keep
the text.

THE LESSON EXERCISES

Following the text of each lesson are the lesson exercises. After you hove studied
the text of each lesson, answer the lesson exercises. After you have answered all
the questions, go back to the text and check your answers. Remember your answers
should be based on what is in the text and not on your own experience or opinions.
If there is a conflict, use the text in answering the question.

When you are satisfied with your answers, check them against the approved solution
in back of this text. Re-study those areas where you have given an incorrect
answer by checking the reference given after each answer.

THE EXAMINATION

After you have completed all the lessons and exercises, select the correct answer
to all the examination questions. Carefully mark the correct answer on the exam
response sheet. Be sure to include your social security number, subcourse number,
and edition number are correct. Final exams should be mailed in the envelope
provided. The exam will be graded and you will be notified of the results. Your
final grade for the subcourse will be the same as your examination grade.

*** IMPORTANT NOTICE ***

THE PASSING SCORE FOR ALL ACCP MATERIAL IS NOW 70%.

PLEASE DISREGARD ALL REFERENCES TO THE 75% REQUIREMENT.

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ACKNOWLEDGEMENTS

This subcourse has been adapted from Air Force Career Development Course CDC
32470 for Army use.

Information and illustrations used to support the material in this subcourse
were adopted from manufacturer's instruction manuals published by the companies
listed below:

M. B. Electronics
Wm. Ainsworth and Sons, Inc.

SOLDIER'S TASK

This subcourse supports the following MOS 35H Tasks:

093-435-1270 Calibrate Torque Tester
093-435-1271 Calibrate Torque Wrench
093-435-1283 Calibrate Compound Gauge
093-435-1290 Calibrate Thermometer
093-435-3261 Calibrate Gram Weight Set
093-435-3300 Calibrate Thermometer Set

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CORRESPONDENCE COURSE
OF THE
U.S. ARMY SIGNAL CENTER & SCHOOL

AIPD Subcourse Number SM0486

Mechanical and Electro-Mechanical

Measurement Principles

(8 credit hours)

INTRODUCTION

Mechanical and electro-mechanical devices play an important role in our
everyday life. Lesson one of this subcourse includes information which will help
you understand molecular activity changes and the relationship of these changes to
heat. It also explains the operating principles for related heat sensing and
measuring instruments. The second lesson explains the physical principles of
pressure measurements and also includes information on pressure devices which you
must use and calibrate. Lesson three contains information on rotary and torque
measurements. It also includes information which will help you understand the
operating principle of the proving rug. Lesson four discusses the principle which
you must apply to perform vibration measurements and tells you when you must
calibrate vibration equipment. Lesson five teaches operation of the analytical
balance and principles of mass measurement. This subcourse is organized as
follows:

Lesson 1 Temperature and Humidity Measurements..............2 Hours
Lesson 2 Pressure Measurements and Devices..................2 Hours
Lesson 3 Rotary Torque Measurements and Equipment...........1 Hour
Lesson 4 Vibration Measurements and Equipment...............1 Hour
Lesson 5 Weights and Balance................................1 Hour
Examination.................................................1 Hour

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LESSON 1: TEMPERATURE AND HUMIDITY MEASUREMENT

AIPD Subcourse Number SM0486...........MECHANICAL AND ELECTRO-MECHANICAL
MEASUREMENT PRINCIPLES

Lesson Objective.......................Given learning objectives and text, you
should be able to answer all exercise
questions pertaining to the nature of heat
and temperature, temperature scales and
thermometers, heat sensing and measuring
instruments, and humidity with no errors.

Credit Hours...........................Two

TEXT

1. INTRODUCTION

Your next assignment may be the calibration of a temperature measuring
instrument or the use of a temperature measuring instrument for calibration
purposes. Your job will be much easier if you have a complete understanding of the
terms and principles associated with temperature measurements. The information
contained in this chapter concerns the nature of heat and temperature, the methods
by which heat is generated and transferred, the units used in temperature
measurements, and the principles applied in temperature measurements.

2. THE NATURE OF HEAT AND TEMPERATURE

a. Heat is considered to be a form of energy. The terms "thermal" and
"kinetic" are usually added as confusion factors. To make your day complete, some
authors use the terms "heat" and "temperature" as if they are the same. Let's see
if we can identify some of the terms associated with heat and temperature
measurements and establish practical definitions for these terms.

b. Heat. Most of us use the word "heat" without bothering to consider or
determine its true meaning. We usually have a general idea of what we mean when we
use the word, but for measurements in a laboratory, you must know precisely what
the word means and the conditions and limitations under which the meaning is true.
What answer would you give if a photographer, or an artist, or a common laborer
asked the question, "What is heat?" In your search for an answer, would you say
that heat:

Causes metals to expand?
Can be generated by rubbing two or more bodies together?
Is generated by compression?
Is an invisible weightless fluid called caloric?
Is electricity?

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Is a form of energy?

Is the total kinetic energy of moving molecules (a name applied to the kinetic
energy possessed by the moving molecules of a body)? Let's examine the list of
possible answers in sequence to see if any of them or a combination of them agrees
with your concepts of the nature of heat and what heat consists of.

(1) Heat and expansion. While the word "expansion" identifies one of the
effects heat produces in metals, it is not a satisfactory answer for the original
question of "What is heat?" We hope that you chose one or more of the other
answers. If you didn't, choose one before we proceed.

(2) Heat and friction. You know that the moving parts of the engine of
your car generate heat because of friction. In some instances, the intensity of
heat is such that the resulting expansion of metals prevents the movement of some
parts. Although the preceding statements are true, the original question has not
been answered; you have only chosen one method whereby heat is generated.

(3) Heat and compression. When a gas is compressed, the space between
individual molecules is decreased. The decrease in space between molecules results
in an increase in the activities of the molecules involved. The increase in the
activities of the molecules results in an increase in the kinetic energy of the gas
compressed. All of the statements concerning an increase in heat (kinetic energy)
by means of compression are true; but have we answered the original question on the
nature of heat? Partially, yes. We say partially because the use of the
expression "kinetic energy" in parentheses following heat indicates that heat is
kinetic energy.

(4) Heat is an invisible weightless fluid called caloric. At one time heat
was considered to be the caloric just described. With the development of the laws
of the conservation of energy, the idea that caloric (heat) could be increased or
decreased as a separate entity (a quantity existing independent of other
quantities) was disproved. The increase or decrease in the quantity of heat is
always accompanied by the transformation of one form of energy to another. Another
failure; we still haven't given a satisfactory answer to the original question.
This one isn't even partly true.

(5) Heat is electricity. If heat is electricity, then electricity is heat.
Well, technically no. You already know that electrons which constitute electrical
currents are forced through resistances by an EMF (electromotive force). The
movement of these electrical particles creates an increase in the activity (kinetic
energy) of the particles concerned and a subsequent increase in the quantity of
heat on the electrical conductor. This means that electricity can be used to
produce heat, but we can't say that they are the same.

(6) Heat as a form of energy. This statement is acceptable as a general
definition for heat, but it should be combined with the last state-

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ment in the list to give a better explanation of what heat is. Heat is a name
given to that form of energy which represents the total kinetic energy (force
created by molecular motion) possessed by the moving molecules of a body. There
are other definitions for heat, but this one contains the concept you need to fully
understand the nature of heat.

(7) Heat and Energy. You have already learned something of the statues of
matter and energy, the basic relationship of energy to heat, and how energy is
transformed from one type to another (such as electrical energy to heat energy).
Our primary concern in this section of the lesson is to increase this knowledge to
the extent that you can:

(a) Visualize, understand, and describe the molecular theory of matter.

(b) Understand the relationship between the molecular structure of
matter and kinetic energy.

(c) Understand the relationship between kinetic energy and heat.

(d) Associate the forms of energy and the transformation of energy with
heat.

(e) Apply your knowledge of the molecular structure of matter, the
relationship of molecular activity to kinetic energy, and the relationship of
kinetic energy and heat to the heat measurements you make.

c. The molecular theory of matter. Let's assume that all matter is composed
of tiny particles called molecules and the molecules are arranged in a lattice
structure, as shown in figure 1. The individual molecules attract or repel their
neighbors in accordance with the separation between molecules. Generally speaking,
when the separation is large, the force between molecules is small and is one of
attraction. The molecules of the material represented in figure 1 are located at
separations such that the forces of attraction and repulsion are equal to support
our discussion.

Figure 1. Molecular lattice structure.

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(1) The letters R and A shown in figure 1 represent the forces of repulsion
(R) and attraction (A) between the molecules. The line drawn through the middle of
the lines between molecules is used to show that the forces of repulsion and
attraction are equal to that distance. When a fixed lattice as shown (figure 1),
the forces between molecules nearly cancel each other so that there is very little
vibratory motion.

(2) The lattice structure shown in figure 1 is similar to the symmetry of
structure in crystals. If the molecules are pressed closer together, the force of
repulsion increases. If the molecules are forced farther apart, the force of
attraction increases. External forces exerted on the molecules of the lattice in a
solid cause the molecules to vibrate about their center positions. This vibration
motion is relatively weak, and the centers of the molecules remain fixed.

(3) In liquids the molecules are free to move greater distances. Since the
vibratory motion in liquids is greater than in solids, the energy which the moving
molecules can transfer to other molecules (kinetic energy) is greater. The
relationships between molecular separation forces, molecular kinetic energy, and
resulting-temperature conditions are shown in Table 1.

TABLE 1

THERMAL PROPERTIES OF SOLIDS, LIQUIDS, AND GASES

d. From the preceding paragraphs and Table 1, you should conclude that:

(1) Heat is the kinetic energy which a body possesses.
(2) Heat can be generated by means of electricity, compression, or
friction.
(3) Kinetic energy is the work potential which a body possesses because of
its motion.
(4) Normally, the forces of attraction between molecules in a solid are
strong, the molecular energy is small, and the temperature values are low.

e. Molecular kinetic-energy level changes. Let us restate our conclusions
from the preceding paragraphs in a simple statement. When we think of heat, we
should think of kinetic energy. Because molecular kinetic

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energy is the energy of molecules in motion, heat considerations must also include
the vibratory motion of molecules. Our primary point of concern is that heat
measurements are affected by the vibratory motion of molecules and the relative
changes in their motion. An increase in the heat that a body possesses is due to
an increase in its kinetic energy. In order to increase the molecular kinetic
energy in a body, you must increase the energy which produces the vibratory motion.

(1) The circuit in Figure 2 is an example of changing the kinetic energy
(molecular vibratory motion) level of components (resistors) in an electrical
circuit.

(2) From the circuit in Figure 2, you can see that the only factor,
affecting the power (kinetic energy) dissipated by the resistors are the voltage
(E) and the current (I). It is a simple series circuit in which the total current
flows through each resistor. Since the resistances are equal, the voltage drops
across the resistors are equal, and each resistor dissipates the same amount of
power. This means that the power values listed in figure 2 apply to R1 and R2.
The differences in power values listed in figure 2 represent the changes in applied
power (voltage and current) caused by changes in the power switch position. The
resulting changes in power values (kinetic energy) also represent changes in the
energy losses in the form of heat. Table 2 is included to help you understand how
changes in the values of power applied to a circuit (or body) produce changes in
the kinetic energy of that body.

Figure 2. Energy, heat, and power in an electrical circuit.

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