Production
Operations management
Chapter 14
Work Study/
Method study
Work Study- Method study
Importance
™Managing people within operations involves actual design
decisions about jobs, methods, relationships between jobs
and machines and systems of control and communication.
™ Work design involves complex "people" relationships
between operative staff, supervisors and specialists e.g.
engineering managers and staff who commission new
machines and maintain them. Other specialists may coordinate health and safety systems or monitor performance
and plan maintenance
™People are not mere extensions to machines or
horsepower to be switched on and off. A worker's
performance may be better than a machine's capability - yet
a machine may outstrip the human being for many tasks.
Work Study
Definition
™People can be hurt/injured physically by operating
environments or trapped socially and psychologically in
them/by them. How operational systems are designed and
the jobs and performance relationships within them are of
great operational, economic and social importance. In this
context then work study is :
™A collection of techniques used to examine work what is done and how it is done - so that there is
systematic analysis of all the elements, factors, resources
and relationships affecting the efficiency and
effectiveness of the work being studied.
Work Study-Objectives
™Considerable diplomacy and sensitivity is needed by the
industrial engineer or operations manager who becomes
involved in work study (or business process improvement)
investigations.
™Method study and work measurement are two principal
activities of work study which originated in the work of F.
W. Taylor . FW's "scientific management" imperatives are:
winvestigate the work situation and identify weaknesses where and why is poor performance happening? The
"scientific" title for this approach to management means
placing emphasis on
wdata gathering and rational analysis
Work Study- Objectives
wcertain narrow assumptions about the objectivity of
efficiency criteria
wthe existence of direct, deterministic relationships
between worker performance and incentive payments and
wconsideration of the worker to some extent as a machine.
Thus we can evaluate and introduce improvements in
operating methods. This includes type of equipment, its use,
layout of operations, supply and use of materials, materials
handling, work organization, effectiveness of planning
procedures and so on.
Work Study- Benefits
Using data on measured work, unmeasured work and idle
time we can attempt to derive effectiveness indices.
Constable and New exemplify efficiency and effectiveness
indices
a.efficiency while performing measured work (ratio of
standard/measured hours of work produced and the actual
time taken)
b.effectiveness which includes
waccounting for work done for which no measured time
exists. Such work is typically paid for by an agreed
hourly/day rate i.e. there is no direct, measured relationship
between pay and how much work is actually completed in
that hour.
Work Study- Benefits
wOf course a supervisor may pass a judgment or state that
the amount of work and its quality are inadequate.
wrecognition of possible idle time caused e.g. by
management not allocating any work, supplier/materials
delays, machine breakdowns etc.
wImproved work flow
wBasis of sound incentive scheme
w Provides better job satisfaction.
wFare wages to employees
wReduced manufacturing cost
Time & Motion study
™A time and motion study would be used to reduce the
number of motions in performing a task in order to increase
productivity. The best known experiment involved
bricklaying.
™Through carefully scrutinising a bricklayer's job, Frank
Gilbreth reduced the number of motions in laying a brick
from 18 to about 5. Hence the bricklayer both increased
productivity and decreased fatigue.
™The Gilbreths developed what they called therbligs
("therblig" being "Gilbreth" spelled backwards, with a
slight variation), a classification scheme comprising 17
basic hand motions.
Relationship of Time &
Motion study to work study
™Both time & motion study which resulted from the
integration of concepts and practices developed by F,W
Taylor.
™However time study is quantitative analysis leading to
establishing time standards ,Whereas motion study is
Qualitative analysis leading to establishment of time
standards.
Work study as a discipline is concerned with :
™Better ways of performing tasks
™Exercising control over the output in respect of those jobs
by setting standards for performance
Relationship of Time &
Motion study to work study
™Motion Study is designed to determine to best way to
complete a repetitive job
™Time Study measures how long it takes an average worker
to complete a task at a normal pace
™Motion and time study helps management determine how
much is produced by workers in a specific period of time,
therefore making it easier to predict work schedules and
output.
™Motion and Time Study is a scientific method designed by
two different people for the same purpose, to increase
productivity and reduce unit cost.
™ The two methods evaluate work and try to find ways to
improve processes.
Relationship of Time &
Motion study to work study
™Motion Study
™Improve methods
™It measures distance, or how much you move to do a job,
and how much you get done in a period of time
™Time study
™Establish standards
™Looked at the average time it took an average worker
™Users of Time Study have to establish standards, this
works in the service industry,
Relationship of Time &
Motion study to work study
Work Study
Method Study
Motion Study
Work
Measurement
Time Study
Work Study- Method study
Methods study
- is an analysis of ways of doing work. The memonic
SREDIM (a common-sense heuristic or general
problem-solving strategy) represents the method study
stages
1. select the tasks to study
2. record the facts about it
3. examine these
4. develop a new method
5. install/implement it
6. maintain it
Work Measurement
Definition
™ Work Measurement is a term which covers several
different ways of finding out how long a job or part of a job
should take to complete. It can be defined as the systematic
determination, through the use of various techniques, of the
amount of effective physical and mental work in terms of
work units in a specified task. The work units usually are
given in standard minutes or standard hours.
™Why should we need to know how long a job should
take? The answer to this question lies in the importance of
time in our everyday life. We need to know how long it
should take to walk to the train station in the morning, one
needs to schedule the day's work and even when to take out
the dinner from the oven.
Work Measurement
Definition
™ In the business world these standard times are needed
for:
™planning the work of a workforce,
™manning jobs, to decide how many workers it would need
to complete certain jobs,
™scheduling the tasks allocated to people
™costing the work for estimating contract prices and
costing the labor content in general
™calculating the efficiency or productivity of workers - and
from this:
™providing fair returns on possible incentive bonus
payment schemes.
Work Measurement
Techniques
™ On what are these standard times set? They are set, not
on how long a certain individual would take to complete a
task but on how long a trained, experienced worker would
take to do the task at a defined level of pace or performance.
™Who sets these standard times? Specially trained and
qualified observers set these times, using the most
appropriate methods or techniques for the purpose i.e.
"horses for courses".
™How it is done depends on circumstances that obtain. The
toolkit available to the comprehensively trained observer is
described below.
Work Measurement
Techniques
™ Selecting the most appropriate methods of work
measurement
™The method chosen for each individual situation to be
measured depends on several factors which include:
™the length on the job to be measured in time units
™the precision which is appropriate for the type of work in
terms of time units (i.e. should it be in minutes, hundredths
or thousandths of a minute)
™the general cycle-time of the work, i.e. does it take
seconds, minutes or days to complete
Work Measurement
Techniques
™ The length of time necessary for the completion of the
range of jobs can vary from a few seconds in highly repetitive
factory work to several weeks or months for large projects
such as major shutdown maintenance work on an oil refinery.
™It is quite clear that using a stop-watch, for example, on the
latter work would take several man-years to time to measure!
Thus, more "overall" large-scale methods of timing must be
employed.
™The precision is an important factor, too. This can vary
from setting times of the order of "to the nearest thousandth
of a minute" (e.g. short cycle factory work) to the other end of
the scale of "to the nearest week"
Work Measurement
Techniques
™ These are the dominant factors that affect the choice of
method of measurement.
™The methods
™PMTS.
™At the "precision" end of the scale is a group of methods
known as predetermined motion time systems that use
measurement units in ten thousandths (0.0001) of a minute
or hundred-thousandths of an hour (0.00001 hour).
™The resulting standard times can be used directly, for very
short-cycle work of around one minute total duration such
as small assembly work.
Work Measurement
Techniques
™ However, they often are used to generate regularly used
basic tasks such using assembling or disassembling nuts and
bolts, using a screwdriver and similar. Tasks of this type are
filed as standard or synthetic data-banks.
™Estimating.
™At the other end of the scale (long-cycle and project work)
we need something which is quick to use. Such a method is
estimating. This can exist in three main forms.
™Analytical estimating relies on the experience and judgment
of the estimator. It is just of case of weighing up the work
content and, using this experience, stating a probable time for
completion, such as "this job will take about eight days to
complete".
Work Measurement
Techniques
™ Category estimating. This is a form of range estimating
and requires a knowledge of the work.
™Estimators may not feel comfortable with overall,
analytical estimates upon which may depend the outlay of a
great deal of money.
™They often prefer giving a range estimate such as "this job
should take between 12 weeks and 14 weeks to complete",
which provides a safety net should things go wrong. Such
ranges are not just picked upon at random but are statistically
calculated and based on probability theory.
™Comparative estimating. This is another example of range
estimating. Again, estimators rely on experience of the work
in order to produce estimates.
Work Measurement
Techniques
™ This experience can be augmented by the provision of
each time-range with a few typical, descriptive, jobs that
would guide estimators to the most appropriate range. The
estimator would compare the work to be estimated with
those in the various ranges until the most appropriate fit is
found.
™Timing.
™The intermediate method between the two groups above,
is timing the work in some way, usually with a stop-watch
or computerized electronic study board. This method is
retrospective in that the job must be seen in action in order
to be timed whereas the other methods are prospective and
can be used for timing jobs before they start.
Work Measurement
Techniques
™ The observer times each element of the work and obtains
times that the observed operator takes to do the elements.
Each timing is adjusted (rated) by the pace at which the
operator was working as assessed by the observer. This
produces basic times for the elements and hence the whole
job, which are independent of the operator and can be used
as the time for a trained, experienced worker to carry out the
same elements..
™Another method of assessing the work is using activity
sampling and rated activity sampling. This is a method
based on the observer making snap observations at random
or systematic sample times,
Work Measurement
Techniques
™ observing what the operator is (or operators are) doing at
the times of those observations
™Models:
™A most useful method for standard or synthetic databanks of job or element times is using computer models of
the jobs. These are generated as mathematical formulae in
which the observed data are inserted to compile a time for
completion of the task or project. It is a useful method for
recycling time standards for elements of basic work over
and over again, only changing the values of the variables to
suit each project
Steps in Work Measurement
Involves assessing the time a job should take to do. Similar
steps are involved as to method study
1. Select the tasks
2. Break the job into elements
3. Record the facts,record time taken
4. Analyze them
5. Assess relaxation allowance
6. Calculate basic and standard times for the task
7. Agree the method and its related time
Work Measurement
Time study
Time study is a structured process of directly observing and
measuring (using a timing device) human work in order
to establish the time required for completion of the work
by a qualified worker when working at a defined level
of performance.
It follows the basic procedure of systematic work
measurement of :
™ analysis (of the work into small, easily-measurable
components or elements);
™ measurement (of those components); and
™ synthesis (from those measured components to arrive at
a time for the complete job).
Work Measurement
Time study
™ The observer first undertakes preliminary observation of
the work (a pilot study) to identify suitable elements which
can be clearly recognized on subsequent occasions and are
convenient, in terms of their length, for measurement.
™Subsequent studies are taken during which the observer
times each occurrence of each element (using a stopwatch
or other timing device) while at the same time making an
assessment of the worker's rate of working on an agreed
rating scale. (One of the prime reasons for measuring
elements of work, rather than the work as a whole is to
facilitate the process of rating.
Work Measurement
Time study
™ The rate at which a worker works will vary over time; if
elements are carefully selected, the rate of working should
be consistent for the relatively short duration of the element.
More information on rating is given within the entry on
work measurement.)
™This assessment of rating is used to convert the observed
time for the element into a basic time - a process referred to
as "extension". It is essential that a time study observer has
been properly trained in the technique and especially in
rating.
™Time study, when properly undertaken, involves the use
of specific control mechanisms to ensure that timing errors
are within acceptable limits.
Work Measurement
Time study
™ Increasingly, timing is by electronic devices rather than
by mechanical stopwatch; some of these devices also assist
in subsequent stages of the study by carrying out the
process of "extending" or converting observed times into
basic times.
™The number of cycles that should be observed depends on
the variability in the work and the level of accuracy
required. Since time study is essentially a sampling
technique in which the value of the time required for the job
is based on the observed times for a sample of observations,
it is possible using statistical techniques to estimate the
number of observations required under specific conditions.
Work Measurement
Time study
™ This total number of observations should be taken over a
range of conditions (where these are variable) and, where
possible, on a range of workers.
™Once a basic time for each element has been determined,
allowances are added (for example, to allow the worker to
recovered from the physical and mental effects of carrying
out the work) to derive a standard time.
™Time study is a very flexible technique, suitable for a
wide range of work performed under a wide range of
conditions, although it is difficult to time jobs with very
short cycle times (of a few seconds).
Work Measurement
Time study
™ Because it is a direct observation technique, it takes
account of specific and special conditions but it does rely on
the use of the subjective process of rating.
™However, if properly carried out it produces consistent
results and it is widely used.
™ Additionally, the use of electronic data capture devices
and personal computers for analysis makes it much more
cost effective than previously.
Work Measurement
Time study
™ There are various ways in which work may be measured
and a variety of techniques have been established. The basic
procedure, irrespective of the particular measurement
technique being used, consists of three stages ;
wan analysis phase in which the job is divided into
convenient, discrete components, commonly known as
elements;
wa measurement phase in which the specific measurement
technique is used to establish the time required (by a
qualified worker working at a defined level of performance)
to complete each element of work;
Work Measurement
Synthesis
™ A synthesis phase in which the various elemental times
are added, together with appropriate allowances (see below),
to construct the standard time for the complete job.
wThe techniques used to measure work can be classified
into those that rely on direct observation of the work, and
those that do not.
wFor example, some techniques, such as predetermined
motion-time systems and the use of synthetic or standard
data can provide times from simulation or even visualization
of the work. However, the data on which such techniques
are based were almost certainly based on earlier observation
of actual work.
Work Measurement
Synthesis
™ Rating
™Direct observation techniques (such as time study and
analytical estimating) include a process for converting
observed times to times for the "qualified worker working at
a defined level of performance." The commonest of these
processes is known as rating.
™This involves the observer (after appropriate training)
making an assessment of the worker's rate of working
relative to the observer's concept of the rate corresponding to
standard rating. This assessment is based on the factors
involved in the work - such as effort, dexterity, speed of
movement, and consistency.
Work Measurement
Synthesis
™ The assessment is made on a rating scale, of which there
are three or four in common usage. Thus on the 0-100 scale,
the observer makes a judgment of the worker's rate of
working as a percentage of the standard rate of working
(100).
™The rating is then used (in a process known as "extension"
in time study) to convert the observed time to the basic time
using the simple formula:
™
™Basic time = observed time x observed rating/standard
rating
Work Measurement
Synthesis
™ Rating is regarded by many as a controversial area of
measurement since it is a subjective assessment. Where
different observers rate differently, the resulting basic times
are not comparable.
™However, practiced rating practitioners are remarkably
consistent. It is important that those undertaking the rating
are properly trained, and that this training is regularly
updated (to maintain a common perception of standard
rating) through rating 'clinics'.
™Allowances
™When carrying out work over a complete shift or working
day, workers obviously suffer from the fatigue imposed both
by the work undertaken
Work Measurement
Synthesis
™ and the conditions under which they are working. The
normal practice is to make an addition to the basic time
(commonly referred to as an "allowance") to allow the
worker to recover from this fatigue and to attend to personal
needs.
™ The amount of the allowance depends on the nature of the
work and the working environment, and is often assessed
using an agreed set of guidelines and scales.
™It is usual to allow some of the recovery period inherent in
these allowances to be taken away from the workplace (and
it is essential in adverse working conditions). Thus, work
design should include the design of an effective work-rest
regime..
Work Measurement
Synthesis
™ The addition of allowances should never be used to
compensate for an unsafe or unhealthy working
environment.
™One minority school of thought suggests that relaxation
allowances are unnecessary. With work which involves, say,
the carrying of heavy weights, this school suggests that the
observer automatically adjusts the concept of standard rating
to allow for the weight.
™Thus, if the standard rate of performance for walking on
level ground carrying no weight is equivalent to four miles
per hour, then an observer rating a worker walking while
carrying a weight will not expect the equivalent rate.
Work Measurement
Synthesis
™ Thus, it is argued that the weight has been allowed for in
the adjustment of standard rating and any relaxation
allowance is simply a duplication of this adjustment.
™In many jobs there are small amounts of work that may
occur irregularly and inconsistently.
™It is often not economic to measure such infrequent work
and an additional allowance is added to cover such work and
similar irregular delays.
™This allowance is known as a contingency allowance and
is assessed either by observation, by analysis of historical
records (for such items as tool sharpening or replacement),
or by experience.
Work Measurement
Synthesis
™ The end result is a standard time which includes the time
the work "should" take (when carried out by a qualified
worker) plus additional allocations in the form of
allowances, where appropriate, to cover relaxation time,
contingency time and, perhaps, unoccupied time which
increases the overall work cycle (such as waiting for a
machine to finish a processing cycle).
™Choosing a measurement technique
™The choice of a suitable measurement technique depends
on a number of factors including:
wthe purpose of the measurement;
wthe level of detail required;
Work Measurement
Synthesis
™ the time available for the measurement;
wthe existence of available predetermined data;
wand the cost of measurement.
™To some extent there is a trade off between some of these
factors. For example, techniques which derive times quickly
may provide less detail and be less suitable for some
purposes, such as the establishment of individual
performance levels on short-cycle work.
™The advantage of structured and systematic work
measurement is that it gives a common currency for the
evaluation and comparison of all types of work.
Work Measurement
Synthesis
™The results obtained from work measurement are
commonly used as the basis of the planning and scheduling
of work, manpower planning, work balancing in team
working, costing, labor performance measurement, and
financial incentives.
™ They are less commonly used as the basis of product
design, methods comparison, work sequencing, and
workplace design
Work Measurement
Synthesis
™The results obtained from work measurement are
commonly used as the basis of the planning and scheduling
of work, manpower planning, work balancing in team
working, costing, labor performance measurement, and
financial incentives.
™ They are less commonly used as the basis of product
design, methods comparison, work sequencing, and
workplace design
Work Measurement
Analytical Estimating
™Analytical estimating would normally be used for
assessing work over a reasonably lengthy period of time,
where it may be difficult and more expensive to collect the
information required using other measurement techniques.
™ Also, in some work environments the presence of an
individual carrying out work measurement in the work place
could be unacceptable.
™In these cases, analytical estimating may be an appropriate
method to use, assuming someone with experience of the
work is available to apply their experienced judgment. ( This
may be work measurement personnel who have previous
experience of this particular work )
Work Measurement
Analytical Estimating
™However, the work content of some jobs cannot be
estimated in advance because one is unclear about what is
required until an assembly operation has been tested or
stripped down. For example, during the progress of repair
unforeseen and non standard difficulties can arise.
Removing a wooden door from its frame by unscrewing 8 or
12 screws could take five minutes if the screws were
recently inserted, or a great deal longer if the screws are
rusted and clogged with paint.
™In summary, the technique is used most commonly in any
work environment where a lengthy time (and associated
high cost) is needed to collect data.
Work Measurement
Analytical Estimating
™This technique of work measurement is used to determine
the time values for job having long and non repetitive
operations
Procedure for Analytical estimating
™Find out job details
™Break the job into elements
™Select time values from standard data for as many
elements as possible.
™Estimate time value remaining elements from past
experience
™Add above time values to get total basic or normal time
™Add relaxation allowance
Work Measurement
Analytical Estimating
Advantage
Perhaps the most significant advantage of using analytical
estimating is its speed of application and low cost. Using
trained and experienced personnel process and measurement
data can be quickly assembled and applied.
™Helps in planning
™Reliable
™Economical
™Used for estimating labor times for preparing cost
estimates
™Steps to improve labor control
Work Measurement
Analytical Estimating
Disadvantage
™However, the use of experienced judgment when
determining the time necessary to perform a task is the
technique's most obvious source of weakness when
compared with a more precise technique such as time study.
™ This is why the technique would not normally be used
when a more precise and accurate alternative is a feasible
and economic alternative, particularly to highly repetitive,
standardized operations.
™ Many jobs, such as craft work in the maintenance field,
consist of a group of tasks which are periodically repeated
but the precise nature of each task varies each time in minor
respects
Work Measurement
Predetermined motion time system (PMTS)
™Definition:
™PMT Systems are methods of setting basic times for doing
basic human activities necessary for carrying out a job or
task.
™The definition in BS 3138, Glossary of Terms Used in
Work Study is: 'Tables of time data at defined rates of
working for classified human movements and mental
activities. Times for an operation or task are derived using
precise conventions. Predetermined motion time data have
also been developed for common combinations of basic
human movements and mental activities'.
Work Measurement
Predetermined motion time system (PMTS)
™The concept of PMTS is to analyze a job into its
fundamental human activities, apply basic times for these
from tables and synthesize them into a basic time for the
complete job. The basic elements include the following:
™reach for an object or a location,
™grasp an object , touching it or closing the fingers around
it,
™move an object a specified distance to a specified place,
™rewraps an object in order to locate it in a particular way,
usually prior to:
™release an object to relinquish control on it,
™other elements for assembling to, or inserting an object
into, its intended location.
Work Measurement
Predetermined motion time system (PMTS)
™For each of these actions basic times are tabled. For
example, in Work-Factor the time unit is one thousandth of
a minute (the Work-Factor Time Unit) whereas in MTM the
unit is one hundred-thousandth of an hour (time
measurement unit, tmu).
™The times for basic actions are adjusted for other factors
which take into account such variables as:
™distances moved, in inches or centimeters
™difficulty in performing the actions, such as avoiding
obstacles during moves, closeness of fit during assembling,
weight of the object, all of which increase the times to carry
out the basic actions.
Work Measurement
Predetermined motion time system (PMTS)
™The above basic motions cover most of the actions
performed by humans when carrying out work. Other basic
activities include:
™walking to a specified place
™bending down and stooping
™kneeling on one knee and kneeling on both knees
™foot and leg motions
™sitting down and standing.
™Mental activities include times for: See, Inspect, Identify,
Nerve Conduct, React, Eye focus, Eye travel times,
Memorize, Recall, Compute (calculate) and others, mostly
from Work-Factor.
Work Measurement
Predetermined motion time system (PMTS)
™Levels of detail in systems
™In order to speed up measurement time the major systems
all include different levels of detail, such as:
1.most detailed systems: MTM and Detailed Work-Factor
2.Second level systems: MTM-2 and Ready Work-Factor
(abridged versions) achieved usually by the four methods of
combining, statistically averaging, substituting and/or
eliminating certain basic motions.
3.Third level systems: MTM-3 and Abbreviated WorkFactor (even more abridged)
4."higher level" systems, usually times for complete
activities.
Work Measurement
Predetermined motion time system (PMTS)
™A predetermined motion time system (PMTS) is
frequently used to set labor rates in industry by quantifying
the amount of time required to perform specific tasks. The
first such system is known as Methods Time Measurement,
released in 1948 and today existing in three variations,
commonly known as MTM-1, MTM-2, and MTM-3.
™ Another popular PMTS is the Maynard Operation
Sequence Technique, which was first released in 1972. That
method also has several variations, with the most commonly
used being BasicMOST, and others being MiniMOST,
MaxiMOST, and AdminMOST.
Work Measurement
Predetermined motion time system (PMTS)
™The variations of both systems differ from each other
based on their level of focus. MTM-1 and MiniMOST are
optimal for short processes with only small hand motions,
while MTM-3 and MaxiMOST are more properly used for
longer processes that are less repetitive.
™Unlike time studies, in which an analyst uses a stopwatch
and subjectively rates the operator's effort to calculate a
standard time, a PMTS requires that the analyst break apart
the process into its component actions, assign time values to
each action, and sum the times to calculate the total standard
time.
Work Measurement
Predetermined motion time system (PMTS)
™Most predetermined motion time systems use time
measurement units (TMU) instead of seconds for measuring
time. One TMU is defined to be 0.00001 hours, or
0.036 seconds.
™These smaller units allow for more accurate calculations
without the use of decimals. In the most in-depth PMT
systems, motions observed will be on the level of individual
TMUs, like toss (3 TMUs in MiniMOST) and simple pickup (2 TMUs in MTM-1).
™More general systems simplify things by grouping
individual elements, and thus have larger time values – for
example, a bend and arise (61 TMUs in MTM-2) and one or
two steps (30 TMUs in BasicMOST).
Work Measurement
Predetermined motion time system (PMTS)
™Systems with even less detail work with TMU values in
the hundreds, like climbing 10 rungs on a ladder (300 TMUs
in MaxiMOST) or passing through a door (100 TMUs in
MaxiMOST).
™The choice of which variation of a certain PMTS to use is
dependent on the need for accuracy in contrast to the need
for quick analysis, as well as the length of the operation, the
distances involved in the operation, and the repetitiveness of
the operation. Longer operations often take place on a larger
spatial scale, and tend to be less repetitive, so these issues
are often treated as one.
Work Measurement
Predetermined motion time system (PMTS)
™For longer, less repetitive operations, statistical analysis
demonstrates that the accuracy of less detailed systems will
generally approach the accuracy of more detailed systems.
™ Thus, in order to reduce the time required for analysis,
less detailed systems (like MTM-3 and MaxiMOST) are
usually used when possible.
™Conversely, very short, repetitive processes are commonly
analyzed with more exact methods like MTM-1 and
MiniMOST because of the need for accuracy.
Work Measurement
Predetermined motion time system (PMTS)
Applications of MTM techniques
MTM has been used for:
™Developing effective methods in advance of beginning the
production
™Improving existing method
™Estimating standard time
™Estimating labor time
™Training supervisors
™Choosing between alternative material
Work Measurement
Activity Sampling
Activity Sampling is a statistical technique that can be used
as a means for collecting data. It is defined by BS
3138:41008 as:
A technique in which a large number of observations are
made over a period of time of one group of machines,
processes or workers. Each observation records what is
happening at that instant and the percentage of observations
recorded for a particular activity or delay is a measure of the
percentage of time during which that activity or delay
occurs.
Work Measurement
Activity Sampling
™It is normally used for collecting information on the
percentages of time spent on activities, without the need to
devote the time that would otherwise be required for any
continuous observation.
™One of the great advantages of this technique is that it
enables lengthy activities or groups of activities to be
studied economically and in a way that produces statistically
accurate data.
™Fixed and Random Interval Sampling
™Activity Sampling can be carried out at random intervals
or fixed intervals. Random activity sampling is where the
intervals between observations are selected at random e.g.
from a table of random numbers.
Work Measurement
Activity Sampling
™Fixed interval activity sampling is where the same interval
exists between observations. A decision will need to be
made on which of these two approaches is to be chosen.
™A fixed interval is usually chosen where activities are
performed by a person or group of people who have a degree
of control over what they do and when they do it.
™Random intervals will normally be used where there are a
series of automated tasks or activities as part of a process,
that are have to be performed in a pre established regular
pattern.
™If fixed interval sampling were to be used in this situation
there is a danger that the sampling point would continue to
occur at the same point in the activity cycle.
Work Measurement
Activity Sampling
Confidence Levels
Remember, that activity sampling is used for assessing the
percentage of time spent on activities.
Because activity sampling conforms to the binomial
distribution it is possible to use a calculation to determine
how many observations will be needed to operate within
specified limits of accuracy.
The formula for the number of observations is as follows:
= 4 x p x (100 - p)
L2
Where p is the estimated % time spent on the activity
Where L is the limit of error, expressed as a %
Work Measurement
Activity Sampling
Once the above calculation has been completed the
observations can begin and activities are recorded at the
agreed time intervals. When they have been completed a
further calculation can be used to determine the error rate, as
follows:
Error Rate = ± 2 x √( p x (100 - p) )
Number of observations
This is very much an overview to the topic of activity
sampling, with a definition of what it is, its advantage over
continuous observation and the formulae that can be used to
establish the confidence levels that can be obtained.
Plant Location
End Of
Chapter 14