Methods engineeringTime study

Calculation of standard time or typical time

The calculation of standard time or typical time is the first stage in the data processing of time study. Although the specialist in the middle of the analysis may consider it necessary to observe the operations again, this stage does not require a great mastery of arithmetic. It consists of common and current calculations that can be done in a short time with the help of an assistant or using a spreadsheet. However, it does require a great capacity for consistency analysis of the data obtained in the observation phase and an evident knowledge of the measures to be taken depending on the situation present.

How to convert observed times to standard time?

Converting a series of observed times into standard or typical times requires the systematic application of a series of steps in which it is important that the analyst has clarity on the theoretical basis of work chronometry, the assessment of rhythm, and the supplements of the study.

1.
Analysis of data consistency

The analysis of the consistency of each element requires studying the variations that can be perceived in the observed times. The measures that must be taken according to the results of each analysis are as follows:

 

  • If it is determined that the variations are due to the nature of the element, all readings are preserved.
  • If it is determined that the variations are not caused by the nature of the element, and the previous and/or subsequent reading where the variation is observed are consistent; the inconsistency of the element will be due to the lack of skill or ignorance of the task on the part of the worker. In this case, if a large number of observations are consistent, it is possible to eliminate the extreme observations and only preserve the normal ones. In the same case, if it is not possible to distinguish between extreme and normal observations, the study must be repeated entirely with another worker.
  • If it is determined that the variations are not due to the nature of the element, but the reading before and/or after the element where the variation is observed has also suffered variations; this situation occurs due to errors in the chronometry, committed by the timekeeper. If the number of extreme cases is minimal, these are eliminated, and only the normal ones are preserved. If, on the other hand, this error has been committed in many readings, even if not all of them are in the same element; the most appropriate thing is to repeat the study, and this repetition must be done as many times as necessary until an appropriate consistency is achieved in the observations of each element.
  • If it is determined that the variations have no apparent cause, they must be carefully analyzed before being eliminated (if it is possible to return to the observation phase). An abnormal reading should never be accepted as inexplicable. In case of doubts, it is recommended to repeat the study.

To avoid repeating the study, it is recommended to recognize the importance of special notes in the chronometry process, as this information is vital to identify the causes of a given variation.

It is crucial that the professional takes into account from this stage that the process in question can be affected by variability, so standard time applications must take into account this underlying phenomenon.

2. Calculation of the average per element

After the data consistency analysis phase, we move on to a simple arithmetic stage. We must calculate an average for each element of the operation that has been observed at different times. To obtain the average per element, it is necessary to:

  • Add the readings that have been considered consistent.
Element 1 readings
1 2 3 4 5 6 7 8 9 10 Suma (ΣXi)
0.345 0.335 0.350 0.347 0.501 0.345 0.350 0.349 0.344 0.345 3.11

In this case, reading No. 5 is not considered consistent (phase 1).

 

  • The number of readings considered consistent for each element is noted (CR = Consistent Readings).
1 2 3 4 5 6 7 8 9 10 Suma (ΣXi) LC
0.345 0.335 0.350 0.347 0.501 0.345 0.350 0.349 0.344 0.345 3.11 9

In this case, the number of consistent readings is equal to 9.

 

  • For each element, the sums of the readings are divided by the number of readings considered; the result is the average time per element (Te = Average Time per Element).

    \[Te = \frac{\sum Xi}{CR}\ \ for\ example \ Te = \frac{3.11}{9} = 0.345\]

3. Convert observed times to normal basic times

For the development of this phase, it is necessary to consider the nature of the assessment of the work rate, that is, through which method the rhythm with which the observed activities were developed was determined, whether a factor was determined for each element or for each observation.

  • If an evaluation has been determined for each element, the following procedure will be applied to each element (Tn = Normal Time):

    \[Tn= Te\ \times \ \frac{Assigned\ value}{Standard\ value}\]

For example, if we assume that the worker had a work rate factor of 95 (which indicates that they worked below the expected cadence); and we assume, as is common, that the standard pace factor is equal to 100; we will have that, for an average time of 0.345:
  • If an evaluation has been determined for each reading (time observation), the following procedure will be applied to each element:

    \[Tn= Te\ \times \ \frac{\sum Assigned\ values}{Standard\ values\ \times CR}\]

If the average of the element has already been calculated, the first method should be used. Otherwise, and with the help of a spreadsheet, it is more convenient to convert the observed times to basic or normal times for each reading and then calculate the average of these. In this way, the same result will be obtained.

4. Addition of supplements (granted time per element)

In this step, the standard or normal time is added to the tolerances for granted supplements, obtaining the granted time for each element. It is common for supplements to be determined in terms of percentages, so these factors must affect the time of each element, as long as the conditions that were evaluated to determine the supplements are part of the operational context in which each observed activity was carried out.

The following procedure will be applied to each element (Tt = Elemental Conceded Time):


    \[Tt= Tn\ + \left ( 1\ +\ supplements \right )\]

For example, if we assume that the element has supplements of 13%, we will have (for a normal time of 0.328):


    \[Tt= 0.328\ + \left ( 1\ +\ 0.13 \right ) \simeq 0.371\]

5. Smoothing by frequency (total granted time)

In this step, the frequency per operation or piece of each element is calculated, that is, how many times is the element executed to produce a piece? Repetitive elements, by definition, occur at least once in each operation cycle, so in their respective row 1/1 will be placed if they occur once per operation, or 2/1 if they occur 2 times per operation.

Casual elements (for example, sharpening tools) usually only happen every 5, 10 or 50 cycles; in this case, the frequency row would be noted as 1/5 in the case of that element (sharpening tools, for example) occurring once every 5 operations, or 1/10 if it occurs once after 10 operations.

Then the Elemental Conceded Time (Te) is multiplied by the frequency of the element (which will be written, as already mentioned, as a fraction). The product of this multiplication will be called Total Conceded Time (TCt = Total Conceded Time).


    \[ TCt= Tt\ \times frequency\]

Let’s say that the element we have used as an example is a repetitive element and that it appears 3 times per operation. That is, in the operation to produce piece A, the element we will calculate must be performed 3 times (with a Tt time equivalent to 0.371):

    \[TCt= 0.371\ \times\ \frac{3}{1}= 1.113\]

6. Standard or type time

In this step, the total granted times for each element that is part of an operation are added, and the standard time per operation is obtained.


    \[\sum TCt = Standard\ Time\]

Let’s suppose that the element we have used as an example, called element “A”, is part of a series of elements called elements A, B, C, D, E, F. We will have the following:

Element TCt (Total Conceded Time)
A 1.113
B 2.106
C 1.590
D 3.520
E 1.008
F 1.464
Standard time (Σ(TCt)) 10.345

7. Additional considerations

Standard or type time is the total time it takes to perform a task at the standard pace.

When calculating standard time, the following should be considered:

  • How will contingent elements be assigned? Should they be apportioned or not?
  • If preparation and withdrawal time should be granted.
  • The interference factor when it is present in a studied work cycle.
  • How will variability affect the operation within a normal operational context?

Bryan Salazar López

By profession, Industrial Engineer, Master in Logistics, specialized in productivity, with interest and experience in modeling processes under sustainability indicators. Founder of Ingenieriaindustrialonline.com, site where research contributions, articles and references are collected.

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