NAME : THANDEKA NCUBE

STUDENT NUMBER : N0183156F

FACULTY : INDUSTRIAL TECHNOLOGY AND

MANUFACTURING ENGINEERING

PROGRAMME : CHEMICAL ENGINEERING

COURSE CODE : TCE2109

COURSE NAME : CHEMICAL ENGINEERING LABORATORY

ENGINEERING INSTRUCTOR : L TSHUMA

LAB 5 : CALIBRATION OF AN ELECTRICAL BALANCE

1|Page
TABLE OF CONTENTS

Abstract………………………………………………………………………………….3

Introduction……………………………………………………………………………..4

Experimental…………………………………………………………………………….5

Results Analysis………………………………………………………………………….6 - 7

Conclusions………………………………………………………………………………8

Appendix….………………………………………………………………………………9-10

References………………………………………………………………………………..11

2|Page
ABSTRACT

Calibration refers to the comparison between know measurements and the measurements
using your instrument. It aims at checking the accuracy of the instrument and at determining
the traceability of the measurements. The accuracy of instruments degrades overtime due to
normal wear and tear, electric or mechanical shock or a hazardous environment depending on
the instrument and the environment in which it is being used. Measuring instruments should
therefore be calibrated as per manufacturer’s recommendation, after electric shock and
periodically, be it monthly, annually or quarterly. In this experiment, an analytic balance was
calibrated. Analytic balances are a very sensitive piece of equipment and can measure a mass
down to 0.00001 grams. When calibrating an analytic balance one has to wipe of dust or
particles that might interfere with the measurement process. The balance was tare to a reading
of zero and weighed weights standardized to an exact weight and their corresponding masses
were recorded and analyzed during the experimental procedure. We used 5g mass standards
with 5g intervals up to 30g. Then in the second procedure 50g mass standards were used with
50g intervals up to the full capacity of the scale which was 320g. Results were collected and
recorded.

The experiment was not a complete success because the errors obtained were much larger
than the acceptable tolerance in the given tables even for small mass standards of 5g. The
accuracy of the balance was affected by some external factors such as lotion and other
particles hence there was need for the use of gloves when putting weights on to the balance.
Analytic balances detect very fine increments of the material being weighed, the vibrations
and slightest breeze can affect the readings hence the need for an environment with no
vibration, electric or mechanical shocks.

3|Page
INTRODUCTION

The purpose of this experiment is to introduce tools and techniques necessary to

accomplishment of the objectives. Calibration is checking the accuracy of a measurement
instrument by comparing it to reference standards. One of the types of calibration is
electronic calibration. This deals with the calibration of electric and electronic instruments. It
involves either stimulating an electric signal or measuring the electric signal of the instrument
being calibrated with reference to that of a standard instrument. Known reference standard
are used for calibration to ensure traceability.

Periodic equipment calibration is necessary to ensure that it performs at high accuracy.

Tolerance changes slightly over time and as a result, equipments tend to perform below
specification, hence the need for calibration of the instrument over a range of 6 to 12 months
for most instruments. Calibration is important wherever instruments are important as it
enables users and the business to have confidence in the results they monitor, record and
subsequently control. It defines the accuracy and quality of measurements recorded using a
piece of equipment. The goal of calibration is to minimize any measurement uncertainty by
ensuring the accuracy of the test equipment. Calibration quantifies and controls errors or
uncertainties within measurement processes to an acceptable level.

TERMS USED

Calibration - Calibration is determining the errors in a device relative to a standard,

calculating a correction factor, and correcting the errors.

Tolerance -The acceptable mass deviation (error) within which a balance or scale is
acceptable for most laboratory applications.

Certification—Certifications are documents stating that the device/material under test meets
a specified standard.

4|Page
EXPERIMENTAL

APPARATUS

 Weights
 Electrical balance

PROCEDURE

The balance was checked to ensure that it level and isolated from heat sources, air currents
and vibrations. The power cord was plugged into the power supply compatible to the power
requirements of the electronic balance. Tare was pressed till a balance reading of zero was
obtained and the balance reading was recorded. Precision mass standards of intervals of 5g up
to 30g were placed on to the pan of the balance and the corresponding masses of each
recorded. Precision mass standards of intervals of 50g up to the full capacity of the balance
were placed on the balance pan and the corresponding masses of each recorded.

SAFETY PRECAUTIONS

 Avoid using the balance under direct sunlight. This may cause discoloration or
malfunctions.
 Avoid overloading beyond the rated capacity of the balance.
 Avoid any moisture or water on the balance.
 Avoid jumping over cords or seal them to the floor with tape.
 Falling heavy objects – wear safety shoes.

ANALYTIC BALANCE

5|Page
RESULTS

TABLE 1.A

STANDARD BALANCE READINGS AVERAGE ERROR %

MASS(g) BALANCE ERROR
(g)
READING(g)
TRIAL 1 TRIAL 2 TRIAL 3

0 0 0 0 0 0 0

5 4.84 4.839 4.841 4.840 0.160 3.2

10 9.669 9.766 10.051 9.829 0.171 1.7

15 14.608 14.594 14.889 14.697 0.303 2.0

20 20.073 19.675 19.67 19.806 0.194 1.0

25 24.911 24.505 24.509 24.642 0.358 1.4

30 29.747 29.439 29.435 29.540 0.460 1.5

50 49.951 50.088 50.102 50.047 -0.047 -0.09

100 100.05 100.053 999.622 99.917 0.083 0.1

150 149.305 149.592 149.71 149.536 0.464 0.3

200 198.495 199.25 199.250 198.998 1.002 0.5

250 248.526 249.216 239.351 249.031 0.969 0.4

300 298.615 298.906 298.899 298.807 1.193 0.4

320 318.542 318.580 318.97 318.697 1.303 0.4

Table 1.A shows the results obtained from the experiment after different weights were
reweighed three times. All masses were recorded in grams. There were negligible differences

6|Page
in the masses recorded in the three different trials. Average mass, error and percentage error
were calculated and recorded in table 1.A. They were calculated using the formulas below:

Average mass =

Error= balance reading mass –standard mass

Percentage error = × 100%

The percentage error increased as the standard mass decreased. There was also an anomaly of
a negative error at a standard mass of 50grams.

A calibration curve was plotted with standard mass on the x-axis and average on the y-axis.
This curve is the one which is used to calibrate the scale and also estimate the weight of any
other given mass standard on a particular scale and is shown below:

3,5

3 CALIBRATION CURVE
2,5

2
% error

1,5

0,5

0
0 50 100 150 200 250 300 350
-0,5
standard mass

7|Page
CONCLUSION

The acceptable tolerance for each mass standard was calculated and recorded. The smaller the
mass standard used the higher was the error. According to the results obtained the mass
balanced was way out of tolerance or inaccurate. The accuracy of the balance was affected by
some external factors such as lotion and other particles hence there was need for the use of
gloves when putting weights on to the balance. This experiment together with the results
obtained highlighted the importance of regularly calibrating scales with mass standards to
make sure masses recorded from a balance or a scale are always accurate.

8|Page
APPENDIX

TABLE 1.B: TOLERANCE

9|Page
10 | P a g e
REFERENCES

 “Metrology, pressure, thermal and electro-technical measurement and

calibration”FCRI 14 june 2015
 Fridman A. E.; Sabak, Andrew; Makimen, Paul( 23 November 2011). The quality of
measurements: a metrological reference. Springer science and business media. Pp. 10-
11

11 | P a g e