1. Calibration of Balance
Bangladesh BEST Programme
Calibration of Balance
Sri Lanka
Nihal Gunasekara

2. Types of Balances Electromagnetic force balance (Top loading)
Bangladesh BEST Programme
Types of Balances
Electromagnetic force balance (Top loading)
Single-pan, two-knife-edge balance
Two-pan, three-knife-edge balance
Triple beam balance
Weighing scale

3. Bangladesh BEST Programme
Analytical Balance
Balance with an enclosed weighing chamber and a resolution 0.01 or 0.1 mg
Micro Balance
Balance with a resolution of 1 microgram

4. Bangladesh BEST Programme
Micro Balance

5. Ultra (Super) Micro Balance
Bangladesh BEST Programme
Semi Micro Balance
Balance with a resolution of 10 microgram
Ultra (Super) Micro Balance
Balance with a resolution of 0.1 microgram

6. Resolution or Discrimination
Bangladesh BEST Programme
Resolution or Discrimination
The smallest change in mass which can be detect by the balance
Sensitivity
This is a measure of the ability of the balance
to detect changes in the load applied to it

7. Response time Stability
Bangladesh BEST Programme
Response time
Time taken for the weighing instrument to indicate the value of a change in load
Stability
A measure of the time for which the reading on the balance remains unchanged

8. Correction = True Value - Reading Error = Reading - True Value
Bangladesh BEST Programme
Correction
Correction = True Value - Reading
Error
Error = Reading - True Value

9. Departure From Nominal Value
Bangladesh BEST Programme
Departure From Nominal Value
The amount by which the reading on an instrument depart from its nominal value
Hysteresis
The indications of a measuring instrument when the same value of the quantity measured is reached by increasing or decreasing that quantity

10. Standby Accuracy class. (mass)
Bangladesh BEST Programme
Standby
Operating state of an electronic instrument where one part is switched off for energy saving reasons
Accuracy class. (mass)
Legal metrology term. Classification of weights for calibration purposes by OIML R111-1 weights of Accuracy class E1, E2, F1, F2, M1, M2, M3 from 1 mg to 50 kg

11. Different accuracy classes of mass
Bangladesh BEST Programme
Different accuracy classes of mass

12. Repeatability Bangladesh BEST Programme
Closeness of the agreement between the results of successive measurements of the same measurement carried out under the same conditions of measurement.
Repeatability condition include :
the same observer
the same measuring instrument, used under the same conditions
the same location
repetition over a short period of time

13. Reproducibility Bangladesh BEST Programme
Closeness of the agreement between the results of measurements of the same measurement carried out under changed conditions of measurement.
A valid statement of reproducibility requires specification of the conditions change
The changed conditions may include
principle of measurement
method of measurement
observer
measuring instrument
reference standard
location
conditions of use
Time

14. Influence Factors Air movements and heat sources
Bangladesh BEST Programme
Influence Factors
Air movements and heat sources
Support surfaces and vibration
Electrical and electromagnetic interference
Magnetic effects
Buoyancy effects

15. Influence factor Bangladesh BEST Programme Influence factor Parameter
Source
Effect
Test for effect
Precautions
Environmental
Vibration
Various, Eg. Machinery, roads, railways, aircraft operator
Vibration causes damages
Changes forces on the weighing machine due to acceleration
Primary
Stability of reading under constant load
Secondary
Accelerometer measurements
Use of a high-mass support, set on a solid surface, for the weighing machine, independent of the adjacent flooring, Eg fixed to bedrock
Note : low frequency, vibration is likely to be more serious in its effects than high (acoustic) frequencies
Rubber pads used to damp high frequencies may pass low frequency vibration, and may cause tilting of the weighing machine

16. Influence factor Bangladesh BEST Programme Influence factor Parameter
Source
Effect
Test for effect
Precautions
Environmental
Temperature: air, weight, weighing machine
Sunlight, heating systems, operator’s body, greenhouse heating in the weighing chamber
Temperature changes and differentials can change the weighing machine response, cause convection effects and change buoyancy
Temperature monitoring instruments
Avoid direct sunlight and other connections to the external environment; avoid changes in heat and lighting input. Leave balance cases ajar when not in use. Avoid excessive handling of equipment during weighing. Allow weighted object to acclimatize

17. Influence factor Bangladesh BEST Programme Influence factor Parameter
Source
Effect
Test for effect
Precautions
Environmental
Humidity
Air supply ,air conditioning, changes in activity levels
Buoyancy, absorbed moisture, condensation
Rh monitoring instruments
Avoid liquid water in the working area unless rh is too low .
Air conditioning, humidity controller

18. Influence factor Bangladesh BEST Programme Influence factor Parameter
Source
Effect
Test for effect
Precautions
Environmental
Airflow
Air conditioning, wind, convection, operator movement
Varies force on weighing machine
Primary
Stability of reading under constant load
Secondary
Enclose weighing machine and observe change of reading stability
Avoid temperature gradients. draught free working space, enclose weighing machines

19. Influence factor Bangladesh BEST Programme Influence factor Parameter
Source
Effect
Test for effect
Precautions
Environmental
Magnetic
Constructional steelwork, ferromagnetic weight (s) electrical induction earth’s magnetic field, moving-coil meters
Change of current in force compensation coil, direct attraction to/from surrounding structure Motion-dependent restoring forces
Primary
Use a magnet to check for induced reading changes
Secondary
Monitoring readings when weights are rotated and at varying heights above the weight receptor (place on/under non-magnetic mount)
Avoid weights with residual magnetism (de-gauss) Test with compass or gaussmeter Limit magnetic permeability of weights weighed check for magnetic fields with gaussmeter Screen with mumetal

20. Type of error Source of error Bangladesh BEST Programme Repeatability
Load cell hysteresis
Electrical Interference
Zero
Mains fluctuation
Sensitivity, Zero, Repeatability
Incorrect horizontal support
Mechanical errors
Type of error
Source of error

21. ACCURACY CLASS (OIML R111-1 :2004)
Bangladesh BEST Programme
ACCURACY CLASS (OIML R111-1 :2004)
0.20
0.06
0.020
0.006
1 mg
0.003
5 mg
0.25
0.08
0.025
0.008
10 mg
0.4
0.12
0.04
0.012
0.004
50 mg
1.6
0.5
0.16
0.05
0.016
0.005
100 mg 10
3.0
1.0
0.3
0.10
0.03
0.010
1 g 12
4.0
1.2
2 g 16
5.0
5 g 20
6.0
2.0
0.6
10 g 30 3
0.030
50 g 50 5
100 g
100
1. 0
200 g
500
160
1 kg
1000
300
2 kg
2500
800
250 80 25
8.0
2.5
5 kg
5000
1600
10 kg
Class M3
Class M2
Class M1
Class F2
Class F1
Class E2
Class E1
Tolerance in mg
Nominal value
0.003

22. Bangladesh BEST Programme
Lowest class of weights required for different types of weighing machine
Capacity
Resolution
100g
10g 1g
100mg
10mg
1mg
0.1mg
0.01mg or less
Up to 200g M1 M1 F2 F1 E2
200g to 1 kg M1 M1 F2
F1/E2 E2 E2
1 kg to 30kg M2 M2 M1 F2 E2 E2 E2
30kg to 100kg M2 M1 F2 F1 E2
Above 100 kg M2
M1/F2 F1 E2

23. Calibration of Top Loading and Analytical Balances
Bangladesh BEST Programme
Calibration of Top Loading and Analytical Balances

24. Before use a Balance…………
Bangladesh BEST Pregramme
Before use a Balance…………
Keep the Balance power on appropriate time to warm up.
Clean the balance as best as no contamination on the balance pan.
If it is applicable, level the balance before use.
Don’t move the balance after the calibration.
Lint or any other soft gloves should be worn by the user.
A pair of forceps or a pair tweezers with thermal insulating ends should be used to lift and place weights.

25. Before use a Balance Bangladesh BEST Programme
Make sure with the soft placement of weights on the balance pan as level best of possible.
Readings should be taken after the balance is stabilized well.
The place should be free from vibration.
Any other relevant precaution practiced by the user.

26. Test 2 - Repeatability of Reading
Bangladesh BEST Programme
Balance Calibration
The calibration of the electromagnetic force compensation balance consists of the following tests:
Test 1 - Scale Value
Test 2 - Repeatability of Reading
Test 3 - Departure from Nominal Value
Test 4 - Off centre Loading
Test 5 – Hysteresis

27. Procedure – Balance Operating Manual
Bangladesh BEST Programme
Scale Value
Internal Scale Adjustment –Internal Mass
External Scale Adjustment – External Mass
Procedure – Balance Operating Manual

28. Repeatability of Reading
Bangladesh BEST Programme
Repeatability of Reading
Objective of Measurement :
The repeatability test is carried out to determine the ability of the balance to give under defined conditions of use closely similar responses for repeated measurements
The balance Standard Deviation is the “repeatability of measurement”

29. Repeatability of Reading
Bangladesh BEST Programme
Repeatability of Reading :
M 1 -Set the reading to zero without any mass on the pan
M 2 - Record the zero reading of the balance (z)
M 3 - Place the mass on the pan and record the reading (r)
M 4 - Remove the mass from the pan
M 5 – Repeat M2 to M4 ten times
during the process the balance should not be zeroed

30. Repeatability of Reading:
Bangladesh BEST Programme
Repeatability of Reading:
Performed at three points :
Near zero
Near half load
Near full load

31. DATA RECORDING Mass 1 : Mass 2: Mass 3: Bangladesh BEST Programme No 1
Zero reading
(z)
Mass reading
(r)
Corr.
reading
(r-z)
Corr. reading
(r ) 1 2 3 4 5 6 7 8 9 10

32. Repeatability of Reading
Bangladesh BEST Programme
Repeatability of Reading
Mass 1: Mass 2: Mass 3 :
Mean value :
Std. Dev. ( σ ) :
Max. Diff :
Uncer. Type A :

33. Repeatability of Reading
Bangladesh BEST Programme
Repeatability of Reading
Repeat three different values of M ; near zero, half maximum and maximum load.
Load on Pan
(g)
Standard Deviation of Reading (mg)
Maximum Difference Between Successive Readings (mg)
0.05
100
200
0.067
0.052
0.2
0.1

34. Departure from Nominal Value:
Bangladesh BEST Programme
Departure from Nominal Value:
Objective of Measurement :
“The departure from nominal value measurements are carried out to determine the deviation of the balance reading from the expected value”
This is the Correction to Balance Reading

35. Departure from Nominal Value:
Bangladesh BEST Programme
Departure from Nominal Value:
1 Divide the range into at least 10 equally spaced steps
2 The masses corresponding to M, 2M, 3M, 4M, M, 6M etc. until the capacity of balance is reached
3 In addition choose four more test points corresponding to 20 %, 40 %,60%and 80 % of the first step for single range.

36. Departure from Nominal Value:
Bangladesh BEST Programme
Departure from Nominal Value:
1 - Read the zero z1
2 - Place the weight on the pan &record reading r1
3 – Remove the weight momentarily and place it back on the pan and note the new reading r2
4 - Remove the weight and read the zero z2
5 – Repeat 1 to 4 for weights of masses 2M,3M,4M,5M etc until the capacity of balance is reached

37. Departure from Nominal Value:
Bangladesh BEST Programme
Departure from Nominal Value:
Average zero reading zi = (z1 + z2 )/ 2
Average mass reading ri = (r1 + r2 )/ 2
Difference di = ri – zi
Correction ci = Mi – di
Mi is the conventional value of the mass

38. Correction to Balance Reading
Bangladesh BEST Programme
Correction to Balance Reading
Pan Load
Conv. Value Mi
Reading
Mean
Difference
ri - zi
Correction
Mi - di
M- 100
100.02
0.00
100.00
100.01
0.01 2M 3M 4M 5M 6M 7M 8M 9M
10M

39. Departure from Nominal Value:
Bangladesh BEST Programme
Departure from Nominal Value:
Reading
(g)
Correction(mg)
Expanded Uncertainty k=2
+(mg)
Before the Calibration
After the Calibration 4 8 12 16 20 40 60 80
100
120
140
160
180
200
220 --
0.2
0.4
0.6
0.5
0.0
-0.1
0.1
-0.0
-0.2
-0.3
0.096
0.097
0.098
0.099
0.10
0.11

40. Objective of Measurement :
Bangladesh Best Programme
Off Centre Loading:
Objective of Measurement :
“The off center loading is carried out to find the variation in the displayed weighted as the object is moved to various positions on the weighing pan”

41. Off Centre Loading Bangladesh BEST Programme
This test to find the variation of the reading for several place of the balance pan. Test should be done for rectangular type balance pans and as well as for circular type balance pans.
A single weight should be used 4 3 1 5 2

42. Off Centre Loading: Bangladesh BEST Programme
Place a mass on the centre of the pan and move it successively to the front rear, left and right positions ( position being 2/3 of the distance between the centre and the lip of the pan) on the pan recording the reading each time
Back (g)
=0.0000
Center (g)
=0.0000
Right (g) =
Left (g)
=0.0001
Max Difference = g
Front (g)
=0.0001

43. Maximum Difference (g)
Bangladesh BEST Programme
Off Centre Loading:
Mass of 100g was moved to various positions on the pan. The balance readings obtained relative to the centre reading
0.0002
0.0001
0.0000
Maximum Difference (g)
Right(g)
Left(g)
Back(g)
Front(g)
Centre(g)
Place a mass on the centre of the pan and move it successively to the front rear, left and right positions ( position being 2/3 of the distance between the centre and the lip of the pan) on the pan recording the reading each time

44. Hysteresis: Objective of Measurement :
Bangladesh BEST Programme
Hysteresis:
Objective of Measurement :
“The hysteresis measurements are performed to determine the difference in the indication at the same load , depending upon the direction of approach to that load ie increasing or decreasing the load”

45. Hysteresis Zero the balance and record the reading z1
Bangladesh BEST Programme
Hysteresis
Perform the test at one point about mid range
Zero the balance and record the reading z1
Place a mass M1 on the plan and record the reading r1
Add extra mass M2 to bring the balance close to full range
Remove the extra mass M2 and record the reading with the mass M1 still on the pan
Remove the mass M1 and record the reading r2
Repeat above steps three times
Take the average of three readings

46. Hysteresis Mass M = g Bangladesh BEST Programme Pan Load Reading 1
Pan Load
Reading 1
Reading 2
Reading 3
Zero ( z1 )
M ( m1 )
M + M1
M ( m2 )
Zero ( z2 )
m1 - m2
z1 - z2

47. Hysteresis: 0.1 100 0.0 Hysteresis Error(mg) Pan Load (g)
Bangladesh BEST Programme
Hysteresis:
0.1
100
0.0
Hysteresis Error(mg)
Pan Load (g)

48. Bangladesh BEST Programme
Hysteresis:
Hysteresis error

49. Calibration of Single Pan two Knife Edge Balances
Bangladesh BEST Programme
Calibration of Single Pan two Knife Edge Balances

50. Test 1 - Repeatability of Reading
Bangladesh BEST Programme
Balance Calibration
The calibration of the single pan two knife edge balance consists of the following tests:
Test 1 - Repeatability of Reading
Test 2 - Departure from Nominal Value
Test 3 – Built-in-Mass
Test 4 - Off centre Loading
Test 5 – Hysterisis

51. Bangladesh BEST Programme
Balance Calibration
The calibration of the single pan two knife edge balance consists of the following tests:
Test 1 - Repeatability of Reading- same as electronic balance
Test 2 - Departure from Nominal Value- same as electronic balance
Test 3 – Built-in-Mass
Test 4 - Off centre Loading- same as electronic balance
Test 5 – Hysteresis- same as electronic balance

52. Balance Calibration The procedure to determine the Built-in- Mass
Bangladesh BEST Programme
Balance Calibration
The procedure to determine the Built-in- Mass
With all dials set to the zero and no load on the pan, release the balance and record the reading z1
  Set the "1" on the dial to be tested, place a calibrated mass, release the pan and record the reading m1a
 Remove the mass , replace it and record the reading m1b
 Return the dial to zero, remove the mass from the pan and record the zero z2
 Repeat the above steps for all dial settings of the balance (i.e. 2 , 3, 10 , 20 ,…………..90 , 100 , 200 )
Follow the same procedure used for linearity test to determine the correction

53. Calibration of Triple Beam Balances
Bangladesh BEST Programme
Calibration of Triple Beam Balances

54. Test 1 - Repeatability of Reading - same as electronic balance
Bangladesh BEST Programme
Balance Calibration
The calibration of triple beam balances consists of the following tests:
Test 1 - Repeatability of Reading - same as electronic balance
Test 2 - Departure from Nominal Value (Linearity Test) -
same as electronic balance

55. Triple Beam Balance Before the calibration
Bangladesh Best Programme
Triple Beam Balance
Before the calibration
Clean the weighing pan and other parts of the balance taking due care
Level the balance
Exercise the balance by making several weighing

56. Triple Beam Balance Repeatability of readings:
Bangladesh BEST Programme
Triple Beam Balance
Repeatability of readings:
Set the reading to zero without any mass on the pan
Record the zero reading zi of the balance without any mass on the pan
 Place the mass M on the pan and record the mass reading mi
Remove the mass M from the pan
Repeat the above steps ten times (The balance should not be zeroed during the series of readings)
Repeat for this for near zero, half load and near maximum

57. Triple Beam Balance Bangladesh Best Programme
Select a minimum of 10 equally spaced points ( M , 2M ,…..10M ) on the measuring range in such a way they cover the entire range or the part of the measuring range to be calibrated. In addition four test points corresponding to 20%,40%,60% and 80 % of the first step
Record the zero reading z1
Set the slider scale to the first step on the measuring range (M) , place the calibrating mass(es) on the pan until the balance comes to equilibrium and record the mass reading mi
 Remove the mass(es), place it back on the pan and record the mass reading mi2
Remove the mass(es) and record the zero reading zi+1
 Repeat the above steps for the remaining points ( 2M , 3M ,….)

58. Weighing Scale (digital or analogue)
Bangladesh Best Programme
Weighing Scale (digital or analogue)
The calibration of weighing scales consists of the following tests:
Test 1 - Repeatability of Reading - same as electronic balance
Test 2 - Departure from Nominal Value (Linearity Test) -
same as electronic balance

59. Calibration Results of a Set of Weights –Class F1
Bangladesh BEST Programme
Calibration Results of a Set of Weights –Class F1
Nominal Value
Conventional Value
Uncertainty k=2
Max. Perm. Error
1 mg
1 mg – mg
0.006 mg
±0.02 mg
2 mg
2 mg mg
5 mg
5 mg mg
20 mg
20 mg – mg
0.01 mg
±0.03 mg
50 mg
50 mg mg
0.012 mg
±0.04 mg
100 mg
100 mg mg
0.015 mg
±0.05 mg
500 mg
500 mg mg
0.025 mg
±0.08 mg
1 g
1 g – mg
0.03 mg
±0.1 mg
2 g
2 g mg
0.04 mg
±0.12 mg
20 g
20 g mg
0.08 mg
±0.25 mg
50 g
50 g – 0.12 mg
0.1 mg
±0.3 mg
100 g
100 g – 0.22 mg
0.15 mg
±0.5 mg
200 g
200 g mg
0.3 mg
±1 mg
Issued by an accredited laboratory (DKD)

60. Bangladesh BEST Programme
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