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

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Presentation on theme: "Calibration of Balance Sri Lanka 1 Nihal Gunasekara Bangladesh BEST Programme."— Presentation transcript:

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

2 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 2 Bangladesh BEST Programme

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

4 Micro Balance 4 Bangladesh BEST Programme

5 Semi Micro Balance Balance with a resolution of 10 microgram 5 Balance with a resolution of 0.1 microgram Bangladesh BEST Programme

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

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

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

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

10 Standby Operating state of an electronic instrument where one part is switched off for energy saving reasons 10 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 Bangladesh BEST Programme

11 11 Different accuracy classes of mass Bangladesh BEST Programme

12 Repeatability  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 12 Bangladesh BEST Programme

13 Reproducibility  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 13 Bangladesh BEST Programme

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

15 Influence factor 15 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 Primary Stability of reading under constant load Secondary Accelerometer measurements Changes forces on the weighing machine due to acceleration Various, Eg. Machinery, roads, railways, aircraft operator Vibration causes damages VibrationEnvironmental PrecautionsTest for effectEffectSourceParameterInfluence factor Bangladesh BEST Programme

16 Influence factor 16 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 Temperature monitoring instruments Temperature changes and differentials can change the weighing machine response, cause convection effects and change buoyancy Sunlight, heating systems, operator’s body, greenhouse heating in the weighing chamber Temperature: air, weight, weighing machine Environmental PrecautionsTest for effectEffectSourceParameterInfluence factor Bangladesh BEST Programme

17 Influence factor 17 Avoid liquid water in the working area unless rh is too low. Air conditioning, humidity controller Rh monitoring instruments Buoyancy, absorbed moisture, condensation Air supply,air conditioning, changes in activity levels HumidityEnvironmental PrecautionsTest for effectEffectSourceParameterInfluence factor Bangladesh BEST Programme

18 Influence factor 18 PrecautionsTest for effectEffectSourceParameterInfluence factor Avoid temperature gradients. draught free working space, enclose weighing machines Primary Stability of reading under constant load Secondary Enclose weighing machine and observe change of reading stability Varies force on weighing machine Air conditioning, wind, convection, operator movement AirflowEnvironmental Bangladesh BEST Programme

19 Influence factor 19 PrecautionsTest for effectEffectSourceParameterInfluence factor 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 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) Change of current in force compensation coil, direct attraction to/from surrounding structure Motion- dependent restoring forces Constructional steelwork, ferromagnetic weight (s) electrical induction earth’s magnetic field, moving-coil meters Magnetic Environmental Bangladesh BEST Programme

20 20 RepeatabilityLoad cell hysteresis RepeatabilityElectrical Interference ZeroMains fluctuation Sensitivity, Zero, RepeatabilityIncorrect horizontal support RepeatabilityMechanical errors Type of errorSource of error Bangladesh BEST Programme

21 21 ACCURACY CLASS (OIML R111-1 :2004) 0.003 Bangladesh BEST Programme

22 Lowest class of weights required for different types of weighing machine 22 E2 F2M1M2 1 kg to 30kg E2 F1/E2F2M1 200g to 1 kg E2F1F2M1M230kg to 100kg E2F1F2M1 Up to 200g E2F1M1/F2M2Above 100 kg 0.01mg or less 0.1mg1mg10mg 100mg 1g10g100g Resolution Capacity Bangladesh BEST Programme

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

24 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. 24 Bangladesh BEST Pregramme

25 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. 25 Before use a Balance Bangladesh BEST Programme

26 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 26 Bangladesh BEST Programme

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

28 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” 28 Bangladesh BEST Programme

29 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 29 Bangladesh BEST Programme

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

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

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

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

34 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 34 Bangladesh BEST Programme

35 Departure from Nominal Value: 1 Divide the range into at least 10 equally spaced steps 2 The masses corresponding to M, 2M, 3M, 4M, 5M, 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. 35 Bangladesh BEST Programme

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

37 Departure from Nominal Value: Average zero reading z i = (z 1 + z 2 )/ 2 Average mass reading r i = (r 1 + r 2 )/ 2 Difference d i = r i – z i Correction c i = M i – d i M i is the conventional value of the mass 37 Bangladesh BEST Programme

38 Correction to Balance Reading Pan LoadConv. Value M i ReadingMeanDifference r i - z i Correction M i - d i M- 100100.02 0.00 100.00 0.00 100.02 0.00 100.01 0.01 2M 3M 4M 5M 6M 7M 8M 9M 10M Bangladesh BEST Programme

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

40 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” 40 Bangladesh Best Programme

41 Off Centre Loading 41 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 3 2 4 5 1 Bangladesh BEST Programme

42 Off Centre Loading: 42 Center (g) 100.0000-100.0000=0.0000 Left (g) 100.0001-100.0000=0.0001 Back (g) 100.0000-100.0000=0.0000 Right (g) 99.9999-100.0000= -0.0001 Front (g) 100.0001-100.0000=0.0001 Max Difference =0.0002 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 Bangladesh BEST Programme

43 Off Centre Loading : 43 0.0002- 0.00010.00010.00000.00010.0000 Maximum Difference (g) Right(g)Left(g)Back(g)Front(g)Centre(g) Mass of 100g was moved to various positions on the pan. The balance readings obtained relative to the centre reading 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 Bangladesh BEST Programme

44 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” 44 Bangladesh BEST Programme

45 Hysteresis Perform the test at one point about mid range Zero the balance and record the reading z 1 Place a mass M 1 on the plan and record the reading r 1 Add extra mass M 2 to bring the balance close to full range Remove the extra mass M 2 and record the reading with the mass M 1 still on the pan Remove the mass M 1 and record the reading r 2 Repeat above steps three times Take the average of three readings 45 Bangladesh BEST Programme

46 Hysteresis Mass M = g 46 Bangladesh BEST Programme Pan LoadReading 1Reading 2Reading 3 Zero ( z 1 ) M ( m 1 ) M + M 1 M ( m 2 ) Zero ( z 2 ) m 1 - m 2 z 1 - z 2

47 Hysteresis: 47 0.1100 0.00 Hysteresis Error(mg)Pan Load (g) Bangladesh BEST Programme

48 Hysteresis: 48 Hysteresis error Bangladesh BEST Programme

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

50 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 50 Bangladesh BEST Programme

51 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 51 Bangladesh BEST Programme

52 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 z 1 Set the "1" on the dial to be tested, place a calibrated mass, release the pan and record the reading m 1a Remove the mass, replace it and record the reading m 1b Return the dial to zero, remove the mass from the pan and record the zero z 2 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 52 Bangladesh BEST Programme

53 Calibration of Triple Beam Balances 53 Bangladesh BEST Programme

54 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 54 Bangladesh BEST Programme

55 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 55 Bangladesh Best Programme

56 Triple Beam Balance Repeatability of readings: Set the reading to zero without any mass on the pan Record the zero reading z i of the balance without any mass on the pan Place the mass M on the pan and record the mass reading m i 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 56 Bangladesh BEST Programme

57 Triple Beam Balance 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 z 1 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 m i Remove the mass(es), place it back on the pan and record the mass reading m i2 Remove the mass(es) and record the zero reading z i+1 Repeat the above steps for the remaining points ( 2M, 3M,….) 57 Bangladesh Best Programme

58 Weighing Scale (digital or analogue) 58 Bangladesh Best Programme 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 F 1 59 Bangladesh BEST Programme Nominal ValueConventional ValueUncertainty k=2Max. Perm. Error 1 mg1 mg – 0.001 mg0.006 mg±0.02 mg 2 mg2 mg + 0.011 mg0.006 mg±0.02 mg 5 mg5 mg+0.002 mg0.006 mg±0.02 mg 20 mg20 mg – 0.005 mg0.01 mg±0.03 mg 50 mg50 mg + 0.009 mg0.012 mg±0.04 mg 100 mg100 mg + 0.011 mg0.015 mg±0.05 mg 500 mg500 mg + 0.033 mg0.025 mg±0.08 mg 1 g1 g – 0.028 mg0.03 mg±0.1 mg 2 g2 g + 0.022 mg0.04 mg±0.12 mg 20 g20 g + 0.009 mg0.08 mg±0.25 mg 50 g50 g – 0.12 mg0.1 mg±0.3 mg 100 g100 g – 0.22 mg0.15 mg±0.5 mg 200 g200 g + 0.04 mg0.3 mg±1 mg Issued by an accredited laboratory (DKD)

60 Thank you 60 Bangladesh BEST Programme


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