1. Standard Weights and Classes of Balances
Bangladesh BEST Programme
Standard Weights and Classes of Balances
Nihal Gunasekara
Sri Lanka

2. Primary Measurement Standard
Bangladesh BEST Programme
Primary Measurement Standard
Definition:
Measurement standard established using a primary reference measurement procedure, or created an artifact, chosen by convention
The international prototype kilogram made from platinum iridium alloy and maintained at the BIPM - France
The kilogram remains to be the only artifact standard of the SI system of units

3. Primary Measurement Standard
Bangladesh BEST Programme
Primary Measurement Standard
Redefining the Kilogram through the Avogadro Constant
It is proposed to redefine the kilogram in terms of the Avogadro constant NA
By definition an Avogadro number of carbon-12 atoms weight exactly 12g

4. Secondary Measurement Standards
Bangladesh BEST Programme
Secondary Measurement Standards
Definition:
Measurement standard established through calibration with respect to a primary measurement standard for a quantity of the same kind
Prototype 1kg Secondary Standard

5. Reference Measurement Standards
Bangladesh BEST Programme
Reference Measurement Standards
Definition:
Measurement standard designated for the calibration of other measurement standards for quantities of a given kind in a given organization or at a given location
E2 Set of Weights

6. Working Measurement Standards
Bangladesh BEST Programme
Working Measurement Standards
Definition:
Measurement standard that is used routinely to calibrate or verify measuring instruments or measuring systems
M1 Set of Weights

7. Travelling Measurement Standards
Bangladesh BEST Programme
Travelling Measurement Standards
Definition:
Measurement standard some times of special construction, intended for transport between different locations
Portable battery operated caesium-133 frequency measurement standard

8. W=mg where g is the acceleration due to gravity
Bangladesh BEST Programme
Mass and Weight
Mass- Amount of matter in an object.
F = m x a
(Force) = (mass) x (acceleration)
Weight- Force experienced by it due to the earth’s gravity
W = m x g
(weight) = (mass) x (acceleration due to gravity) M
W=mg where g is the acceleration due to gravity

9. Mass Standards- Types of Masses
Bangladesh BEST Programme
Mass Standards- Types of Masses
Masses are classified into categories depending on : Material and Construction
Main Types :
Integral Masses – non magnetic stainless steel
Non-integral or two piece masses - non magnetic stainless steel (can be adjusted)
Masses made from brass – plated or un plated ( integral or non-integral )
Cast iron masses – usually painted

10. Mass Standards- Classes of Masses
Bangladesh BEST Programme
Mass Standards- Classes of Masses
Classification of mass standards based on :
Conventional value and nominal value :
Deviation = Conventional value – Nominal value
OIML classification system is widely used
OIML R
Masses are classified as : E1 E2 F1 F2 M1 M2 M3

11. Bangladesh BEST Programme
ACCURACY CLASS
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
50 g 50
100 g
100
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 3
0.003

12. Different Classes of Masses
Bangladesh BEST Programme
Different Classes of Masses

13. Types and Classes of Balances
Bangladesh BEST Programme
Types and Classes of Balances
Weighing balances are classified into different types
The main categories are :
Triple beam balances
Two pan, three knife – edge balances
Single pan, two knife – edge balances
Electromagnetic force – compensation balances

14. Triple Beam Balance Bangladesh BEST Programme
A triple beam balance is a type of balance commonly used in the laboratory to determine the mass (by weight comparison) of samples. It is called a triple beam because of the three beams on the scale that are used for determining the weight of the item. The first beam measures 0 to 10 grams, the middle beam weighs in 10 gram increments and the far beam weighs in 100 g increments.

15. Two pan three knife edge
A schematic of a two pan three knife-edge balance is shown below. The balance consist of a main beam carrying two pans at its ends. The beam has a central knife edge resting on a bearing pad when the balance is in operation. The two pans are supported by knife –edges at the extremities of the beam. All there knife edges lie in a plane. The central knife edge is normally equi-distant from the from the pan knife edges and due to this reason these balances are also known as equal arm balances.
A schematic of a two pan three knife-edge balance is shown below. The balance consist of a main beam carrying two pans at its ends. The beam has a central knife edge resting on a bearing pad when the balance is in operation. The two pans are supported by knife –edges at the extremities of the beam. All there knife edges lie in a plane. The central knife edge is normally equi-distant from the from the pan knife edges and due to this reason these balances are also known as equal arm balances.
A schematic of a two pan three knife-edge balance is shown below. The balance consist of a main beam carrying two pans at its ends. The beam has a central knife edge resting on a bearing pad when the balance is in operation. The two pans are supported by knife –edges at the extremities of the beam. All there knife edges lie in a plane. The central knife edge is normally equi-distant from the from the pan knife edges and due to this reason these balances are also known as equal arm balances.
A schematic of a two pan three knife-edge balance is shown below. The balance consist of a main beam carrying two pans at its ends. The beam has a central knife edge resting on a bearing pad when the balance is in operation. The two pans are supported by knife –edges at the extremities of the beam. All there knife edges lie in a plane. The central knife edge is normally equi-distant from the from the pan knife edges and due to this reason these balances are also known as equal arm balances.
Bangladesh BEST Programme
Two pan three knife edge S
Single pan three knife balance consist of main beam carrying two pans at its ends. The beam has a central knife edge resting on a bearing pad when the balance is in operation The two pans are supported by knife-edges at the extremities of the beam. All three knife edges lie in a plane. The central knife edge is normally equi-distant from the pan knife edges and due to this reason these balance are also known as equal arm balances.
This type of balance is mostly used in high precision metrology laboratories for calibration of secondary level masses

16. Single-Pan, two knife edge
Bangladesh BEST Programme
These instruments fall into two categories usually termed top loading and analytical balances. In the analytical balance the load is suspended below the balance arm and the beam is arrested during loading and unloading of the pan. In the top loading balance the pan is supported above the beam by a parallelogram linkage and there is usually no arresting mechanism. Both types of balance are usually critically damped. Most balances have built in masses attached to the pan assembly so that whenever a load is placed on the pan an equivalent mass is lifted from the pan. This means that the load to be supported by the knife edges is fairly constant and balances of this type are often referred to as constant load balances.

17. Single Pan Two Knife Edge
Bangladesh BEST Programme
Single Pan Two Knife Edge

18. Electromagnetic force compensated balance
Bangladesh BEST Programme
Electromagnetic force compensated balance
An electronic force is generated, via a current carrying coil in a magnetic field, to oppose the out of balance force on a knife edge balance and return the beam to a reference horizontal position. The force is usually measured by reference to the current in the coil. The balance is usually single pan or top loading.

19. Electromagnetic Force Compensated Balance
Bangladesh BEST Programme
Electromagnetic Force Compensated Balance

20. Mass Comparator Bangladesh BEST Programme
Mass comparators are used for comparison of precision masses. Generally the construction of these balances is similar to electromagnetic force compensation type but they are built with more precision and stability. Mass Comparators are available in capacities in the range 0.1 µg to 20 kg with excellent repeatability and linearity.

21. Bangladesh BEST Programme
Thank You