Workers engaged in weighing instruments often have a good understanding of the weights used to calibrate weighing instruments
Not paying much attention to it, and perhaps even less familiar with the prototype of the kilogram. Here
Introducing knowledge about the kilogram prototype is of great significance to weighing instrument workers
Righteous.
The prototype of the International kilogram has a diameter of 39mm, a height of 39mm, and contains platinum
A 90% platinum-iridium alloy cylinder containing 10% iridium has a density of approximately
21.5g/cm ³. It was first defined by the General Conference on Weights and Measures in 1889 as
The International prototype of the kilogram has been kept in Paris since its time
Sevres International Bureau of Weights and Measures (abbreviated as BIPM).
There is a fundamental difference between quality and other basic quantities, and
The current definitions of the unit of length, the meter, and the unit of time, the second, are inconsistent
In this way, it cannot be traced back to a natural constant but uses one
It can be defined by specific physical objects. So its quantity value (that is, its magnitude) can only pass through
It is determined by the value of the "force" it experiences. In a sense, the so-called
The definition of "force" is an abstract physical concept and cannot be like length
(meters) and time (seconds) are concrete to our senses
Feeling. Even up to now, the value of "mass" is measured through electricity
A method is associated with the fundamental amount of a substance. And this basic
Quantities and the inertial mass and gravitational mass that we are accustomed to using in mechanics (citation)
The definition of "force-mass" is not direct from the perspective of physical concepts
The relationship. It is not like the transitions in quantum mechanics that characterize frequency (time) and
The definition of wavelength (length) is the same and has a physical connection. So the quality
The so-called "natural benchmark" only addresses the quantity of the past physical benchmark
The uncertainty and unknowability of value changes.
The prototype of China's national kilogram was introduced from the United Kingdom in 1965
At that time, China had not yet joined the International Organization of Legal Metrology.
The number of China's national kilogram prototype is No.60.
Mass: M (No.60) =1kg+0.27/mg±0.08mg
Volume: V (0℃) =46.3867cm ³
Coefficient of expansion: α= (25.863+0.00562t) X-6/℃
Volume: V (20℃) = 46.4108cm ³
This prototype was officially approved as a national quality standard in 1986. each
The national prototype of the country is matched with the BIPM international kilogram prototype through the prototype balance
In connection with it and in accordance with the requirements of BIPM, send it to BIMP for processing
Comparison. The first international comparison (from 1899 to 1901)
It took nearly two years to complete. For the original equipment of 18 countries, four have not yet been developed
The allocated prototypes, two working prototypes of the International Bureau of Weights and Measures, and the country
The two earlier working prototypes of the International Bureau of Weights and Measures, C and S (C is a cylinder),
S is the truncated ball body, and it is compared with the International Kilogram Verification Benchmark Prototype No.1
Comparison.
By comparison, the quality changes of those unused primitives are
It is allowed within the microgram range, while the working principle No.31 of the International Bureau of Weights and Measures
Due to frequent use, its mass has decreased by 20μg.
The second international comparison was conducted between 1948 and 1935.
A total of 33 prototypes participated in the comparison. The third international comparison was conducted in 1987
From 1993 to 1993, a total of 39 original objects participated in the comparison. "China"
National Kilogram Prototype No.64 participated in this comparison, China
The comparison results of Prototype No.64 are as follows:
M (No. 64) = + 0.251 mg + / - 0.0023 mg/kg
two
Weights serve as a carrier to represent the magnitude of "mass", and their essence
The body cannot be used as an instrument for measuring the mass of an object. Measuring an object
Mass is determined by comparing the object under test with the weights of the mass carrier
As a result, under the effect of gravity, a comparison device is used to confirm the comparison
1
Since the force and moment acting on an object are equal, this comparison device is
It is called a "weighing instrument" (or balance).
The result measured by weighing instruments as an approximate value of mass is called
Measurement value.
When an object is in a medium (such as air or other media), except
Due to the effect of gravity, according to Archimedes' principle, it is also subject to the buoyancy of the medium
The action of force.
When the density of the object being measured is different from that of the weight, the comparative force is balanced
The equilibrium equation in the presence of a medium is
mm
·g1
L1 - rho, 1
·Vm
·g1
·l1
=mp
·g2
L2 - rho, 2
·Vp
·g2
·l2
In the formula: ρ1
And ρ2
-- The density of the weights and the object being weighed;
g1
And g2
The gravitational acceleration at the position where the weights and the object being weighed are located
Degree;
l1
And l2
-- The torque of the force exerted by an object;
Vm
And Vp
-- The volume of the weights and the object being weighed;
mm
And mp
The "true" mass of the weights and the object being weighed.
Under normal circumstances, it can be regarded as g1
=g2
l1
=l2
And there are two things
The mass is all in (ρ0
Rho = 1
Rho = 2
If the weight is carried out in the air, then
There are:
mp
=mm
+ rho 0
(Vp-Vm
)
Units of measurement when people usually measure the mass of an object with weighing instruments
It can be raised from the "gram" level to the "ton" level, so it is necessary
There are various weights of corresponding weight and accuracy grades to transfer the quantity of mass
Value, that is, using weights to calibrate weighing instruments.
The weights used for weighing nowadays are basically made of stainless steel
There is a significant difference in density between steel and the object being weighed. That is
The volumes of objects of the same weight can vary greatly. As is well known,
It is not necessary only when the volume of the object being weighed is equal to that of the weight
The influence of air buoyancy should be taken into account.
The values of the weighing instruments mentioned earlier actually refer to those without taking air into account
The mass value of an object weighed by a calibrated weighing instrument with weights when buoyancy occurs.
From this, it can be seen that the measured value of an object depends on the air density and the object being weighed
The volume. In trade, when the tolerance △m/m is less than 10-3, it is considered realistic
For practical reasons, we assume that the value of a weighing instrument is the mass of an object. Therefore
In trade, the maximum allowable error of Grade III and Grade IV scales should be stipulated at
Within this error range.
The density of the international prototype of the kilogram is approximately 21.5g/cm ³, and its mass
When the quantity value is transferred to the working weight (i.e., the reference weight), people must
It is necessary to know the exact density or volume of the weights, as well as the exact air density
Degree. Therefore, the entire measurement operation process is extremely complicated
Work.
In order to simplify the measurement work of quality comparison, legal metrology is adopted
In this context, if we have specified the density of the weights and within the prescribed standards
Mass comparison under air density can enable the measurement of mass comparison
The uncertainty in work is very small and it is easy to operate, so it is measured in this way
The quality value is called the fixed quantity value.
Since this new verification method was established in 1975, weights
The standard value is no longer its own mass, but a reference weight (for work)
The mass of the weights. The density of the reference weight is 8000kg/m ³ in the empty space
At a density of 1.2kg/m ³ in the air and a temperature of 20℃, it is comparable to the original weight
Maintaining balance, such an agreed measurement value is the quality value.
Such a regulation holds that the weight of all objects being weighed is equal to
The agreed air density is ρ0
=1.2kg/m ³, the agreed density of the object to be weighed
It is ρk
The weight of the object under the condition of 8000kg/m ³. When being weighed, the density of things
The indication and calibration of weighing instruments when the temperature and air density do not equal the agreed values
The nominal values of the weights are inconsistent. The measurement results and the "truth" of the object
The error generated between the values is △m, which is the relative error compared with the standard value of the weight
For:
△m/mk
= (ρL-ρ0
(1/ρ-1/ρk
)
In the formula: △m - in order to make an object in air with a density of, it can
The mass that needs to be added to balance with the reference weight;
mL
-- The nominal value of the weight (the calibrated value of the weighing instrument);
Rho L
- Measure the density of space-time air;
ρ - the density of an object;
Rho k
=8000kg/m ³ - Agreed density of the reference weight;
Rho 0
=1.2kg/m ³ - Agreed air density.
The advantage of using agreed quality values lies in the fact that all nominal values are the same
For weights, regardless of their density, in an empty space with a density of 1.2kg/m ³
The forces acting in the air are the same as those of other reference weights. But when
When the air density at the measurement site deviates from 1.2kg/m ³, due to the density of the two
Different degrees result in different air buoyancy forces they experience. The weighing values of the two
The difference is △m.
However, if the density of the weights and the measurement site are appropriately selected
Air density (i.e., ρ and ρL.
The value can always cause the relative error of the weights
Difference: △m/mk
This method does not exceed the specified value when using weights
It is very beneficial to transfer the value of mass.
In legal metrology work, the allowable densities of weights are as follows
Regulation: The density of the weights must be guaranteed when the air density deviates from 1.2kg/m ³
At that time, the resulting error is at most 0.25 times the maximum allowable (that is, the error)
One quarter. Internationally, the air density deviates from the prescribed limit of 1.2kg/m ³
2
It is limited to within 10%, and this value is usually when the indoor air density deviates from the average
The average value is 1.2kg/m ³, approximately ±10%. So, "as long as the air is dense.
The accuracy should be maintained within the above-mentioned specified range, even for the highest precision level
For other weights, there is no need to consider correcting the buoyancy of the air.
When calibrating weighing instruments with weights, the absolute value of the allowable deviation of the weights is not
It should be greater than one third of the allowable deviation of the weighing instrument. It is used as a standard when transmitting quantity values
The weights should be at least one accuracy grade higher. For example, for inspection
Test F1
For high-precision weights, at least E2 should be used
Use grade weights as the standard.
However, under normal environmental factor conditions, due to environmental factors and causes
Due to the influence of user factors, the error of the measurement result can be attributed to the verification of weighing instruments
Two to three times the value or the graduation value.
As the three fundamental physical quantities in classical physics: time and length
One of the definitions of quality is "quality", which is determined by time and length
The meanings are all different. Time and length are very intuitive quantities, while quality is only
It can only be expressed through "force" or "energy - kinetic or potential energy"
"Zhi" is an abstract physical term (or concept). We don't
The value of its quantity can only be directly perceived through the senses of gravity and inertia
Measure its value by force. And so far, gravity and inertia
Whether the essence of sexual force is the same thing in terms of physical substance also exists
It awaits in-depth discussion by people.
Nowadays, although the quantity value of mass is also equivalent to it through electrical methods
On the parameters of a substance itself, there is what is called a "natural basis"
"Accurate", but its actual function is only to transform the fundamental physical aspect of "mass"
The quantity value is saved in a person using the "mass" value of the International prototype kilogram
Among the material parameters that are considered "constant and unchanging". The result is merely a solution
The difficulty of not being able to judge the changes in the original quality "physical standard" quantity value
However, the physical constant of the substance parameter cannot be used to replace the definition of "mass"
And the concept, while time and length can be replaced by physical "leaps"
Replace the original physical concepts of time and length.
In conclusion, the physical quantity of mass still needs to be transmitted through weights
The measured value is expressed and measured by using weighing instruments based on the principle of balance between force and moment
Measure the mass of an object, but the definition of mass has not changed as a result
Change. I believe that only a deep understanding of the nature of universal gravitation or gravitational intensity can lead to success
Only through understanding can one have an insight into the essence of quality.