The rack balance is a mechanical equilateral lever weighing instrument consisting of a base, a beam, two trays, a weight, a traveler and a balance adjustment part. It is characterized by simple structure, convenient operation and low cost, and is mainly used for rapid weighing of object mass, with an accuracy between the bench scale and the analytical balance, and is suitable for conventional scenarios with low requirements for measurement accuracy.
type
Divided by accuracy level
The ordinary rack plate has a large balance-index value (usually 0.1g or 0.2g), and a wide weighing range, which is suitable for teaching experiments in primary and secondary schools, simple ratio of industrial raw materials, and other scenarios.
The precision rack balance has a smaller index value (up to 0.01g) and stronger structural stability, and is mostly used for routine sample weighing in the laboratory, food processing and low-dose material ratio.
Divided by usage scenario
Teaching Rack Balances - Lightweight design, with clear scale markings and guards to facilitate students' understanding of lever principles and weighing operations.
Laboratory special rack balance - the material is stronger, the beam is rigid, and the anti-interference ability is strong, which can meet the weighing needs of basic physical and chemical experiments.
Divided by structural form
Conventional rack balance - pallet is placed directly at both ends of the beam, and it is a common type to manually add weights and move the code.
Torsion rack balance - uses torsion springs to replace part of the lever structure, which is smaller and suitable for occasions where space is limited.
Test principle
The core working principle of the rack balance is the principle of equivalence lever balance.
1. The midpoint of the balance beam is the fulcrum, and the length of the arm at both ends is equal. When unloaded, the beam is kept horizontally balanced by adjusting the balance nut.
2. When weighing, place the object to be measured on the left disk, add a weight of known mass to the right disk, and move the number code on the beam (the number code is equivalent to the small weight that can be moved).
3. When the beam reaches horizontal equilibrium again, according to the lever balance condition (left disc object mass × left arm length = right disc weight total mass × right arm length), since the force arm is equal, the object mass to be measured = total weight mass + the corresponding scale value of the travel code.
Fields of application
Teaching field in primary and secondary schools - as a basic instrument for physics and chemistry experiments, it is used to demonstrate the principle of levers, teach the basic operation of weighing, and help students establish the concept of mass measurement.
Basic laboratory field - suitable for basic experiments in universities and scientific research institutes, complete the rough preparation of reagents, preliminary weighing of samples, etc., and provide basic data for subsequent high-precision analysis.
Industrial production field - used for simple ratio of raw materials in the workshop, quality sampling inspection of parts, etc., to meet the needs of rapid weighing of production lines.
Commercial retail – some small shops are used to weigh small quantities of goods (e.g. dry goods, spices) with intuitive operation and easy understanding for customers.
Common faults and solutions
The beam cannot be balanced when not loaded
Fault cause - improper adjustment of the balance nut; Pallet placement is incorrect; the base is not level; The beam is deformed.
Solution - Readjust the balance nut to the beam level; Confirm that the left and right pallets are installed in the correct position; Adjust the base foot pad to keep the balance horizontal; If the beam is severely deformed, the parts need to be replaced.
The weighing results are inaccurate
Fault cause - quality deviation caused by rust or wear of weights; The game code has not returned to zero; The wear of the knife edge affects the balance of the lever. The balance is disturbed by external forces during weighing.
Solution - Replace rusted and worn weights; Make sure that the code moves to the zero scale before weighing; The blade edge is worn and needs to be professionally repaired; Weigh in a windless, vibration-free environment.
The beam swings inflexibly
Cause of failure - insufficient lubrication of the fulcrum (knife edge); loose beam or pallet components; There is a blockage of debris in the balance.
Solution - apply a small amount of special lubricant to the knife edge; fastening loose screws and components; Clean the inside of the balance from dust and debris.
How to choose
1. Clarify precision and range requirements
Teaching or coarse preparation reagent: choose the ordinary type with an index value of 0.1g~0.2g and a measurement range of 100g~1000g.
Laboratory routine weighing: choose the precision type with a index value of 0.01g and a measuring range of 200g~500g.
2. Match usage scenarios
Classroom teaching: Priority should be given to lightweight and protective teaching models, which are convenient for handling and demonstration.
Industrial workshops: Choose conventional models with strong materials and strong anti-interference capabilities to adapt to complex environments.
3. Focus on the quality of core components
Preferentially choose models made of high-quality alloy and hard wear-resistant materials at the edge of the knife to extend the service life.
Check whether the weights are matched and whether the scales are clear to avoid affecting the use due to missing accessories.
4. Consider additional features
Choose a model with a windscreen (for airflow) or a pallet guard (to prevent material spillage) as required.
summary
The rack balance is a basic weighing instrument based on the principle of equal arm lever, which has the characteristics of simple structure, convenient operation and low cost, and is widely used in teaching, basic experiments, industrial ratio and other scenarios. The selection should be combined with accuracy, range and use environment, and timely troubleshoot faults such as abnormal balance and inaccurate weighing in daily use, which can ensure its stable operation and meet the needs of conventional weighing.
