As a kind of high-accuracy mass metrology, electronic balance is widely used in school, laboratory, and factory due to excellent accuracy, fast response speed, high reliability, and easy operation. Actually, sensor, electronic, and microcomputer technology played an important role in the development of electronic balance. Electronic balance magnet is one of the representative application of cast Alnico magnet.
Basic Principle of Electronic Balance
The weighing principle of electronic balance is bases on the balance between electromagnetic force and gravity. The major components of electronic balance include power, electromagnetic force equilibrium transducer, photoelectric sensor, keyboard, display, and control circuit. The electromagnetic force equilibrium transducer in equilibrium under no-load condition. The position of moving coil will change after placed object to electronic balance, then influence light intensity which received by the photosensitive element, thereby, output current will be also changed. This variation will control the moving coil current after processed by the microprocessor. Hence equilibrium transducer will be back to the equilibrium state. Meanwhile, current change of the moving coil will translate into the digital signal by the microprocessor, and display reading rapidly. Electromagnetic force F generated by moving coil is equal to gravity:
Where m is the mass of the object; g is the acceleration of gravity; B is the magnetic induction; θ is the angle between the electrified conductor and magnetic field; L and I are the effective length and current of moving coil respectively. It should be noted that sinθ is equal to 1, that is:
Error Sources of Electronic Balance
The error sources of electronic balance comes from many aspects:
- Acceleration of gravity.
- Temperature variation of electronic balance is mainly caused by ambient temperature change and overheated overcurrent element. The electronic balance must be preheated before use, and makes electronic balance magnet reach thermal equilibrium state.
About Electronic Balance Magnet and Assembly
In order to avoid error sources caused by temperature, electronic balance magnet should be utilized low temperature coefficient magnet. Samarium cobalt magnet can serve excellent thermal stability and measurement range, but its cost price is extremely high. Cast Alnico magnet is acknowledged as the most suitable electronic balance magnet under this circumstance.
