Working principle of inductive sensors in balances

　　Inductive sensors are mainly used in electronic precision balances. The important feature of precision balances is that when measuring the mass of the object being measured, it does not measure the gravity of the weight, but uses the principle of balancing the electromagnetic force and the gravity of the object being measured. The scale pan is connected to the coil through the bracket connecting rod. Within the weighing range, when the gravity mg of the measured weight acts on the coil through the connecting rod bracket in an upward direction, if there is current passing through the magnetic field, the coil will generate an electromagnetic force F, which can be expressed by the following formula: F=KBLI

　　Among them, K is a constant (related to the unit used), B is the magnetic induction intensity, L is the length of the coil wire, and I is the current intensity passing through the coil wire. The electromagnetic force F and the weight of the object being measured mg on the scale pan are equal in magnitude and opposite in direction to achieve balance. At the same time, the scale pan bracket returns to its original position under the action of the elastic spring. That is, F=KBLI=mg

　　From the above formula, we can know that for a coil with current in a magnetic field, the current I flowing through it is proportional to the mass of the object being measured. As long as the current I is measured, the mass m of the object can be known.

　　In order to further improve the accuracy of any balance control system, a closed-loop control system is required. If the object being weighed increases in weight, the balance will become unbalanced. The photoelectric detector detects the transient displacement of the coil in the magnetic steel, and a variable output is generated through the preamplifier and PID regulator. It is then compared with the fixed sawtooth wave to widen the width-modulated pulse, and the width-modulated pulse is used to control the current switch to reduce the current. The constant current source is fixed, thereby increasing the current flowing through the coil, thereby increasing the electromagnetic force and offsetting it with the object being measured to achieve a new balance state.