How to choose different bolt loadcell

Inductive bolt loadcell

Electromagnetic bolt loadcell is a general term for a variety of sensors that utilize electromagnetic principles, including inductive bolt loadcells, Hall bolt loadcells, and eddy current bolt loadcells.

 

The working principle of the inductive bolt loadcell is that due to the different magnetic materials and permeability, when the bolt acts on the diaphragm, the size of the air gap changes, and the change of the air gap affects the change of the coil inductance. The processing circuit can convert the change of this inductance. into the corresponding signal output, so as to achieve the purpose of measuring bolt. This kind of bolt loadcell can be divided into two types according to the change of magnetic circuit: variable reluctance and variable permeability. The advantages of inductive bolt loadcells are high sensitivity and large measurement range; the disadvantage is that they cannot be used in high-frequency dynamic environments.

 

The main components of the variable reluctance bolt loadcell are the iron core and the diaphragm. The air gap between them forms a magnetic circuit. When there is bolt, the size of the air gap changes, that is, the magnetoresistance changes. If a certain voltage is applied to the iron core coil, the current will change with the change of the air gap, thereby measuring the bolt.

 

In the case of high magnetic flux density, the permeability of ferromagnetic materials is unstable. In this case, a variable permeability bolt loadcell can be used to measure. The variable permeability bolt loadcell replaces the iron core with a movable magnetic element. The change of bolt causes the movement of the magnetic element, so that the permeability changes, and the bolt value is obtained.

 

Hall bolt loadcell

Hall bolt loadcells are based on the Hall effect of certain semiconductor materials. The Hall effect refers to the phenomenon that when a solid conductor is placed in a magnetic field and a current passes through it, the charge carriers in the conductor are biased to one side by the Lorentz force, and then a voltage (Hall voltage) is generated. The electric force induced by the voltage balances the Lorentz force. From the polarity of the Hall voltage, it can be confirmed that the current inside the conductor is caused by the movement of negatively charged particles (free electrons).

 

Applying a magnetic field perpendicular to the current direction on the conductor will cause the electrons in the wire to be gathered by the Lorentz force, thereby generating an electric field in the direction of the electron gathering, which will cause the subsequent electrons to be balanced by the action of electricity. The Lorentz force caused by the magnetic field enables subsequent electrons to pass smoothly without being displaced, which is called the Hall effect. The resulting built-in voltage is called the Hall voltage.

 

When the magnetic field is an alternating magnetic field, the Hall electromotive force is also an alternating electromotive force of the same frequency, and the time for establishing the Hall electromotive force is extremely short, so the response frequency is high. The material of the ideal Hall element requires high resistivity and carrier mobility in order to obtain a large Hall electromotive force. The materials of the commonly used Hall elements are mostly semiconductors, including N-type silicon (Si), indium antimonide (InSb), indium arsenide (InAs), germanium (Ge), gallium arsenide (GaAs) and multilayer semiconductor structural materials, N The Hall coefficient, temperature stability and linearity of silicon-type silicon are all good, and the temperature drift of gallium arsenide is small, and it is currently used.

 

Eddy current bolt loadcell

A bolt loadcell based on the eddy current effect. Eddy current effects are produced by the intersection of a moving magnetic field with a metallic conductor, or by the perpendicular intersection of a moving metallic conductor with the magnetic field. In short, it is caused by the effect of electromagnetic induction. This action creates a current circulating in the conductor.

 

The eddy current characteristic makes the eddy current detection have the characteristics of zero frequency response, so the eddy current bolt loadcell can be used for the detection of static force.

 

Vibrating wire bolt loadcell

The vibrating wire bolt loadcell is a frequency-sensitive sensor. This frequency measurement has a high accuracy, because time and frequency are physical parameters that can be accurately measured, and the resistance, inductance, etc. of the cable can be ignored during the transmission of frequency signals. capacitance and other factors. At the same time, the vibrating wire bolt loadcell also has strong anti-interference ability, small zero drift, good temperature characteristics, simple structure, high resolution, stable performance, easy data transmission, processing and storage, and easy to realize instrument digitization, so vibrating wire Type bolt loadcell can also be used as one of the development directions of sensing technology.

 

The sensitive element of the vibrating wire bolt loadcell is a tensioned steel string, and the natural frequency of the sensitive element is related to the magnitude of the tensioning force. The length of the string is fixed, and the change of the vibration frequency of the string can be used to measure the magnitude of the pulling force, that is, the input is a force signal, and the output is a frequency signal. The vibrating wire bolt loadcell is divided into upper and lower parts, and the lower part is mainly a combination of sensitive elements. The upper part is an aluminum shell, which contains an electronic module and a terminal, which is divided into two compartments, so that the sealing of the electronic module compartment will not be affected during wiring.

 

The vibrating wire bolt loadcell can choose current output type and frequency output type. When the vibrating wire bolt loadcell is in operation, the vibrating wire vibrates continuously at its resonant frequency. When the measured bolt changes, the frequency will change. This frequency signal can be converted into a 4~20mA current signal through the converter.