Characteristics and Working Principle of Torque Sensors

Characteristics and Working Principle of Torque Sensors

Torque sensors have quickly become an essential component in various industries, establishing themselves as an indispensable part of the sensor family.

I. Characteristics of Torque Sensors:

1. Measurement Capability: They can measure both static and dynamic torque, as well as both stationary and rotational torque.

2. High Accuracy and Stability: They offer high detection accuracy and good stability, and are designed to prevent interference.

3. Compact and Lightweight: These sensors are small in size, lightweight, and come in various installation structures, making them easy to install and use. They can continuously measure positive and negative torque without the need for resetting to zero.

4. Durability: With no wear parts like conductive rings, they can operate at high speeds for extended periods.

5. Direct Signal Output: The sensors output high-level frequency signals that can be directly processed by computers.

6. High Overload Capacity: The elastic element used in these sensors can withstand very high overloads.

II. Measurement Principle of Torque Sensors:

Special torsional strain gauges are attached to the elastic shaft being measured, forming a strain bridge. When power is supplied to this bridge, it can measure the torsional electrical signal of the elastic shaft. This deformation signal is amplified and converted into a frequency signal proportional to the torsional reaction through a pressure/frequency conversion. Energy input and signal output for this system are managed by two sets of special ring-shaped transformers that facilitate contactless energy and signal transmission.

III. Structural Principle of Torque Sensors:

A basic torque sensor is formed by attaching special torsion measuring strips to a special elastic shaft, creating a variable electrical bridge. The following components are fixed to the shaft:

1. The secondary coil of the energy ring transformer,

2. The primary coil of the signal ring transformer,

3. A printed circuit board on the shaft, which includes rectification and stabilization power supply, instrumentation amplification circuit, V/F (voltage-to-frequency) conversion circuit, and signal output circuit.

IV. Working Process of Torque Sensors:

A 15V power supply is provided to the sensor. A crystal oscillator in the magnetic circuit generates a 400Hz square wave, which is amplified by the TDA2030 power amplifier to produce an AC magnetic power supply. This power is transmitted from the stationary primary coil to the rotating secondary coil through the energy ring transformer T1. The resulting AC power is rectified and filtered by the circuit on the shaft to obtain a 5V DC power supply, which powers the operational amplifier AD822. A high-precision 4.5V DC power supply, produced by the reference power source AD589 and dual operational amplifier AD822, is used to power the bridge, amplifier, and V/F converter.

When the elastic shaft undergoes torsion, the mV-level deformation signal detected by the strain bridge is amplified to a strong signal of 1.5V to 1V by the instrumentation amplifier AD620. This signal is then converted into a frequency signal by the V/F converter LM131. The frequency signal is transmitted from the rotating primary coil to the stationary secondary coil via the signal ring transformer T2. After filtering and shaping by the signal processing circuit in the sensor housing, the frequency signal, which is proportional to the torque applied to the elastic shaft, is obtained. Since there is only a small gap of a few millimeters between the moving and static rings, and part of the sensor shaft is enclosed in a metal housing, effective shielding is achieved, resulting in strong anti-interference capability.