Abstract: This paper introduces the characteristic parameters and working principle of the JN338 intelligent digital torque and speed sensor. This sensor uses two sets of rotary transformers to achieve non-contact power and signal transmission, and its signal output is a frequency quantity. The paper presents the hardware circuit block diagram of an intelligent torque and speed measuring instrument based on the JN338, and points out the application precautions for the JN338. Keywords: JN338; digital; torque and speed sensor 1. Overview Torque sensors have been widely used in numerous rotating power testing systems such as electric motors, engines, generators, fans, mixers, winches, and drilling machinery, as well as in mechatronic equipment such as CNC machining centers and automatic machine tools. Traditional torque sensors typically use resistance strain gauge bridges to detect torque signals and conductive slip rings to couple the power input and strain signal output. Since the conductive slip ring is a friction contact, wear and heat generation are inevitable. This not only limits the rotational speed of the rotating shaft and the service life of the conductive slip ring, but also inevitably causes fluctuations in the measurement signal and increases in error due to unreliable contact. Therefore, reliably coupling energy and signals on a rotating shaft has become the most challenging problem for torque sensors, and the JN338 digital torque-speed sensor cleverly solves this problem. The JN338 is a product of Beijing Sanjing Venture Group Co., Ltd. This sensor uses two sets of special toroidal rotary transformers to achieve energy input and torque signal output, thus solving the problem of reliable energy and signal transmission between rotating and stationary parts in a rotating power transmission system. This sensor can also simultaneously measure the rotational speed of the shaft, allowing for convenient calculation of the shaft output power. Therefore, this sensor can be used to achieve multi-parameter output of torque, speed, and shaft power. 2. Main Characteristics and Parameters 2.1 Main Characteristics of JN338 The main characteristics of JN338 are as follows: ● Detection method is strain gauge electrical measurement technology; ● High measurement accuracy; signal detection and processing both use digital technology; ● Strong anti-interference ability; can work without zeroing; ● High reliability, high signal-to-noise ratio, and long service life; ● Can measure both static torque and rotating torque; ● Can measure steady-state torque and dynamic torque during transient processes; ● Can continuously measure positive and negative torque without repeated zeroing; ● No wear parts such as slip rings and brushes; can operate at high speed and for extended periods; ● Torque signal transmission is independent of rotation, speed, and direction; ● Measured elastic body has high strength and can withstand 150% overload; ● Small size, light weight, and easy installation; available in various installation methods such as kit type, clip type, and coupling type; ● Output signal is given in frequency form, facilitating interface with computers. 2.2 Main Technical Parameters of the Sensor The main technical parameters of the sensor are shown in Table 1. Table 1: Main Technical Parameters of JN338 Sensor Torque Accuracy >0.5% Overload Capacity 150%FS Insulation Resistance ≥200MΩ Operating Temperature -20～60℃ Repeatability ≤0.5%FS Hysteresis ≤0.5%FS Linearity ≤0.5%FS Relative Humidity ≤90%RH 2.3 Socket Pins and Functions The JN338 torque-speed sensor uses a 5-pin aviation socket for power input and torque-speed signal output. The socket shape and pin arrangement are shown in Figure 1. The functions of each pin are as follows: Pin 1: Ground terminal; Pin 2: +15V power supply terminal; Pin 3: -15V power supply terminal; Pin 4: Speed ​​signal output terminal; Pin 5: Torque signal output terminal. 3 Working Principle 3.1 Torque Measurement Principle The sensing element of this torque sensor is a resistance strain gauge bridge. A specialized torsion strain gauge is attached to the elastic shaft being measured using strain adhesive to form a strain bridge. By supplying power to the strain bridge, the electrical signal of the elastic shaft under torsion can be measured. This strain signal is then amplified and converted into a frequency signal proportional to the torsional strain through a voltage-to-frequency converter. The energy input and signal output of the sensor are handled by two sets of special toroidal rotary transformers with gaps, thus enabling contactless energy and signal transmission. The measurement principle of this strain sensor is shown in Figure 2. A specialized torsion strain gauge is attached to a specially designed elastic shaft to form a bridge, forming the basic torque sensor. Then, the secondary coil of the energy toroidal rotary transformer, the printed circuit board on the shaft, and the primary coil of the signal toroidal rotary transformer are fixed to the shaft. The circuit board includes a rectified and regulated power supply, an instrumentation amplifier circuit, and a V/F conversion circuit. The excitation circuit, the primary coil of the energy toroidal rotary transformer, the secondary coil of the signal toroidal transformer, and the signal processing circuit are fixed to the sensor housing. During operation, the sensor circuit receives ±15V power from an external power source. The crystal oscillator in the excitation circuit generates a 400Hz square wave, which is amplified by a TDA2003 power amplifier to produce AC excitation power. This AC power is then transferred from the stationary primary coil T1 to the rotating secondary coil T2 via a toroidal rotary transformer. The resulting AC power is then rectified and filtered by an on-shaft rectifier and filter circuit to become ±5V DC power. This power supply is then used as the operating power for the operational amplifier AD822. A high-precision regulated power supply, consisting of a reference power supply AD589 and the dual operational amplifier AD822, generates a precision ±4.5V DC power supply. This power supply can be used as a strain gauge bridge power supply, as well as the operating power for the instrumentation amplifier and V/F converter. When the elastic shaft is subjected to torsion, the strain signal at the mV level detected by the strain bridge is amplified into a strong signal of 1.5V±1V by the instrumentation amplifier AD620, and then converted into a frequency signal by the V/F converter LM331. This signal is transmitted from the rotating shaft to the stationary secondary coil through the signal ring rotary transformer, and then filtered and shaped by the signal processing circuit on the sensor housing to obtain a frequency signal output proportional to the torque on the elastic bearing. 3.2 Speed ​​Measurement Principle The torque sensor has a speed measuring wheel with 60 teeth mounted on the rotating shaft. A slotted photoelectric switch frame composed of light-emitting diodes and phototransistors is mounted on the sensor housing. When each tooth of the speed measuring wheel blocks the light from the light-emitting diode, the phototransistor outputs a high level. When the light passes through the teeth and shines into the window of the phototransistor, the phototransistor outputs a low level. 60 pulses are obtained for each rotation of the rotating shaft. Therefore, the number of pulses detected per second is exactly equal to the speed value per minute. 3.3 Shaft Output Power The shaft output power can be obtained by calculating the torque and speed values ​​output by the torque sensor. The calculation formula is: p = MN / 9550 Where, P is the shaft output power (kW); M is the torque (N·m); N is the speed (r/min). 3.4 Torque Sensor Signal Output The JN338 torque sensor signal output forms are as follows: ● Zero torque: 10 kHz ± 50 Hz; ● Full-scale forward rotation: 15 kHz ± 50 Hz; ● Full-scale reverse rotation: 5 kHz ± 50 Hz; ● Signal amplitude: 0~8V; Load current: 40 mA. Within the effective range, the sensor's torque frequency output is basically linearly related to the corresponding torque value. In practical applications, if the measurement accuracy requirement does not exceed the nominal value, it is generally not necessary to complete the calculation through segmented parameter calibration. ● Torque Output The torque measurement calculation formulas are given below: Forward torque output value: Mp = N(f - f0) / (fp - f0) Reverse torque output value: Mr = N(f0 - f) / (f0 - fr) Where: Mp: forward torque; Mr: reverse torque; N: torque full scale; fp: forward full scale output frequency value (kHz); fr: reverse full scale output frequency value (kHz); f: measured torque output frequency value. ● Speed ​​Output The speed output value of this device is: N = 60f / z Where, N is the speed (r/min); f is the measured speed output frequency value (kHz); Z is the number of teeth on the sensor, here Z is 60. The corresponding curves of torque value and output frequency value are shown in Figure 3. 4. Specific Applications 4.1 Application Circuit Design Since the output of the JN338 is a digital signal representing frequency, this sensor can be easily interfaced with a computer or microcontroller. Interface with a computer requires an expansion of a multi-channel timer/counter board based on the ISA bus or PCI bus, such as the "Zhongtai" optically isolated timer/counter board PC-6503 or PC-6508. Figure 4 shows the hardware circuit structure block diagram of the intelligent torque and speed measuring instrument configured with a microcontroller interface. In the figure, the torque and speed signals output by the JN338 torque sensor are optically isolated and then sent to the T0 and T1 counters of the microcontroller. T0 and T1 then perform the frequency measurement and counting function, while the second pulse gate is provided by T2. The role of the optical coupler is twofold: first, level conversion, converting the torque and speed signal level to TTL level; second, improving the microcontroller's anti-interference capability and protecting the microcontroller. After the microcontroller completes the calculation of the corresponding torque and speed values, it can save and display the parameters such as torque, speed, and shaft power. This system uses the AT89C52 microcontroller as its core and employs an IMP813L to construct power monitoring and watchdog circuits to improve system reliability. An I2C bus serial ferroelectric memory FM24256 is added to the system; its main function is to store parameter settings and acquired torque and speed values. An OCMJ4X8C graphic dot-matrix LCD module with a built-in GB2312 Chinese character library can be used to construct a Chinese human-machine interface. The ICL232 converts the microcontroller's TTL level to RS-232 level for communication with the host computer. 4.2 Installation and Usage Precautions When installing and using the JN338 sensor, the following points should be noted: (1) Two sets of couplings should be used to install the sensor between the power source and the load; (2) It is recommended to use flexible, elastic, or directional couplings to ensure that the concentricity is less than 0.1; (3) The power source and load must be firmly fixed to avoid vibration; (4) The base of the sensor should be firmly fixed to the base of the equipment, the center height should be adjusted appropriately, and additional torque should be avoided. 5 Conclusion The JN338 digital torque and speed sensor is a new type of torque and speed sensor that uses magnetic field coupling to transmit energy and signals. This sensor eliminates the slip ring structure of the traditional torque sensor and adopts digital output, thus having the characteristics of small size, light weight, simple and convenient installation, and simple and convenient microcomputer measurement interface. It is a torque and speed sensor with broad development prospects.