I. Introduction: A calibrator for an electromagnetic flowmeter signal converter is a device used for performance testing and calibration of electromagnetic flowmeter signal converters. Existing electromagnetic flowmeter signal converters consist of a series of high-precision resistor networks, generally allowing only fixed-point testing and calibration. Different manufacturers' converters have different amplification factors and other parameters. Therefore, such calibrators can only perform fixed-point testing and calibration of specific electromagnetic flowmeter signal converters under unmonitored conditions, limiting the application of electromagnetic flowmeters. II. Design Concept: The designed calibrator for an electromagnetic flowmeter signal converter includes an external electromagnetic flowmeter signal converter to be calibrated and a resistor network that outputs a simulated fluid velocity signal to be measured by the electromagnetic flowmeter. The excitation current output by the electromagnetic flowmeter signal converter provides power and a synchronization signal, resulting in an analog output signal from the electromagnetic flowmeter sensor. The relative magnitude of this analog signal can be steplessly adjusted and measured; furthermore, the output signal can be adjusted according to different types of converters, simulating different flow velocity signals and different fluid impedances. The relative amplitude of the output signal can be measured with a common digital voltmeter, and it can be used to calibrate electromagnetic flowmeter signal converters from different manufacturers. Three implementation schemes: This design includes an external electromagnetic flowmeter signal converter to be calibrated and a resistor network that outputs a simulated fluid velocity signal to be measured by the electromagnetic flowmeter. The excitation current output of the external electromagnetic flowmeter signal converter is connected to the primary input of a transformer via a bidirectional voltage regulator. The secondary output of the transformer is connected to the input of the resistor network. The output of the resistor network is rectified by a full-wave rectifier and then connected to the input of a freewheeling circuit and a constant current source circuit. The output of the constant current source circuit is connected to a sampling resistor. The resistor network simultaneously outputs the simulated fluid velocity signal to be measured by the electromagnetic flowmeter, which is connected to the signal input of the external electromagnetic flowmeter signal converter. Four calibrator circuit implementation process: The circuit schematic is shown in Figure 2. 1) The two output terminals of the electromagnetic flowmeter excitation current S1 are connected in parallel with the two ends of the bidirectional voltage regulator circuit and the two input terminals of the primary coil of the transformer, respectively. The output of the secondary coil of the transformer is a signal synchronization source and a working power supply S2 that are electrically isolated from S1. 2) The two output terminals of the transformer secondary coil output signal S2 are connected to the input terminal of the resistor network and the AC input terminal of the full-wave rectifier, respectively. The DC output terminal of the full-wave rectifier provides power to the load circuit formed by the series connection of the adjustable constant current source and the sampling resistor. The anode of the full-wave rectifier is connected to the input of the adjustable constant current source and one end of the freewheeling circuit, the cathode of the full-wave rectifier is connected to the other end of the freewheeling circuit, and the other end of the sampling resistor is connected to the output of the constant current source circuit. When the switch SW1 of the freewheeling circuit is open, the current I value A determined by the adjustable constant current source determines the positive and negative amplitude A of the alternating current I flowing through the input terminal of the resistor network, so that the output signal S3 of the resistor network output verifier has positive and negative amplitude B; B=KХA, where K is the attenuation coefficient, determined by the resistance value in the resistor network; 3) The freewheeling circuit composed of capacitor and switch SW1 is connected in parallel to the DC output terminal of the full-wave rectifier. When the switch SW1 of the freewheeling circuit is closed, the current I value A determined by the adjustable constant current source forms a directly measurable DC voltage signal S4 on the sampling resistor. The positive and negative amplitude A of the alternating current I of signal S3 can be obtained through signal S4, where A=S4/R, and R is the resistance value of the sampling resistor. 4) When the switch SW1 of the freewheeling circuit is open, the output signal S3 of the calibrator is determined by the adjustable constant current source current i value A. Then, when the switch SW1 of the freewheeling circuit is closed, the positive and negative amplitude B of the actual calibrator output signal S3 is obtained by measuring the signal S4: B = K×S4/R. The current waveforms of each part during operation are shown in Figure 3. The output of the full-wave rectifier circuit D2 provides power to U1, which is an adjustable constant current source circuit. In this example, LM334 is selected. The current can be adjusted by adjusting R4. The magnitude of the current can be obtained by measuring the voltage across R6. When measuring the voltage across this voltage with a common voltmeter, switch SW1 should be turned on. Capacitor C1 is connected to the circuit to act as a filter, so that the current source circuit receives a stable power input, thereby obtaining a stable and accurately measurable voltage across R6. After the measurement is completed, SW1 should be turned off. In the circuit shown in Figure 2, by adjusting the constant current source, the obtained current ranges from 2 microamps to 4 milliamps. The output voltage range at S3 is approximately 0 millivolts to 40 millivolts. Correspondingly, the voltage across the measuring resistor R6 is approximately 200 microvolts to 400 millivolts, which can be measured using a standard digital voltmeter. Adjusting R3 and R4 allows this device to be compatible with electromagnetic flowmeter converters from different manufacturers. The current waveforms of each part of the designed electromagnetic flowmeter signal converter calibrator are shown in Figure 3. V. Measurement Circuit Based on the Calibrator Using chips such as the PIC18LF2520, the voltage signal across resistor R6 and the square wave signal at S3 can be measured. This allows the acquisition of the regulating voltage value and flow rate signal value. Its circuit block diagram is shown in Figure 4. The hardware design of the circuit mainly includes signal conditioning, A/D conversion, LCD display, and peripheral circuits related to the microcontroller. The voltage signal obtained from the electromagnetic flow sensor is processed by the signal conditioning circuit, then converted from analog to digital by an A/D converter, and finally processed numerically by the CPU. The corresponding flow rate is displayed on an LCD screen. The main functions of each module are as follows: Sensor signal acquisition and signal conditioning circuit: The core and challenge lies in controlling the polarization voltage to a repeatable and stable value, extracting the weak induced electromotive force, and adjusting it to an appropriate range that subsequent circuits can handle. Due to the adoption of automatic tracking feedback control, the signal conditioning circuit is controlled by a microcontroller. A/D conversion circuit: To ensure measurement accuracy and stability, a 16-bit Σ-Δ type analog-to-digital converter is used, which has high measurement accuracy and strong anti-interference ability. Microcontroller-related peripheral circuits: Clock, reset circuit, keyboard, and LCD display. The keyboard input records the initial zero point, and the LCD displays the flow rate in real time. Power supply: The power supply of the entire flow measurement system uses a high-energy-density lithium battery. The main program flowchart of the electromagnetic flowmeter software design based on this calibrator is shown in Figure 5 . Conclusion Compared with the existing technology, this design has the following obvious outstanding features and significant advantages: the excitation current is used to provide power for the circuit operation, eliminating the need for batteries required by the usual analog signal generator; the output signal obtained by using the output resistor network and constant current circuit in series is strictly symmetrical and can simulate the state of fluid flowing at a constant speed in the pipe; the output signal is synchronized with the excitation signal, the signal size can be steplessly adjusted and the relative size can be measured, which can be adapted to converters from different manufacturers, and is particularly suitable for performance verification in the production process of electromagnetic flowmeter signal converters. The electromagnetic flowmeter designed based on this calibrator has been proven to be effective in practice. The measurement accuracy has been greatly improved. References: [1] Li Bin; Bao Haiyan. [1] Discussion on signal processing method of electromagnetic flowmeter [J] Journal of Shanghai University of Science and Technology, 1998.2 241-245 [2] Cao Jinliang; Li Bin Research on empty pipe detection method of electromagnetic flowmeter [J] Journal of Instrumentation 2006.6 643-647 [3] Guo Yueguang; Liu Yanyan Research on empty pipe detection method of electromagnetic flowmeter [J] Urban Water Supply 2006.2 35, 21 [4] Su Xing; Wang Baoliang Development of intelligent electromagnetic flowmeter converter based on ARM [J] Mechanical and Electrical Engineering 2006.3 23-25 ​​[5] Cai Wuchang; Ma Zhongyuan; Qu Guofang; et al. Electromagnetic Flowmeter [M] Beijing: China Petrochemical Press, 2004 [6] Sun Xiangdong; He Xiaoqin; Intelligent front-end signal circuit design of electromagnetic flowmeter [J] Single-chip Microcomputer and Embedded System Application 2002.7 66-68 Editor: He Shiping