Portable 4-20mA calibration device and calibration method
The portable 4-20mA calibration device solves the problem of inaccurate output from smart instruments and smart electrodes, realizing an efficient and convenient calibration method that is suitable for various environments and meets the needs of real-time detection and calibration.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-27
- Publication Date
- 2026-04-03
AI Technical Summary
The 4-20mA output of existing smart instruments and smart electrodes is prone to deviation during production, storage and use, resulting in inaccurate output. A convenient and efficient calibration method is needed to improve accuracy.
A portable 4-20mA calibration device was designed, including a housing, a touch screen, a control system, and multiple connecting cables. It achieves portable calibration through a signal acquisition circuit module and a power supply circuit module, is suitable for harsh environments, and supports real-time detection and calibration.
It improves calibration efficiency, reduces labor costs, supports real-time detection and calibration of inventory and field instruments, adapts to various environments, is easy to operate, and provides good calibration results.
Smart Images
Figure CN121783230A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of signal calibration technology, specifically relating to a portable 4-20mA calibration device and calibration method. Background Technology
[0002] The smart meter and smart electrode have a 4-20mA output. After the meter is manufactured, due to deviations in the circuit components, the 4-20mA output is not very accurate and will have a deviation. It is necessary to perform production calibration on the 4-20mA to make the output more accurate. At the same time, if the meter and electrode are stored for too long after production calibration, the 4-20mA will also deviate and the output will be inaccurate. If the electrode and meter are used at the customer's site for a long time, the 4-20mA will also deviate and the output will be inaccurate. Summary of the Invention
[0003] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a portable 4-20mA calibration device and calibration method. The device is easy to operate, improves efficiency, reduces labor costs and time, and is easy to carry. For inventory meters or electrodes that have been stored for a long time, it can detect and troubleshoot meters or electrodes with inaccurate 4-20mA output in real time, and calibrate them in real time. For instruments at the customer's site, it can also detect and calibrate them in real time. The calibration device can meet the requirements of relatively harsh environments, has good performance, and is easy to promote and use.
[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a portable 4-20mA calibration device, comprising a device body and a control system. The device body includes a housing, the control system is installed inside the housing, a touch screen is provided on the top of the housing, and multiple connecting wires are provided on the side of the housing. The control system includes a controller and a power supply circuit module for powering the control system. The input terminal of the controller is connected to a signal acquisition circuit module, and the touch screen is connected to the controller.
[0005] The aforementioned portable 4-20mA calibration device includes multiple connecting cables, comprising two signal cables, two data cables, and one power cable.
[0006] The portable 4-20mA calibration device described above has two signal lines, RS485-1 and RS485-2. RS485-1 is used to communicate with the instrument under test or the electrode; RS485-2 is used to communicate with the touch screen and the current measuring device.
[0007] The aforementioned portable 4-20mA calibration device has a human-machine interface on its touchscreen. The human-machine interface includes a parameter setting module, a button module, an indicator light module, a parameter display module, and an information prompt module. Control commands are sent to the controller through the parameter setting module and the button module, and the device status returned by the controller is displayed through the indicator light module, the parameter display module, and the information prompt module.
[0008] The aforementioned portable 4-20mA calibration device includes a power circuit module comprising a power interface J1, a DC-DC power chip U1, a DC-DC boost chip U3, an LDO buck chip U4, a lithium battery BT1, non-polar capacitors C1, C2, and C3, and a button K1. The input terminal of the DC-DC power chip U1 is connected to pin 1 of the power interface J1 and grounded through the non-polar capacitor C1. Pins 2 and 3 of the power interface J1 are both grounded. The lithium battery BT1... The positive terminal of the battery BT1, one end of the non-polar capacitor C2, and one end of the button K1 are all connected to the output terminal of the DC-DC power chip U1. The negative terminal of the lithium battery BT1 and the other end of the non-polar capacitor C2 are both grounded. The other end of the button K1 is connected to the input terminal of the DC-DC boost chip U3 and the input terminal of the LDO buck chip U4, and is grounded through the non-polar capacitor C3. The output terminal of the DC-DC boost chip U3 powers the touch screen, and the output terminal of the LDO buck chip U4 powers the acquisition circuit module.
[0009] The aforementioned portable 4-20mA calibration device includes an operational amplifier U5, an ADC acquisition chip U6, resistors R1, R2, R3, R4, R5, R6, and a non-polarized capacitor C4. The fourth pin of the operational amplifier U5 is connected to the negative terminal of the 4-20mA output of the instrument under test (DUT) or electrode via resistor R2, and is also connected to one end of resistor R1. The third pin of the operational amplifier U5 is connected to the positive terminal of the 4-20mA output of the DUT or electrode via resistor R4, and is also connected to one end of resistor R1. The other end of R1 and one end of resistor R5 are both connected. The 5th pin of operational amplifier U5 and the other end of resistor R5 are both connected. The 2nd pin of operational amplifier U5 is connected to VCC_3.3V voltage. The 1st pin of operational amplifier U5 is connected to one end of resistor R6 and is connected to the 4th pin of operational amplifier U5 through resistor R3. The other end of resistor R6 is connected to the input terminal of ADC acquisition chip U6 and is grounded through non-polar capacitor C4. The output terminal of ADC acquisition chip U6 is connected to the SPI terminal of the controller.
[0010] This invention also discloses a portable 4-20mA calibration method using the aforementioned calibration device. The method includes the following steps: Step 1: Connect the calibration device to the RS485 interface of the device, and connect the calibration device's 4-20mA measurement cable to the device's 4-20mA output port. Step 2: After connecting, click "Start" on the main control screen. The control light will turn yellow. The main control screen will write 2019 and 2006 to registers 33 and 34 of the device in sequence. After receiving the data, the device will enter the 4-20mA production calibration mode and write 1 to both registers 33 and 34. Check registers 33 and 34 on the main control screen. If they do not become 1 after 30 seconds, the main control screen will display "Failed to enter production mode" and the control light will turn red. Step 3: After registers 33 and 34 return 1, the main control screen sends instruction 61 to register 35 of the device. After receiving it, the device outputs 4mA. The main control screen waits for 10 seconds to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the main control screen. The main control screen judges the range of the measured value. If the range is not within 2-6mA, the main control screen prompts a 4-20mA fault and lights up a red light. If it is within the 2-6mA range, the measured value is sent to registers 36 and 37 of the device. Step 4: After sending, the main control screen sends instruction 62 to register 35 of the device. After receiving it, the device outputs 10mA. The main control screen waits for 10 seconds to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the main control screen. The main control screen judges the range of the measured value. If the range is not 8-12mA, the main control screen prompts a 4-20mA fault and lights up a red light. If it is within the 8-12mA range, the measured value is sent to registers 36 and 37 of the device. Step 5: After sending, the main control screen sends instruction 63 to register 35 of the device. After receiving it, the device outputs 20mA. The main control screen waits for 10 seconds to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the main control screen. The main control screen judges the range of the measured value. If the range is not 18-22mA, the main control screen prompts a 4-20mA fault and lights up a red light. If it is in the 8-12mA range, the measured value is sent to registers 38 and 37 of the device. Step 6: After completion, the main control screen sends the 66 command to register 35 of the device. After receiving the 66 command, the device saves the calibration parameters and writes 88 into register 38 to indicate success.
[0011] The aforementioned portable 4-20mA calibration method also includes retesting: Step 7: After the main control screen reads 88 from register 38, it begins the retest. The main control screen writes 81 to register 35. After receiving the instruction, the device outputs 6mA. The main control screen waits 10 seconds for it to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the retest value on the main control screen. The main control screen judges the range of the measured value. If the absolute value is greater than 0.02mA, the main control screen prompts that the 4-20mA retest is out of tolerance and lights up a red light. If the absolute value is less than 0.02mA, it continues to retest the next value. Write instruction 82 to retest 8mA; Write instruction 83 to retest 14mA; Write instruction 84 to retest 18mA; The retest ends after the last value is retested. The absolute value of the difference between all measured values and the calibration point must be less than 0.02mA to indicate successful calibration. At the same time, a green light will illuminate, and 2099 and 2006 will be written to registers 33 and 34 respectively. The equipment will then exit production calibration. If the retest exceeds 0.02mA, the calibration will terminate, indicating that the 4-20mA retest is out of tolerance, and a red light will illuminate.
[0012] Compared with the prior art, the present invention has the following advantages: the device of the present invention is easy to operate, improves efficiency, reduces labor costs and labor time, is easy to carry, and can detect and troubleshoot instruments or electrodes with inaccurate 4-20mA outputs in real time for inventory tables or electrodes that have been stored for too long. At the same time, it can also calibrate in real time for instruments at the customer's site. The calibration device can meet relatively harsh environments, has good performance, and is easy to promote and use.
[0013] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0014] Figure 1 This is a schematic diagram of the overall structure of the device of the present invention.
[0015] Figure 2 This is a schematic diagram of the internal components of the device of the present invention.
[0016] Figure 3 This is a schematic diagram of the human-computer interaction interface of the present invention.
[0017] Figure 4 This is a schematic diagram of the power supply circuit module of the present invention.
[0018] Figure 5 This is a schematic diagram of the signal acquisition circuit module of the present invention.
[0019] Explanation of reference numerals in the attached figures: 1—Housing; 2—Touchscreen; 3—Controller; 4—Power supply circuit module; 5—Signal acquisition circuit module. Detailed Implementation
[0020] like Figure 1 and Figure 2 As shown, the portable 4-20mA calibration device of the present invention includes a device body and a control system. The device body includes a housing 1, and the control system is installed inside the housing 1. A touch screen 2 is provided on the top of the housing 1, and multiple connecting wires are provided on the side of the housing 1. The control system includes a controller 3 and a power supply circuit module 4 for supplying power to the control system. The input terminal of the controller 3 is connected to a signal acquisition circuit module 5, and the touch screen 2 is connected to the controller 3.
[0021] In this embodiment, the multiple connecting lines include two signal lines, two data lines, and one power line.
[0022] In this embodiment, the two signal lines are RS485-1 and RS485-2. RS485-1 is used to communicate with the instrument under test or the electrode; RS485-2 is used to communicate between the touch screen 2 and the current measuring device.
[0023] In this embodiment, as Figure 3 As shown, the touch screen 2 is equipped with a human-machine interface, which includes a parameter setting module, a button module, an indicator light module, a parameter display module, and an information prompt module. The parameter setting module and the button module send control commands to the controller 3, and the indicator light module, the parameter display module, and the information prompt module display the device status returned by the controller 3.
[0024] In practical implementation, the device connects the instrument and electrode. The calibration device clicks "Start," controlling the instrument or electrode to enter calibration mode. The calibration device then controls the instrument or electrode to output 4mA, 10mA, and 20mA respectively. The current measuring device collects the signals, converts them, and sends them to the main control screen via RS485. The values are displayed on the main control screen, which then sends the values back to the instrument or electrode via RS485. Through three-point calibration (calibration points are 4mA, 10mA, and 20mA), the values of a and b are calculated using the linear equation y=ax+b. The instrument or electrode then saves these values. When the instrument or electrode outputs 4-20mA, output correction is performed using slope and offset. This calibration device is applicable to all instruments and electrodes developed by this company.
[0025] In this embodiment, as Figure 4As shown, the power supply circuit module 4 includes a power interface J1, a DC-DC power chip U1, a DC-DC boost chip U3, an LDO buck chip U4, a lithium battery BT1, non-polar capacitors C1, C2, and C3, and a button K1. The input terminal of the DC-DC power chip U1 is connected to pin 1 of the power interface J1 and grounded through non-polar capacitor C1. Pins 2 and 3 of the power interface J1 are both grounded. The positive terminal of the lithium battery BT1, one end of the non-polar capacitor C2, and one end of the button K1 are all connected to the output terminal of the DC-DC power chip U1. The negative terminal of the lithium battery BT1 and the other end of the non-polar capacitor C2 are both grounded. The other end of the button K1 is connected to the input terminals of both the DC-DC boost chip U3 and the LDO buck chip U4 and grounded through non-polar capacitor C3. The output terminal of the DC-DC boost chip U3 powers the touch screen 2, and the output terminal of the LDO buck chip U4 powers the acquisition circuit module 5.
[0026] In practical implementation, the power supply is DC 24V. After being connected to the device through power interface J1, the voltage is regulated and filtered by non-polar capacitor C1, then stepped down to 5V by DC-DC power chip U1 to charge lithium battery BT1. The lithium battery is connected to non-polar capacitor C2 for voltage regulation, and then connected to button K1. K1 is then connected to non-polar capacitor C3 for voltage regulation and filtering. The voltage is then boosted and bucked through two branches. Branch 1 connects to DC-DC boost chip U3 to boost the voltage to 24V to power the screen display, and branch 2 connects to LDO buck chip U4 to step down the voltage to 3.3V to power the analog acquisition section. Before use, this device only needs to ensure that the lithium battery has a certain amount of charge to be portable to many locations to complete 4-20mA production calibration work, making it highly portable. A second advantage is that using an independent lithium battery power supply avoids interference from the 220V mains power grid, providing strong anti-interference capabilities.
[0027] In this embodiment, as Figure 5As shown, the signal acquisition circuit module 5 includes an operational amplifier U5, an ADC acquisition chip U6, resistors R1, R2, R3, R4, R5, R6, and a non-polarized capacitor C4. The fourth pin of the operational amplifier U5 is connected to the negative terminal of the 4-20mA output of the instrument under test or electrode via resistor R2, and is also connected to one end of resistor R1. The third pin of the operational amplifier U5 is connected to the positive terminal of the 4-20mA output of the instrument under test or electrode via resistor R4, and is also connected to the other end of resistor R1. One end of resistor R5 is connected to the 5th pin of operational amplifier U5 and the other end of resistor R5. The 2nd pin of operational amplifier U5 is connected to VCC_3.3V voltage. The 1st pin of operational amplifier U5 is connected to one end of resistor R6 and is connected to the 4th pin of operational amplifier U5 through resistor R3. The other end of resistor R6 is connected to the input terminal of ADC acquisition chip U6 and is grounded through non-polar capacitor C4. The output terminal of ADC acquisition chip U6 is connected to the SPI terminal of controller 3.
[0028] In practice, the 4-20mA output terminal of the instrument or electrode is connected to the positive and negative terminals shown on the port. The current output signal is connected to a sampling resistor R1 with a resistance of 100Ω. When current flows through resistor R1, a voltage drop U will be generated across the resistor. The voltage signal generated by the 4-20mA amplifier is between 0.4V and 2V. By acquiring the magnitude of the voltage signal, the actual value of the current signal can be calculated. The upper end of resistor R1 is connected to resistor R2, which is then connected to pin 4 of the negative input of operational amplifier U5. The negative input of operational amplifier U5 is connected to pin 1 of the output. The lower end of resistor R1 is connected to resistor R4, which is then connected to pin 3 of the positive input of U5. Finally, the positive input is connected to resistor R5 and then to ground. This circuit is a differential amplifier circuit. The resistance values of resistors R2, R3, R4, and R5 are equal. The gain of the differential amplifier is 1, therefore the acquired signal value is the voltage difference across resistor R1. Pin 1 of the output terminal of U5 is connected to R6 and non-polar capacitor C4 to complete signal filtering. It is then connected to the high-precision ADC acquisition chip U6 to convert the voltage signal into a digital signal. U6 communicates with controller 3 (U7) via SPI. Then, controller 3 connects to MAX485 chip U8 to transmit the data to the display screen via RS485. Finally, the display screen transmits the data to the instrument or electrode and displays it.
[0029] The high-resolution ADC acquisition chip ensures the accuracy of the current signal. For signal calibration, there are three default calibration points: 4mA, 10mA, and 20mA. The ADC value of the acquired signal satisfies a linear relationship with the default output value of the instrument or electrode: y=kx+b (Note: The default value is the theoretical output signal of the internal controller of the instrument or electrode, without considering deviations within the circuit and chip, therefore calibration is required). The software design employs segmented calibration, with one calibration line from 4mA to 10mA and another from 10mA to 20mA, thus ensuring the accuracy of the current calibration.
[0030] After the instrument or electrode is connected to the calibration device, press the K1 button to complete the communication. The device will then output 4mA, 10mA, and 20mA signals on the screen. The instrument or electrode will receive the instruction of the default output value and then complete the output. The output of each default value satisfies the following block diagram. After the ADC signals of the three default values are acquired, they will be transmitted to the electrode or instrument through the screen. The instrument or electrode will perform internal calculations using the ADC value to perform calibration. After calibration, the accuracy of the output retest point will be used to verify whether the calibration was successful.
[0031] A portable 4-20mA calibration method of the present invention includes the following steps: Step 1: Connect the calibration device to the RS485 interface of the device, and connect the calibration device's 4-20mA measurement cable to the device's 4-20mA output port. Step 2: After connecting, click "Start" on the main control screen. The control light will turn yellow. The main control screen will write 2019 and 2006 to registers 33 and 34 of the device in sequence. After receiving the data, the device will enter the 4-20mA production calibration mode and write 1 to both registers 33 and 34. Check registers 33 and 34 on the main control screen. If they do not become 1 after 30 seconds, the main control screen will display "Failed to enter production mode" and the control light will turn red. Step 3: After registers 33 and 34 return 1, the main control screen sends instruction 61 to register 35 of the device. After receiving it, the device outputs 4mA. The main control screen waits for 10 seconds to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the main control screen. The main control screen judges the range of the measured value. If the range is not within 2-6mA, the main control screen prompts a 4-20mA fault and lights up a red light. If it is within the 2-6mA range, the measured value is sent to registers 36 and 37 of the device. Step 4: After sending, the main control screen sends instruction 62 to register 35 of the device. After receiving it, the device outputs 10mA. The main control screen waits for 10 seconds to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the main control screen. The main control screen judges the range of the measured value. If the range is not 8-12mA, the main control screen prompts a 4-20mA fault and lights up a red light. If it is within the 8-12mA range, the measured value is sent to registers 36 and 37 of the device. Step 5: After sending, the main control screen sends instruction 63 to register 35 of the device. After receiving it, the device outputs 20mA. The main control screen waits for 10 seconds to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the main control screen. The main control screen judges the range of the measured value. If the range is not 18-22mA, the main control screen prompts a 4-20mA fault and lights up a red light. If it is in the 8-12mA range, the measured value is sent to registers 38 and 37 of the device. Step 6: After completion, the main control screen sends the 66 command to register 35 of the device. After receiving the 66 command, the device saves the calibration parameters and writes 88 into register 38 to indicate success.
[0032] Step 7: After the main control screen reads 88 from register 38, it begins the retest. The main control screen writes 81 to register 35. After receiving the instruction, the device outputs 6mA. The main control screen waits 10 seconds for it to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the retest value on the main control screen. The main control screen judges the range of the measured value. If the absolute value is greater than 0.02mA, the main control screen prompts that the 4-20mA retest is out of tolerance and lights up a red light. If the absolute value is less than 0.02mA, it continues to retest the next value. Write instruction 82 to retest 8mA; Write instruction 83 to retest 14mA; Write instruction 84 to retest 18mA; The retest ends after the last value is retested. The absolute value of the difference between all measured values and the calibration point must be less than 0.02mA to indicate successful calibration. At the same time, a green light will illuminate, and 2099 and 2006 will be written to registers 33 and 34 respectively. The equipment will then exit production calibration. If the retest exceeds 0.02mA, the calibration will terminate, indicating that the 4-20mA retest is out of tolerance, and a red light will illuminate.
[0033] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.
Claims
1. A portable 4-20mA calibration device, characterized in that: The device includes a main body and a control system. The main body includes a housing (1), the control system is installed inside the housing (1), a touch screen (2) is provided on the top of the housing (1), and multiple connecting wires are provided on the side of the housing (1). The control system includes a controller (3) and a power supply circuit module (4) for supplying power to the control system. The input terminal of the controller (3) is connected to a signal acquisition circuit module (5), and the touch screen (2) is connected to the controller (3).
2. The portable 4-20mA calibration device according to claim 1, characterized in that: The multiple connecting lines include two signal lines, two data lines, and one power line.
3. The portable 4-20mA calibration device according to claim 2, characterized in that: The two signal lines are RS485-1 and RS485-2. RS485-1 is used to communicate with the instrument under test or the electrode; RS485-2 is used to communicate between the touch screen (2) and the current measuring device.
4. The portable 4-20mA calibration device according to claim 1, characterized in that: The touch screen (2) is equipped with a human-machine interface, which includes a parameter setting module and a button module, as well as an indicator light module, a parameter display module and an information prompt module. The parameter setting module and the button module send control commands to the controller (3), and the indicator light module, the parameter display module and the information prompt module display the device status returned by the controller (3).
5. The portable 4-20mA calibration device according to claim 1, characterized in that: The power supply circuit module (4) includes a power interface J1, a DC-DC power chip U1, a DC-DC boost chip U3, an LDO buck chip U4, a lithium battery BT1, a non-polar capacitor C1, a non-polar capacitor C2, a non-polar capacitor C3, and a button K1. The input terminal of the DC-DC power chip U1 is connected to the first pin of the power interface J1 and is grounded through the non-polar capacitor C1. The second and third pins of the power interface J1 are both grounded. The positive terminal of the lithium battery BT1, one end of the non-polar capacitor C2, and one end of the button K1 are all connected to the output terminal of the DC-DC power chip U1. The negative terminal of the lithium battery BT1 and the other end of the non-polar capacitor C2 are both grounded. The other end of the button K1 is connected to the input terminal of the DC-DC boost chip U3 and the input terminal of the LDO buck chip U4 and is grounded through the non-polar capacitor C3. The output terminal of the DC-DC boost chip U3 powers the touch screen (2), and the output terminal of the LDO buck chip U4 powers the acquisition circuit module (5).
6. The portable 4-20mA calibration device according to claim 1, characterized in that: The signal acquisition circuit module (5) includes an operational amplifier U5, an ADC acquisition chip U6, resistors R1, R2, R3, R4, R5, R6, and a non-polarized capacitor C4. The fourth pin of the operational amplifier U5 is connected to the negative terminal of the 4-20mA output of the instrument under test or electrode via resistor R2, and is also connected to one end of resistor R1. The third pin of the operational amplifier U5 is connected to the positive terminal of the 4-20mA output of the instrument under test or electrode via resistor R4, and is also connected to the other end of resistor R1 and resistor C4. One end of R5 is connected to the other end of the operational amplifier U5. The 5th pin of the operational amplifier U5 and the other end of the resistor R5 are connected to the other end of the operational amplifier U5. The 2nd pin of the operational amplifier U5 is connected to the VCC_3.3V voltage. The 1st pin of the operational amplifier U5 is connected to one end of the resistor R6 and is connected to the 4th pin of the operational amplifier U5 through the resistor R3. The other end of the resistor R6 is connected to the input terminal of the ADC acquisition chip U6 and is grounded through the non-polar capacitor C4. The output terminal of the ADC acquisition chip U6 is connected to the SPI terminal of the controller (3).
7. A portable 4-20mA calibration method, characterized in that, Using the calibration apparatus as described in any one of claims 1-6, the method comprises the following steps: Step 1: Connect the calibration device's RS485 interface to the device's RS485 interface, and connect the calibration device's 4-20mA measurement cable to the device's 4-20mA output port. Step 2: After connecting, click "Start" on the main control screen. The control light will turn yellow. The main control screen will write 2019 and 2006 to registers 33 and 34 of the device in sequence. After receiving the data, the device will enter the 4-20mA production calibration mode and write 1 to both registers 33 and 34. Check registers 33 and 34 on the main control screen. If they do not become 1 after 30 seconds, the main control screen will display "Failed to enter production mode" and the control light will turn red. Step 3: After registers 33 and 34 return 1, the main control screen sends instruction 61 to register 35 of the device. After receiving it, the device outputs 4mA. The main control screen waits for 10 seconds to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the main control screen. The main control screen judges the range of the measured value. If the range is not within 2-6mA, the main control screen prompts a 4-20mA fault and lights up a red light. If it is within the 2-6mA range, the measured value is sent to registers 36 and 37 of the device. Step 4: After sending, the main control screen sends instruction 62 to register 35 of the device. After receiving it, the device outputs 10mA. The main control screen waits for 10 seconds to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the main control screen. The main control screen judges the range of the measured value. If the range is not 8-12mA, the main control screen prompts a 4-20mA fault and lights up a red light. If it is within the 8-12mA range, the measured value is sent to registers 36 and 37 of the device. Step 5: After sending, the main control screen sends instruction 63 to register 35 of the device. After receiving it, the device outputs 20mA. The main control screen waits for 10 seconds to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the main control screen. The main control screen judges the range of the measured value. If the range is not 18-22mA, the main control screen prompts a 4-20mA fault and lights up a red light. If it is in the 8-12mA range, the measured value is sent to registers 38 and 37 of the device. Step 6: After completion, the main control screen sends the 66 command to register 35 of the device. After receiving the 66 command, the device saves the calibration parameters and writes 88 into register 38 to indicate success.
8. The portable 4-20mA calibration method according to claim 7, characterized in that, This also includes retesting: Step 7: After the main control screen reads 88 from register 38, it begins the retest. The main control screen writes 81 to register 35. After receiving the instruction, the device outputs 6mA. The main control screen waits 10 seconds for it to stabilize. After 10 seconds, the main control screen reads the 4-20mA output value and displays the measured value on the retest value on the main control screen. The main control screen judges the range of the measured value. If the absolute value is greater than 0.02mA, the main control screen prompts that the 4-20mA retest is out of tolerance and lights up a red light. If the absolute value is less than 0.02mA, it continues to retest the next value. Write instruction 82 to retest 8mA; Write instruction 83 to retest 14mA; Write instruction 84 to retest 18mA; The retest ends after the last value is retested. The absolute value of the difference between all measured values and the calibration point must be less than 0.02mA to indicate successful calibration. At the same time, a green light will illuminate, and 2099 and 2006 will be written to registers 33 and 34 respectively. The equipment will then exit production calibration. If the retest exceeds 0.02mA, the calibration will terminate, indicating that the 4-20mA retest is out of tolerance, and a red light will illuminate.