Calibration methods for intelligent pressure transmitters including range reset, sensor calibration, and fine tuning of the analog output

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Calibrating an intelligent pressure transmitter essentially involves resetting the range, calibrating the sensor, and fine-tuning the analog output. This post provides a detailed explanation of the methods and steps for resetting the range, calibrating the sensor, and fine-tuning the analog output of intelligent pressure transmitters, for everyone’s reference. 1. Wiring for calibrating smart pressure transmitters: The wiring for calibrating smart pressure transmitters is shown in the figure below. When a piston-type pressure gauge is used as the standard instrument, it serves both as the pressure source and as the standard instrument, so there is no need for the standard pressure gauge shown in the diagram. http://yunrun.com.cn/upload/201906/15/201906150203320406.png Pressure transmitters: yunrun.com.cn/product/list_84.html 2. Calibration methods for intelligent pressure transmitters: This article uses the 3051 transmitter as an example to explain the calibration methods. Calibrating an analog transmitter can be completed in one step, while calibrating an intelligent pressure transmitter requires three steps: ◆ Reset the range by setting the 4mA and 20mA points at the desired pressures. ◆Sensor calibration, also known as sensor fine-tuning, aims to adjust the factory-characterized curve so that the transmitter achieves optimal performance within a specific pressure range. ◆Analog output tuning refers to adjusting the analog output so that it matches the control loop. ①The intelligent pressure transmitter allows for the reset of the range; the range values can be set at the 4mA and 20mA points, which correspond to the lower and upper limits of the range. Regardless of the set range, the sensor inside the smart pressure transmitter will measure and record the actual value of the input parameter. Assume that 4mA and 20mA correspond to 0 and 10kPa, but when the smart pressure transmitter detects an input pressure of 25kPa, it will digitally output a reading of 25kPa along with a percentage of the range of 250%. There are three ways to reset the range: A. Set the range using only the handheld controller. Using only the hand controller to set the range is the simplest method. This operation does not require any pressure input; simply using shortcut keys 4 or 5 on the HART handheld device is sufficient to change the 4mA and 20mA values of the intelligent pressure transmitter. B. Set the range using a pressure source and a hand controller. Use the HART handheld controller shortcut key sequence 1, 2, 3, 1, 2. If the specific values for the 4mA and 20mA points are unknown, the range can be set using the handheld controller and the pressure source; by entering the aforementioned sequence of shortcut commands and following the instructions in the HART handheld controller’s online menu, the values for 4mA and 20mA can be modified. C. Set the range using the “zero” and “range” buttons of the pressure source and transmitter. This method is commonly used when the exact values of the 4mA and 20mA points are unknown, and there is no handheld controller available. Follow these steps: a. Loosen the screws holding the label on top of the cover of the intelligent pressure transmitter, remove the label, and the zero and range buttons will become visible ； b. Allow the high-pressure chamber of the intelligent pressure transmitter to be exposed to atmospheric pressure (i.e., set the input pressure at the lower range limit to 0), then press the “Zero” button for 2 seconds and check whether the output is 4mA. If there is a header, the header will show that zero has been passed ； c. Use a pressure source with sufficient accuracy to apply a pressure value corresponding to the upper range limit to the high-pressure chamber of the intelligent pressure transmitter. Press the “Range” button for 2 seconds and check whether the output is 0mA. If there is a header, the header will indicate that the range has been passed. Reasons why it is not possible to adjust the zero point and range: The zero point and range cannot be adjusted when the protection jumper switch of the smart pressure transmitter is in the “ON” position. If the software is set to prevent local zero and range adjustments, then the local zero and range buttons cannot be used for such adjustments either. By using the command sequence 1, 4, 4, 1, 7 on the HART handheld communicator, it is possible to activate or deactivate the zero and range buttons on the intelligent pressure transmitter. But at this time, the HART communicator can still be used to change the transmitter’s configuration. ②Calibration of intelligent pressure transmitter sensors: Sensor calibration refers to the fine-tuning of sensors using full-scale adjustment or zero-point adjustment functions. The use of these two functions depends on the application, and both can alter the response of the smart transmitter to input signals. A. Fine adjustment of the zero point of intelligent pressure transmitters: This type of adjustment is a single-point adjustment that helps to compensate for the effects of the installation location; it allows for fine tuning of intelligent pressure transmitters installed on-site. This correction can maintain the slope of the characteristic curve; therefore, it should not be used to replace full-scale trimming across the entire range of the sensor. When performing zero-point fine tuning, ensure that the balance valve is in the open position and that the pressures on the high and low sides of the transmitter are equal. Fine-tuning of the sensor zero point can be performed using the command sequence 1, 2, 3, 3, 1 via the HART handheld device’s shortcut keys. The operation steps are as follows: a. Breathe air into the transmitter and connect the handheld controller to the measurement circuit. From the main menu of the handheld controller, select 1. Device Setup, 2. Diagnostics and Service, 3. Calibration, 3. Sensor Trim, and 1. Zero Trim to prepare for zero trimming. c. Perform the zero-point fine-tuning adjustment according to the instructions displayed on the operator panel. B. Fine tuning of the intelligent pressure transmitter over the entire range: Fine tuning over the entire range (also known as full-scale tuning) is a type of calibration for two-point sensors, involving the application of pressure at both the start and end points of the range, with all outputs between them being linearized. First, adjust the low fine-tuning value to establish the correct offset. The adjustment for high fine-tuning values provides a slope correction based on the characteristic curve of low fine-tuning values. The characterization curves established at the time of manufacturing will not be altered by this program. Fine-tuning the sensor over its full range is carried out by using the command sequences 1, 2, 3, 3 via the HART handheld device’s shortcut keys. The operation steps are as follows: a. On the main menu of the controller, enter the shortcut key sequence below Full Trim: 1. Device Setup, 2. Diagnostics and Service, 3. Calibration, 4. Sensor Trim. b. Select 2. Lower sensor Trim to adjust the lower limit trim point. c. Select the pressure input value such that the lower limit is equal to or less than 4 mA, and adjust the lower limit according to the instructions displayed on the handheld controller. d. Repeat the above steps to adjust the upper limit value, using 3. Upper Sensor Trim in place of 2. Lower Sensor Trim from step b. e. Select the pressure input value so that the upper limit is equal to or greater than 20mA, and adjust the upper limit according to the instructions displayed on the handheld controller. ③Fine tuning of the analog output of intelligent pressure transmitters: Analog output fine tuning refers to the calibration of the 4-20mA analog output. It involves using the “Analog Output Trim” command to adjust the 4-20mA current output of the transmitter so that it meets the factory standards. This instruction can adjust the number/modulus signal conversion. The following describes the steps for digital/analog fine-tuning. A. From the HOME main screen, select 1. Device Setup, 2. Diagnostics and Service, 3. Calibration, 2. Trim Analog Output, 1. Digital-Analog. After setting the control loop to manual mode, select “OK”. B. When the CONNECT REFERENCE METER prompt appears, connect a standard ammeter to the smart pressure transmitter; connect the positive lead of the ammeter to the positive terminal of the transmitter, and the negative lead to the negative terminal of the smart pressure transmitter. C. After connecting the reference table, select “OK”. D. Under the prompt \"SETTING FLD DEV OUTPUT TO 4MA\" (set the output of the field device to 4mA), click \"OK\" to confirm, and the smart pressure transmitter will output 4.00mA. E. Record the actual value from the standard table, and enter that value when the ENTER METER VALUE prompt appears. The handheld controller will prompt: Verify whether the output value is equal to the value in the reference table. F. If the value on the standard table is equal to the transmitter’s output value, select Yes; otherwise, select No. If Yes is selected, you can proceed to the next step. If No is selected, repeat Step E. G. Under the prompt \"SETTING FLD DEV OUTPUT TO 20MA\" (set the output of the field device to 20mA), click OK, and repeat steps E and F until the value in the reference table is equal to the output value of the intelligent pressure transmitter. H. After returning the control loop to automatic control mode, click OK to confirm. ④For fine-tuning digital-to-analog conversion using different scales, use the HART handheld device’s shortcut keys 1, 2, 3, 2, 2; this sequence allows for digital-to-analog fine-tuning with alternative scales. The Scaled D/A Trim command is used to align the 4 and 20mA points with a reference scale selected by the user, rather than with 4 and 20mA directly; when measured through a 250Ω load resistor, this results in a voltage range of 1-5V ； Or, when measured via DCS, it is 0-100%. When performing digital/analog fine-tuning based on the scale, a standard ammeter should be connected to the transmitter, and the output signal should be fine-tuned to the desired scale according to the instructions in the \"Analog Output Fine-Tuning\" step. ⑤Select sensor trimming or analog output trimming. When carrying out the trimming process, it is necessary to first determine whether it is the analog-to-digital conversion section of the intelligent pressure transmitter’s circuit board that needs to be calibrated, or the digital-to-analog conversion section. The following steps can be followed: A. Connect the pressure source, HART communicator, and digital reading device to the transmitter ； And establish communication between the intelligent pressure transmitter and the handheld operator. B. Enter the pressure corresponding to the upper range limit of the intelligent pressure transmitter. C. Compare the applied pressure with the process variable (PV) displayed on the operator panel’s menu; if the PV value on the operator panel does not match the applied pressure, then sensor fine-tuning can be performed. D. Compare the analog output AO on the operator’s online menu with the reading on the digital gauge. If the AO reading on the hand controller does not match the reading on the digital gauge, output fine-tuning can be performed. E. Before performing the fine-tuning operations in steps C and D, it is necessary to verify the accuracy of the testing instruments being used, such as pressure readings and digital gauge readings; otherwise, incorrect adjustments will occur.