Pressure transmitter calibration process, verification items, and technical specifications

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This post shares the calibration procedure for pressure transmitters in use. Each step of this calibration process involves different calibration tasks and technical standards, which must be strictly followed by those responsible for calibrating the transmitters. Pressure transmitter yunrun.com.cn/product/list_84.html I. Preparations before calibrating the transmitter When calibrating a pressure transmitter with a low range, it is important to eliminate the influence of fluid column differences ； If there is a water column correction, the value of this correction should be added during calibration ； When the pressure-transmitting medium is a liquid, the geometric center of the pressure tap on the pressure transmitter must be at the same horizontal level as the lower surface of the piston in the piston-type pressure gauge (or the geometric center of the pressure tap on the standard device). 1. Verification before calibrating the pressure transmitter: ① Preheat it according to the time specified by the manufacturer of the pressure transmitter ； If not specified by the manufacturer, it is possible to preheat for 15 minutes (30 minutes for instruments with automatic reference temperature compensation) before performing the preliminary verification of the pressure transmitter. ②Verification is carried out on the main scale lines or at integer points ； Unless otherwise specified, the number of check points shall include at least 5 points, namely the lower limit, upper limit, and common points. ③The verification starts from the lower limit value; the input signal is gradually increased so that the pointer or displayed digits come to rest slowly at each main scale value of the instrument under test (to avoid any overshoot or rebound), up to the upper limit of the range. After that, the input signal is gradually decreased to carry out the verification in the downward direction, until the lower limit of the range is reached. During the process, the readings of the standard instruments are read and recorded separately (except for pressure gauge calibration). Among them, the upper limit value is only used to check the upward stroke, while the lower limit value is only used to check the downward stroke ； And keep a record of it. ④For instruments that are not faulty, no adjustments of any kind shall be made before verification is completed prior to calibration. ⑤For pressure transmitters whose verification results before calibration show that the basic error of the indicated value is less than or equal to the allowable error for that indicated value, it is not necessary to perform zero and full-scale adjustments. 2. Inspection of the pressure transmitter’s sealing performance: ① After the pressure transmitter is tightly connected to the pressure calibrator, increase the pressure (or reduce it) gradually until the pressure in the transmitter’s measurement chamber reaches the upper limit of measurement (or 90% of the local atmospheric pressure in the case of reduced pressure). Then close the isolation valve and keep the system sealed for 15 minutes. During the last 5 minutes, the pressure value must not decrease (or increase) by more than 2% of the upper measurement limit. ②During the sealing test of a differential pressure transmitter, the high and low pressure chambers are connected, and the rated operating pressure is applied to observe the result. 3. Static pressure error test for differential pressure transmitters (whether this test is conducted depends on the transmitter). ① A static pressure error test should be carried out on differential pressure transmitters after replacing the elastic elements, reassembling the mechanical parts, or changing the measurement range. ②When using a piston pressure gauge as the pressure source, an oil-water separator should be installed before connecting the transmitter. ③Connect the high and low pressure chambers of the differential pressure transmitter and expose them to atmospheric pressure, then measure the lower limit value of the output. By introducing static pressure and gradually changing it from atmospheric pressure to the rated operating pressure, after stabilizing for 3 minutes, the lower limit of the output is measured. The difference between this value and the lower limit of the output at atmospheric pressure represents the effect of static pressure; this value should not exceed the limits specified by the manufacturer. ④If the actual operating static pressure of the transmitter is lower than its rated static pressure, the static pressure error can be determined by testing with the actual operating static pressure. ⑤If the static pressure error exceeds the specified value, the zero point should be adjusted after depressurization to re-perform the static pressure error adjustment. http://yunrun.com.cn/upload/201703/19/201703191754011618.jpg Monocrystalline silicon transmitters, YR-ER100 series. II. Transmitter calibration items and technical standards 1. Zero and full-scale calibration ① When a pressure signal at the lower limit is input, adjust the transmitter’s output current to the physical zero point ； When the pressure is increased to the upper limit pressure signal value, adjust the output current to full scale, and repeat the adjustment until both meet the requirements. ②Adjust the zero point positively or negatively according to the operating requirements. ③During the initial calibration of an intelligent pressure transmitter, the physical quantity to be measured should be applied for calibration; subsequent calibrations can be carried out using a handheld operator. During arbitration calibration, pressure calibration is required in principle. ④Adjust the zero point and full scale repeatedly until the accuracy requirements are met; the basic error value, return error value of the transmitter, as well as the changes in the open-circuit output range shall meet the requirements specified in Table 1. Table 1: Table of allowable error values for transmitters. Accuracy classes: 0.25, 0.5, 1.0, 1.5, 2.5. Basic error (%): ±0.25, ±0.5, ±1.0, ±1.5, ±2.5. Hysteresis error (%): 0.2, 0.4, 0.8, 1.2, 2.0. Output open-circuit range variation (%): 0.1, 0.25, 0.4, 0.6, 1.0. ⑤ For flow transmitters, when the differential pressure signal is below 9%, the basic error and hysteresis error values are not applicable. 2. Inspection after transmitter calibration: The steps for inspection after calibration are the same as steps ① to ③ of the verification before calibration. 3. Issue a pressure transmitter calibration report: A formal calibration report is issued based on the laboratory’s calibration results, and this report must be signed in person by the calibrator. III. Operation after transmitter calibration 1. Turn off the power to the pressure transmitter being calibrated and to the calibration equipment (this step is not required for instruments that do not require power). 2. For instruments installed on-site, the exposed adjustment mechanisms for zero point, range, and alarm values should be sealed with paint, and valid metrological labels should be attached to them. 3. Organization of verification records before calibration and calibration records after calibration for pressure transmitters. 4. Install the pressure transmitter back in place and restore the wiring. Changhui Instruments yunrun.com.cn