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I. Preparation Work: We know that pressure transmitters are connected to pressure conduits in practical applications. The usual approach is to disconnect the connection between the pressure conduit and the pressure transmitter, and then connect it to a pressure source for calibration. This is very troublesome, and the workload and effort required are high. The biggest concern is that the pressure guide tube might break or leaks could occur during the installation and removal of the connectors. We know that for pressure transmitters of any model, both the positive and negative pressure chambers are equipped with exhaust and drain valves or plugs ； This facilitates on-site calibration of the pressure transmitter, meaning that it can be calibrated without having to remove the pressure guide tube. When calibrating the pressure transmitter, first close the positive and negative valves of the three-valve assembly, open the balance valve, then loosen the exhaust and drain valves or cocks to release pressure, and use a custom-made connector to replace the exhaust and drain valves or cocks in the positive pressure chamber ； The negative pressure chamber, on the other hand, remains loose to allow it to be in contact with the atmosphere. The pressure source is connected to the custom-made connector through a rubber hose; the balance valve is closed, and the airtightness of the gas circuit is checked. Then, an ammeter (voltage meter) and a HART handheld controller produced by Mingyu Automatic Control are connected to the transmitter’s output circuit. After powering on and warming up the system, calibration begins. II. Calibration of conventional pressure transmitters: First, set the damping to zero; adjust the zero point first, and then apply the full-scale pressure to set the range so that the output is 20mA. On-site calibration is meant to be carried out quickly, and here a fast method for adjusting the zero point and the range is described. Zero adjustment has almost no effect on full scale, but adjusting the full scale does affect the zero point. In the absence of drift, this effect is approximately 1/5 of the range adjustment amount; that is, if the range is increased by 1 mA, the zero point will shift upward by about 0.2 mA, and vice versa. For example: if the full-scale pressure is 100 KPa and the corresponding reading is 19.900 mA, adjust the range potentiometer so that the output becomes 19.900 mA; then (20.000 – 19.900) * 1.25 = 20.025 mA. An increase of 0.125 mA in the range results in an increase of 1/5 * 0.125 = 0.025 in the zero point. Adjust the zero-point potentiometer to make the output 20.000 mA. Once the zero point and full scale have been properly adjusted, check the intermediate scales to see if they are within the specified range Make fine adjustments if necessary. Then, adjustments for migration, linearity, and damping are carried out. III. Calibration of intelligent pressure transmitters: It is not possible to calibrate intelligent transmitters using the conventional methods mentioned above, as this is determined by the structural principles of the HART communicator. Because in an intelligent transmitter, between the input pressure source and the generated 4-20mA current signal, in addition to mechanical and electrical components, there is also a microprocessor chip that performs calculations on the input data. Therefore, the tuning differs from conventional methods. In fact, manufacturers also provide instructions for calibrating smart transmitters; for example, ABB’s transmitters offer options such as “setting the range,” “resetting the range,” and “fine tuning.” The “set range” operation is primarily carried out by setting the values for LRV and URV to complete the configuration, whereas the “reset range” operation requires connecting the transmitter to a standard pressure source; through a series of instructions, the transmitter directly senses the actual pressure and sets the corresponding value. The initial and final settings of the range depend directly on the actual pressure input value. However, it should be noted that although the analog output of the transmitter corresponds correctly to the input value used, the digital reading of the process value will show a slight difference, which can be calibrated using the fine-tuning option. Since each component needs to be tuned individually as well as in combination with the others. Therefore, the actual calibration can be carried out following these steps: 1. First, perform a 4-20mA fine-tuning to calibrate the D/A converter inside the transmitter; since this process does not involve any sensing components, no external pressure signal source is required. 2. Perform another full-scale fine adjustment to ensure that the 4-20mA signal and the digital readings correspond to the actual pressure signal applied; therefore, a pressure signal source is required. 3. Finally, perform a recalibration of the range; by making adjustments, the simulated output of 4-20mA is made to match the external pressure signal source. This function is exactly the same as that of the zero adjustment (Z) and range adjustment (R) switches on the transmitter’s housing. Discussion on the issue: Some people believe that by using a HART handheld device, it is possible to change the range of an intelligent transmitter as well as adjust its zero and range settings, without the need for a pressure source. However, this approach cannot be considered calibration; it can only be referred to as \"setting the range\". True calibration requires using a standard pressure source to feed the transmitter. Adjusting the range (LRV, URV) without using a standard device is not calibration; adjusting the output (the transducer’s conversion circuit) while ignoring the input value (the pressure at the input transducer) is not proper calibration. Furthermore, the relationship between pressure, the pressure sensing element, the A/D conversion circuit, and the current output is not proportional; the purpose of calibration is to determine the relationship of changes among these three elements. Note: Only by calibrating both the input and output aspects (the pressure of the input transmitter, the A/D conversion circuit, and the loop current output circuit) can it be considered a true calibration. Any pressure transmitter, whether it is a 3051 or 1151 or any other brand or model, can be calibrated using a HART communicator.