The intelligent differential pressure transmitter is an intelligent detection instrument formed by adding a microprocessor circuit based on a common differential pressure sensor. It has a series of advantages such as stable performance, good reliability and high measurement accuracy. The intelligent differential pressure transmitterhas an automatic compensation function for temperature and static pressure. When the temperature is detected, the nonlinearity can be automatically corrected. It has two digital and analog output modes, which can realize two-way data communication, and can also realize remote communication. Through the field communicator, the transmitter has various functions such as self-correction, automatic compensation, self-diagnosis and error mode alarm. Therefore, the transmitter has been widely used in the petroleum and chemical industries. Usually to ensure that the transmitter is stable and working properly, we need to verify it before installation or after long-term use. This article takes Rosemount 3051 differential pressure transmitter as an example to briefly introduce the inspection method of differential pressure transmitter.
In the calibration process, the intelligent differential pressure transmitter requires the instrument personnel to skillfully install the transmitter and correctly connect the instrument circuit and the gas path. After the connection is properly energized, the basic parameters of the transmitter are configured and configured using the HART 475. The whole verification process is divided into the following aspects: equipment inspection and tool inventory, transmitter installation, instrument loop and pneumatic connection, correct connection of the handheld device, parameter setting and configuration, verification data record and Processing, safe and civilized operations, etc.
In the calibration process of the intelligent differential pressure transmitter, we need to use the transmitter verification training system. The whole system consists of pneumatic signal generator, digital multimeter, regulated power supply, standard resistance box, transmitter mounting bracket, pipe connection joint and accessories. The specific model specifications and quantities are shown in the following table:
In addition to the above equipment, we also need a Rosemount 3051 intelligent differential pressure transmitter, a HART 475 handheld device, and tools such as wrenches and screwdrivers.
For field instrument maintenance workers, the verification of differential pressure transmitters is a must-have skill. Our company also included the verification of the intelligent differential pressure transmitter in the assessment content of the professional maintenance appraisal of the instrument maintenance workers. The verification of the differential pressure transmitter is divided into the following steps:
3.1.1 Appliance inspection
Check that the signal generator, digital multimeter, regulated power supply, standard resistance box, pressure pump, hand-held device, tools and instrument connectors are complete.
3.1.2 Equipment adjustment
Regulated power supply voltage modulation (24 ± 0.5) VDC
The resistance box is adjusted between 250~500Ω
Signal generator power on preheat, set range
Power the digital multimeter and select the correct gear
3.2 Line connection
According to the positive pole of the 24V power supply, string the 250Ω resistor, then connect to the “+” of the transmitter signal terminal, and the “-” of the transmitter signal terminal to the “+” of the digital multimeter (or multimeter), the digital multimeter. The "-" of the (or multimeter) is connected to the negative of the 24V power supply, thus forming a closed loop. The line connection is shown in Figure 3.1:
3.3 parameter settings
In terms of parameter settings, we mainly use Emerson's HART 475 Communicator to parameterize the transmitter. It includes the input instrument's bit number, damping time, unit, zero point, range and linear or square selection of the transmitter. After setting these parameters, we need SEND so that all modified parameters will be valid.
3.4 Transmitter verification and data processing
After the entire instrument loop is connected and the power is turned on, the transmitter is verified by the 475 Communicator. First verify the zero point of the transmitter and then check the range. After the zero-point range is correct, the transmitter is calibrated up and down by 5 points, that is, 0 points, 25%, 50%, 75%, and 100% are taken in the selected measurement range, and relevant data is recorded. Then come to a conclusion.
In the process of verifying the transmitter, you need to fill in a series of information such as the bit number, range, transmitter model, accuracy grade, standard meter model and accuracy grade. This information can be obtained from the transmitter. Obtained on the nameplate of the standard watch. The actual measured value requires us to record truthfully during the calibration process, and calculate the error and the hysteresis based on the recorded value, and judge the conclusion based on the calculated result. Below I briefly introduce the calculation method of error and hysteresis.
The error we are talking about here is the ZUI large reference error.
The hysteresis we call is the ZUI large measurement difference. The hysteresis (also called the variation) refers to the large difference in ZUI between the two corresponding output values of the same input when the input amount rises or falls. We usually use the percentage of the output range to represent. The formula is as follows:
According to the recorded data, we can calculate the accuracy of the transmitter according to the above two formulas. If one of the actual error and the backlash is not met, it is considered unqualified. If it fails, we will recalculate its accuracy level.
4, The conclusion
The verification of the differential pressure transmitter is a detailed, cumbersome, and systematic project. The above is the overall procedure for the verification of the differential pressure transmitter. Each company may be slightly different, but the overall idea and steps are the same. The verification of the differential pressure transmitter is a required subject for the professional skill appraisal of our company's instrument maintenance workers. With the advancement of technology, the number of verifications of differential pressure transmitters is getting better and better, and the stability of use is getting better and better. However, the above verification process and the processing of data are still a basic skill of the instrument maintenance personnel working in the production line.
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