【Daily Question 20090221】Double-flange differential pressure transmitter

We use Rosemount differential pressure transmitters, and when selecting these products it is essential to ensure that welded pipe fittings are provided at the inlet and outlet ports, which facilitates their use by users

The EJA intelligent dual-flange differential pressure transmitter is a product of Yokogawa Electric Corporation in Japan. The main problems I encountered were: 1. No display； 2. The operation is not normal ； 3. Abnormal communication ； 1. Display issues mainly arise from over-range use, which leads to display problems; it is recommended to consider the maximum operating range at the design stage to meet usage requirements ； 2. Abnormal operation is mainly due to the high value of the terminal resistance of the associated Zener safety barrier, which results in a low operating voltage for the transmitter and prevents it from functioning; it is recommended to use an isolated safety barrier. 3. Abnormal communication is primarily caused by improper setting of the communication parameters. Read the instructions carefully.

I only looked at how to choose the model and brand. . . Yes? ? Differential pressure transmitters are selected based on the following factors: (1) measurement range, required accuracy, and measurement functions ； (2) The environment surrounding the measuring instruments, such as the industrial environment in the petrochemical industry, features the presence of flammable (toxic) and explosive atmospheres as well as high ambient temperatures ； (3) The physicochemical properties and state of the medium under test, such as conditions involving strong acids, strong bases, viscosity, tendency to solidify or crystallize, and vaporization ； (4) Changes in operating conditions, such as changes in medium temperature, pressure, and concentration. Sometimes it is also necessary to take into account the changes in gas and liquid concentrations and densities from the time of starting the process until the parameters reach normal production levels ； (5) The structure, shape, and dimensions of the container under test, as well as the equipment and accessories inside it and various inlet and outlet pipes, must all be taken into consideration, such as towers, solution tanks, reactors, boiler drums, vertical tanks, spherical tanks, etc ； (6) Other requirements, such as environmental protection and hygiene requirements ； (7) A unified approach should be adopted in the selection of process instruments, with an effort to minimize the variety of models and specifications as well as the amount of spare parts, to facilitate management ； (8) Specific requirements of the process patent holder. (9) Actual process conditions: ① Consider which category of equipment the object under test belongs to. Such as tanks and containers: tanks have a smaller volume, so the measurement range is not very large, while containers have a larger volume, resulting in a potentially larger measurement range ； ② Depending on the physical and chemical properties of the medium as well as its level of cleanliness, conventional differential pressure transmitters and float-type level transmitters are the preferred choices; in addition, it is necessary to select the material used for the parts that come into contact with the medium ； ③ For some media such as suspended solids and foam, a single-flange differential pressure transmitter can be used. For those that are prone to precipitation and crystallization, plug-in double-flange differential pressure transmitters are used ； ④ For the level of highly viscous fluids as well as the level in high-pressure equipment, where it is not possible to make openings in the equipment, radio level gauges can be used for measurement ； ⑤ In addition to issues with measurement methods and technology, there are also problems related to investment in instruments. In summary, the selection of a transmitter should be technically feasible, economically reasonable, and convenient for management.

Found it; it’s the same as the one upstairs! Differential pressure transmitters are selected based on the following factors: (1) measurement range, required accuracy, and measurement functions ； (2) The environment surrounding the measuring instruments, such as the industrial environment in the petrochemical industry, features the presence of flammable (toxic) and explosive atmospheres as well as high ambient temperatures ； (3) The physicochemical properties and state of the medium under test, such as conditions involving strong acids, strong bases, viscosity, tendency to solidify or crystallize, and vaporization ； (4) Changes in operating conditions, such as changes in medium temperature, pressure, and concentration. Sometimes it is also necessary to take into account the changes in gas and liquid concentrations and densities from the time of starting the process until the parameters reach normal production levels ； (5) The structure, shape, and dimensions of the container under test, as well as the equipment and accessories inside it and various inlet and outlet pipes, must all be taken into consideration, such as towers, solution tanks, reactors, boiler drums, vertical tanks, spherical tanks, etc ； (6) Other requirements, such as environmental protection and hygiene requirements ； (7) A unified approach should be adopted in the selection of process instruments, with an effort to minimize the variety of models and specifications as well as the amount of spare parts, to facilitate management ； (8) Specific requirements of the process patent holder. (9) Actual process conditions: ① Consider which category of equipment the object under test belongs to. Such as tanks and containers: tanks have a smaller volume, so the measurement range is not very large, while containers have a larger volume, resulting in a potentially larger measurement range ； ② Depending on the physical and chemical properties of the medium as well as its level of cleanliness, conventional differential pressure transmitters and float-type level transmitters are the preferred choices; in addition, it is necessary to select the material used for the parts that come into contact with the medium ； ③ For some media such as suspended solids and foam, a single-flange differential pressure transmitter can be used. For those that are prone to precipitation and crystallization, plug-in double-flange differential pressure transmitters are used ； ④ For the level of highly viscous fluids as well as the level in high-pressure equipment, where it is not possible to make openings in the equipment, radio level gauges can be used for measurement ； ⑤ In addition to issues with measurement methods and technology, there are also problems related to investment in instruments. In summary, the selection of a transmitter should be technically feasible, economically reasonable, and convenient for management.

No, that’s correct; this is a common issue

We use Rossmont differential pressure transmitters quite often

Pay attention to temperature, materials, and installation method

Differential pressure transmitters are selected based on the following factors: (1) measurement range, required accuracy, and measurement functions； (2) The environment surrounding the measuring instruments, such as the industrial environment in the petrochemical industry, features the presence of flammable (toxic) and explosive atmospheres as well as high ambient temperatures ； (3) The physicochemical properties and state of the medium under test, such as conditions involving strong acids, strong bases, viscosity, tendency to solidify or crystallize, and vaporization ； (4) Changes in operating conditions, such as changes in medium temperature, pressure, and concentration. Sometimes it is also necessary to take into account the changes in gas and liquid concentrations and densities from the time of starting the process until the parameters reach normal production levels ； (5) The structure, shape, and dimensions of the container under test, as well as the equipment and accessories inside it and various inlet and outlet pipes, must all be taken into consideration, such as towers, solution tanks, reactors, boiler drums, vertical tanks, spherical tanks, etc ；

I won’t go into too much detail regarding the rules and guidelines for choosing double-flange transmitters; fellow users can take a look at the posts above. I’ll just share my own experience based on practical use: First, double-flange transmitters have a relatively large measurement range. Therefore, when devices that require a large measurement range are needed, double-flange transmitters are generally used for ranges of over 2 meters. Of course, the specific situation also matters – they are often used in towers and reactors, while radar transmitters are more commonly used in storage tanks and similar applications. II. When selecting double flanges specifically, there are several points to keep in mind: 1. Determine the length of the double-flange capillary based on the location of the pressure tapping point and the installation position of the double flanges. 2. Determine the double-flange displacement based on the distance between the pressure tapping points; everyone is familiar with the formula for this – displacement = ρgh, where ρ is the density of the filling fluid and h is the distance between the pressure tapping points. In the case of level measurement, ρ represents the difference in density between the two fluids. 3. Select an appropriate filler based on the applicable ambient temperature; for example, low-temperature silicone oil should be used in cold regions. 4. Double flanges generally require short pipes to facilitate future maintenance; these short pipes can be filled with isolation fluid for flushing purposes. They can also be equipped with matching flanges suitable for the double flanges, which makes installation easier. Since the double flanges from brands such as Rosemount and EJA do not have flange connections that comply with the HG standard, the ANSI standard is usually used instead. The above are several selection issues encountered during the design process, for your reference only.

We use those from Tianjin Sos. The knowledge for selection is basically the same as that of the above-mentioned individuals.

We use Rosemont’s and PDS here

Our company uses Rosemount differential pressure transmitters.

1. Typical faults of the EJA intelligent double-flange differential pressure transmitter. The EJA intelligent double-flange differential pressure transmitter is a product of Yokogawa Electric Corporation in Japan. At Fushun Oil Plant No. 1, this product is widely used for measuring the liquid level in towers, tanks, and containers. During use, numerous failures occurred due to improper usage methods, which severely affected the proper operation of the instrument. The author conducted extensive analysis and research on actual failures and found that they mainly fall into the following three categories: ① No display value caused by measurement exceeding limits. ② It does not match the safety barrier, resulting in no measurement signal or a low signal level in the circuit. ③ Unable to communicate with DCS. 2. Methods for dealing with typical faults 2.1 Methods for handling cases of excessive measurements Through analysis, it has been found that such faults are usually related to the following factors: ① Improper operation of the instruments. Taking the LICA-1201 level control system of the toluene unit at Fushun Petroleum Plant No. 1 as an example, as shown in Figure 1, the instrument may indicate an excessive level if it operates at a high level (above 100%) all the time, or if it operates at a low level (below 5%) all the time. Therefore, process operators are required to be able to correctly determine whether it is an instrument failure or improper process operation based on the process flow and process control requirements. Therefore, close cooperation between process personnel and instrument maintenance staff is necessary to ensure that the process medium remains within the range that the instruments can measure, thereby preventing operators from mistaking it for an instrument failure. Figure 1: Process diagram of the C-101 level control system. ② Improper selection of instrument ranges: When checking the measurement ranges of the EJA intelligent double-flange transmitters used in the same benzene processing unit at this plant, design and calculation errors were found in these transmitter ranges. For example, when checking the ranges of transmitters such as LICA-1201 on the DCS engineer station, it was observed that the double-flange range settings had not been adjusted, which is a major cause of inaccurate measurements and range violations, as shown in Figure 2. . Figure 2: Range calculation parameters for Tower 101. The original design specified a range of 0~19.71 kPa with no range shift; as a result, measurement values fell outside the instrument’s range, leading to measurement out-of-limit conditions. In fact, the range of this instrument should be calculated using the following method: Given: the range that the instrument can measure, the specific gravity of the medium, and the specific gravity of the capillary silicone oil. Find the instrument range. Solution method: The range of the gauge refers to the pressure exerted on the level gauge when the liquid level rises from its lowest point to its highest point. Therefore, the range is as follows: When the liquid level is at its lowest, the pressures in the positive and negative chambers of the level gauge are: The displacement of the level gauge is given by: = –2.65 = –2.65 × 1.07 × 9.81 = –27.82 kPa. Since P+ > P-, the displacement is negative. After adjusting the range according to the above calculations, the instrument operates normally. Therefore, only by using the correct calculation method and referencing the migration amount can the accuracy of the instrument’s range be ensured. 2.2 Inaccurate readings and no output from the instruments due to an incompatible safety gate: Since smart transmitters require a safety gate that is compatible with them, using a safety gate that does not have the necessary license for use with such transmitters leads to various problems. The main issues include: ① Excessive voltage drop across the safety gate, resulting in a circuit voltage below 16.4V; this insufficient power supply prevents the transmitter from functioning, as shown in Figure 3. . Figure 3 shows the relationship between the supply voltage and load resistance of the EJA intelligent transmitter. The dashed area indicates the range within which the instrument can operate properly; the external resistance should be between 250 and 600. Sometimes the loop resistance measurement is >700, which causes measurement errors and may even prevent the transmitter from functioning. ② The safety barrier lacks an intrinsically safe ground, resulting in large common-mode interference signals that cause the intelligent transmitter to malfunction. Taking the Z787H model from P+F Company, which is used in benzene plants on site, as an example, the correct wiring is shown in Figure 4; however, it has been found that sometimes the safety barrier is not grounded, resulting in no output from the transmitter. . Figure 4: Connection method of the safety barrier to the intelligent transmitter and DCS. ③ Although there is compatibility verification in the instrument room, an intrinsically safe safety barrier was chosen in situations where a transformer-isolated safety barrier would have been more appropriate; as a result, the supply voltage to the instruments was insufficient, and there was no separate power supply, which led to poor interference resistance and prevented the transmitters from functioning properly. Therefore, selecting a suitable safety barrier that has been tested is also a necessary condition to ensure the proper operation of the transmitter. 3. Communication failures with the DCS: Generally, the DCS can be used to manage, configure, install, and download data from all smart transmitters. Among instrument failures, most are caused by improper parameter settings within the instruments, and on the DCS operator station, parameter configuration for intelligent transmitters is carried out via communication. Therefore, their communication with DCS is extremely important. Most of the EJA transmitters used in this plant communicate with the CENTUM-CS system, and its ICS operation station can communicate with the FCS field control stations and field intelligent transmitters to configure parameters such as the transmitters’ measurement values, range limits, self-diagnosis information, and tag numbers, as shown in Figure 5. In actual production, if there is a failure in the communication between the transmitter and the DCS, it causes many difficulties for instrument maintenance personnel in checking instrument parameters and identifying instrument faults; in some cases, it even prevents the transmitter from functioning properly. . Figure 5 Schematic diagram of communication between DCS and intelligent transmitters. Last edited by *anpangpang on 2009-2-21 21:25]