Typical Fault Handling of Double Flange Differential Pressure Transmitter in Paper Industry

Microprocessor-based field smart transmitters have features such as high accuracy, high reliability, good stability, wide measurement range, and large turndown ratio compared to conventional transmitters. Both DCS systems with the same communication protocol or field communication controllers and setters are used for data communication functions, and various parameters of smart transmitters are modified, set, remotely tuned, entered into a dialogue, and online. Monitoring and other functions. Like all smart meters, smart transmitters also have a more complete self-diagnostic function.

1 Typical Fault of EJA Smart Dual Flange Differential Pressure Transmitter

EJA intelligent double-flange differential pressure transmitter is a product of Japan Yokogawa Electric Co., Ltd. In Fushun Oil Plant 1, this product is used for a large number of level measurement of towers, tanks, and containers. In the process of use, due to improper use of methods caused more failures, seriously affecting the normal use of the instrument. The author did a lot of analysis and research on actual faults and found that there are mainly three types of faults:

1 Measured without display due to overrun.

2 It is not matched with the safety barrier, causing the loop to have no measurement signal or the signal is low.

3 Cannot communicate with DCS.

2 Typical Troubleshooting Methods

2.1 How to Measure Out-of-limits

Through research and analysis, it was found that such failures are usually related to the following factors:

1 Improper use of instrument operation

Take Fushun Petroleum No.1 Ketone Benzene Device C-101 Liquid Level Control System (LICA-1201) as an example. As shown in Figure 1, the instrument is always running at a high level (100% or more), or the meter is always at a low level. (5% or less) operation may cause the meter to indicate overrun. Therefore, it is required that the process operator should correctly determine whether the instrument is faulty or the process is not properly handled according to the process flow and process control requirements. Therefore, the technicians and instrument maintenance personnel are required to cooperate closely to ensure that the process media can be measured within the range of the meter and avoid the operator from mistakenly thinking that the instrument is faulty.

Figure 1 C-101 level control system process map

2 Improper selection of meter range

When measuring the range of the EJA intelligent dual flange transmitter in the Ketone Benzene plant, it was found that there was a design calculation error in the transmitter range. For example, the transmitters such as LICA-1201 were tested at the DCS engineering station to check their range. At that time, it was found that there was no migration in the double flange range, which was an important reason for the inaccurate measurement and over-limitation of the meter, as shown in Figure 2.

Figure 2 Tower 101 Range Calculation Parameter Map

The original design used a range of 0~19.71kPa, no range migration, so the measurement results outside the range of the instrument, the measurement overrun conditions. In fact, this instrument should be calculated by the following method:

Known: meter measurable range , Medium weight , capillary silicone oil specific gravity .

Find the instrument range.

Solving method: The range of the instrument is the pressure on the liquid gauge when the liquid level rises from the lowest to the highest. for:

When the liquid level is the lowest, the forces of the positive and negative pressure chambers of the liquid level gauge are:

Level meter migration is:

=-2.65 =-2.65×1.07×9.81

= -27.82kPa

P+>P-, it is a negative migration.

After calculating the range according to the above calculation, the instrument operation is normal. Therefore, the accuracy of the instrument's range can only be guaranteed if it is calculated in accordance with the correct calculation method and the referenced migration amount.

2.2 The safety barrier is not matched and causes the meter to have no output and the measurement is not accurate.

Because smart transmitters require the use of an accompanying safety barrier, the majority of problems arise when using a safety barrier that has not been approved for use with smart transmitters. The major faults are:

1 The voltage drop of the safety barrier is too large, the entire loop voltage is lower than 16.4V, the transmitter power supply is insufficient, and the loop cannot work, as shown in Figure 3.

Figure 3 Relationship between supply voltage and load resistance of EJA smart transmitter

The dashed area indicates the normal range of operation of the meter. The external resistance should be at 250 ~600 between. Sometimes measuring loop resistance >700 This causes measurement deviations and even the transmitter does not work.

2 The safety barrier is not intrinsically safe, causing large common-mode interference signals and causing the smart transmitter to malfunction. Take the Z787H of the P+F company that uses the ketobenzene device as an example. The correct connection is shown in Figure 4, but it was found that sometimes the safety barrier is not grounded, making the transmitter output-free.

Fig. 4 Connection method of safety barrier and intelligent transmitter and DCS

3 Although there is compatible forensics between instruments, but in the case of transformer isolation barriers should be selected, but intrinsically safe barrier is selected, making the instrument supply voltage is insufficient, no independent power supply and the formation of anti-interference ability is poor, resulting in transmission The device does not work properly. Therefore, the selection of a suitable fortified safety barrier is also a necessary condition for the transmitter to work properly.

3 Communication failure with the DCS

In general, the task of managing, configuring, uploading, and downloading all smart transmitters can be accomplished through DCS. In the fault of the instrument, most of the faults are caused by improper settings of the internal parameters of the instrument. On the DCS operation station, the parameters of the smart transmitter are configured through communication. Therefore, their communication with the DCS is extremely important. Most of the EJA transmitters used in this plant communicate with the CENTUM-CS system. The ICS operation station can communicate with the field smart transmitter through the FCS field control station. The measured value, range, self-diagnosis information and bits of the transmitter are used. Numbers, etc. are configured as shown in Figure 5. In actual production, if the transmitter fails to communicate with the DCS, it will cause the instrument maintenance personnel to check the instrument parameters and the instrument failure. This will cause a lot of inconvenience and even make the transmitter unable to work properly.

Figure 5 Communication between DCS and smart transmitter

4 Conclusion

EJA intelligent dual-flange differential pressure transmitter is a more advanced intelligent instrument, with strong functions and high reliability. As long as the proper maintenance is applied, it can keep them in normal operation for a long time, thus effectively ensuring the measurement accuracy of the entire control system and reliability.