Yokogawa’s transmitter dual signal output

The 4-20mA signal is itself a current signal and can be connected in series. It should be noted, however, that the output resistance of each transmitter must not exceed a certain value; for example, the load resistance for EJA transmitters should generally be between 250 and 600 ohms. Typically, the load resistance of ROSEMOUNT is around 600 ohms, and it varies with the supply voltage. The specific relationship is: maximum loop resistance = 43.5 X (supply voltage – 10.5). Any value for the load resistance that exceeds this limit will result in abnormal output from the transmitter. These are just my personal opinions; I hope they can be helpful to you.

This is a summary of the typical fault handling methods for EJA differential pressure transmitters, compiled by me. It outlines detailed approaches to dealing with common faults in EJA intelligent double-flange differential pressure transmitters, based on their actual application scenarios. Practice has shown that only through proper use and maintenance can the long-term stable operation of the instruments be ensured. Introduction Compared to conventional transmitters, microprocessor-based field intelligent transmitters feature high precision, high reliability, good stability, a wide measurement range, and a large ratio of measurement ranges. It has the function of performing data communication with DCS systems or field communication controllers and setpoints that use the same communication protocol, as well as functions such as modifying and setting various parameters of intelligent transmitters, enabling remote tuning, interactive operation, and online monitoring. Like all smart meters, smart transmitters also have a fairly comprehensive self-diagnosis function. 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 malfunctions 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 a liquid level control system in one of our company’s purification units as an example, if the instrument operates at a high liquid level (above 100%) or at a low liquid level (below 5%), this can cause the instrument to indicate an excessive value. 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 engineers and instrument maintenance personnel 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. ② Improper selection of the instrument range: When checking the measurement ranges of the EJA intelligent double-flange transmitters in the devices, 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 did not shift, which is a major cause of inaccurate measurements and exceeding specified limits. This leads to measurement errors, and in some cases, the transmitters may even stop functioning. (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 gate is not grounded, resulting in no output from the transmitter. Connection methods of safety barriers to intelligent transmitters and DCSs: ③ Although there is compatibility certification available for instrument rooms, in situations where a transformer-isolated safety barrier should be used, an intrinsically safe safety barrier was chosen instead. This resulted in insufficient power supply voltage for the instruments, as well as a lack of an independent power source, leading to poor interference resistance and preventing 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 speaking, the DCS can be used to manage, configure, install, and download data from all intelligent transmitters. Among instrument failures, most are caused by improper setting of internal parameters of 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. 4. Conclusion The EJA intelligent differential pressure transmitter is a relatively advanced smart instrument with strong functions and high reliability. With proper operation and maintenance, it can remain in normal operation for a long time, thereby ensuring the measurement accuracy and reliability of the entire control system.

It is best not to use a series connection, as in such a configuration, if one instrument malfunctions and needs to be repaired, it is likely to affect the reception of signals from the other instrument. It is best to output two signals through a signal distributor and send them to the two receiving instruments respectively.

It can be used in less important situations where the impedance meets the requirements.

The older brother has a safety barrier with single input and dual output; there’s no need to save such a small amount of money.

I don’t know much about safety barriers; I just learned that there are ones with single input and multiple outputs. Thank you to the person who posted above.

If it’s just to save money by connecting things in series, you can give it a try and keep good records of the debugging process. It is recommended to use a distributor

Generally, the sampling resistor does not fail, so the malfunction of one circuit does not necessarily affect functionality.

It is recommended not to connect them in series; apart from load issues, a failure at any point in the circuit will cause both systems to receive invalid signals. A 1-to-2 signal splitter can be used.

1. This series connection is feasible, but since it is a series connection, if there is a break in the LOOP, both systems will be affected. 2. Use the isolation barrier to input 2 outputs. 3. There is another method: the transmitter is connected to a DCS, and the remaining AO channels in that DCS are used to transmit the signal to another system. This post was last edited by s1j2 on 2009-3-15 09:33]

The main areas where breaks occur are the field meters and field cables; problems are less likely to arise on the side of the indoor cabinet where the cables are properly connected. Adding a distributor does not prevent problems on the field side; on the contrary, the distributor itself is a point of failure. Therefore, series connection of cabinet rooms is feasible and reliable.