Introduction The Smart Transmitter is a digital transmitter that can be used to communicate in both directions in the control room, on site, or anywhere in the same control loop, using a handheld communicator or other host that adheres to an associated protocol. At the same time, it also has some advanced features, such as the operator does not need to go to the scene, as long as in the operating room through the handheld communicator or DCS operating station keyboard, you can easily set and modify the various parameters of the field smart transmitter Or failure inspection, greatly reducing the labor intensity of workers, but also to facilitate the process of production. Smart transmitters have been rapidly promoted in petrochemical companies. However, some problems have also been encountered in the use of smart transmitters and instrument maintenance. Practical work has taken practical measures to solve them, and better results have been achieved. effect.
1. Problems in the application of smart transmitter 1.1 Application of EJA smart transmitter The EJA smart transmitter is a product of Yokogawa Electric Corporation in Japan. It was the first to adopt a digital single crystal silicon resonant sensor. The sensor outputs a pair of differential digital signals to directly eliminate external interference. An EJA118w double-flange level transmitter was used on the site of the utility project. The control room was powered by a 24VDC power supply. The signal was introduced into the conventional regulator to form a conventional control loop and a series connection was made in the measurement loop. Logger, a high-level (H) limit alarm setter and a low-level (L) limit alarm setter. EJA smart transmitter application circuit shown in Figure 1.
Before installation, the BT200 Communicator using the BRAIN protocol verified the transmitters, lines, and other instruments in the loop and showed that everything was working. However, the smart transmitter was installed on the site, and the intelligent transmitter was found to be unstable when put into use. When the liquid level is below 85%, the control circuit can still regulate normally; but when the liquid level exceeds 85%, the water tank overflows on site, the regulator liquid level indicator fluctuates at 80%, and the loop current no longer follows the measured parameter. As the value increases, the transmitter has failed. Check with BT200 communicator. Diagnostic information is communication failure. So we tried to delete the recorder and found that communication with the BT200 returned to normal and the smart transmitter's operation returned to normal, even if the loop current reached or exceeded 20mA. Based on this, we judged that the recorder caused the smart transmitter to not work properly, but after checking it again, it was found that the recorder was also good.
It can be seen that deleting the recorder only reduces the load resistance of the loop, and the power supply of the entire loop and the connection sequence of the instrument have not changed. The reduction of the load resistance means that the voltage supply of the transmitter itself increases. After analysis, it can be seen that the power supply voltage required by the EJA smart transmitter must be greater than 10.5V, and the loop power supply voltage and load resistance must satisfy R=(U-10.5)/0.0236. The relationship between the supply voltage and load resistance is shown in Figure 2.
In Figure 2: the shaded area is the communicative range of the BT200 and the transmitter. When the power supply voltage is 24V, the maximum external load is 570Ω. The transmitter's supply voltage must be greater than 16.4V and the load resistance must be greater than 25Ω for the BT200 to communicate with the transmitter. The on-site measurement line resistance is about 15Ω and the resistance of each load is 25Ω.
When the level exceeds 85%, the transmitter's supply voltage is:
24-16×85%×(250+250+250+250+15)=10.2V<10.5V(l)
It can be seen that to make the transmitter work properly, the key is to increase its voltage so that it is greater than 10.5V. Increasing the voltage can be solved by reducing the load resistance of the loop. Since the loop load resistance is fixed, only the voltage of the regulated power supply is increased. Finally adjust the voltage of the regulated power supply to 30V. The transmitter is stable and the communication is normal.
1.2 Application of ST300 Smart Transmitter In the process of transforming the DCS of the device, we used DCS and ST3000 smart transmitters from Honeywell, USA. According to the requirement of intrinsically safe explosion protection, the P+F type safety barrier was selected. The smart transmitter is connected to the safety barrier with a two-conductor shielded cable, and then connected to the terminal assembly FTA connected to the AI ​​card of the DCS via the safety barrier. ST3000 smart transmitter and DCS connection circuit wiring shown in Figure 3.
The wiring shown in Figure 3 supports 4-20mA analog and digital signal transmission [4]. After each smart transmitter was verified and installed on the site, the smart transmitter was found to be unstable during the joint school, but the hardware such as the inspection line, FTA, and safety barrier was normal. When the measured parameter is large, the loop current does not increase with the increase of the measured parameter value, and the transmitter fails. At this time, the SFC communicator following the DE protocol checks that the diagnostic information is HIRES/LOWVOLT. Indicates that the loop load resistance is too high or the transmitter supply voltage is too low. After trying to remove the safety barrier, the smart transmitter's operation returned to normal, and it can work even if the loop current reaches or exceeds 20 mA. After measurement, the line resistance is about 15Ω, the FTA signal sampling resistance is 250Ω, the current limiting resistance is 145Ω, and the safety gate resistance is about 330Ω, so in the loop, the load resistance is 740Ω.
ST000 smart transmitter voltage and resistance as shown in Figure 4. Load resistance R = (U-10.8)/0.0218, supply voltage U = 24VDC, the maximum load resistance required by the transmitter must be a total of 605.5Ω, apparently 740Ω exceeds the rated 605.5Ω resistance. Since it is no longer possible to increase the output voltage of the FTA, it is difficult to reduce the wire resistance and the FTA sampling resistance, and the safety barrier is set from a safety point of view and cannot be arbitrarily cancelled. Therefore, only by reducing the loop load resistance can the communication of the transmitter be satisfied. And use requirements.
By consulting Honeywell's DCS user manual, it can be seen that the 145Ω resistor acts as a current limiting protector in the measurement transmission loop. When the 145Ω current limiting resistor on the FTA is soldered with a soldering iron, the soldering copper wire is used for short circuit processing, and the safe operation of the FTA will not be affected in this loop, and the transmitter operation will return to normal after the implementation [2].
As can be seen from Figure 4, the ST3000 smart transmitter circuit starts with a basic supply voltage greater than 10.8V. When the supply voltage is 16.28V, the loop load resistance cannot exceed 250Ω and the transmitter can work normally.
The shaded part is the communicable range of the intelligent terminal and transmitter of the Honeywell DE communication protocol. There must be at least 250 Ω of loop load resistance in the loop. The transmitter's own supply voltage must be greater than 16.28 VDC, otherwise the smart terminal and transmitter cannot Normal communication.
2. Problem analysis in smart transmitter application: 0px; PADDING-LEFT: 0px; PADDING-BOTTOM: 0px; MARGIN: 20px0px0px; COLOR: rgb(0, 0, 0); PADDING-TOP: 0px; To analyze the problem of instrument power supply and impedance matching in smart transmitter applications, you first need to understand the basic working principle of a smart transmitter (using EJA as an example).EJA smart transmitter is composed of two silicon single crystal resonant sensors. The H-shaped vibration beam converts the differential pressure and pressure signals into frequency signals and sends them to the pulse counter. The difference in frequency is then directly transmitted to the CPU for signal processing. The D/A converter converts the signal to the input signal. -20mADC output signal, and superimposes a BRAIN/HART digital signal on the analog signal for communication.The built-in characteristic correction memory in the capsule box stores the ambient temperature and static pressure of the sensor, and the input/output characteristic corrects the data calculated by the CPU[7] Through the I / O port and external devices (such as hand-held intelligent terminal BT200 or BT275 and DCS with communication I / O card) to communicate data in digital communication, digital signal superimposed on the 4-20mA signal line, the pair -20mA signal does not generate any Disturbance [6].
The actual application of intelligent transmitters in the field, the most commonly encountered is the instrument power supply and impedance matching problems, in addition to EJA and ST3000 smart transmitters, other smart transmitters also have the same problem. For example, Rosemount's 3051 smart transmitter's maximum load resistance and supply voltage must also meet the corresponding relationship as shown in Figure 5, that is R = 43.5 × (U-10.5), also requires that the ripple of the DC power supply should be less than 2% for Transmitters with CSA certification standards cannot exceed 42.4V. It can be seen that smart transmitters all have strict requirements on the minimum operating voltage amplitude and load resistance, and require special attention in applications.
3. Concluding remarks In the process of use and maintenance, we must carefully read the data of smart transmitters and DCS systems; the technical requirements for the normal operation of field instruments and DCS systems must be discussed in depth; combined with the actual work, instrument engineering technology should be used. The wisdom of the personnel, dealing with the power supply and impedance matching of the smart transmitter, in order to improve the instrument maintenance level, promote the use of smart transmitters, and also create conditions for improving the automation level of petrochemical production.
1. Problems in the application of smart transmitter 1.1 Application of EJA smart transmitter The EJA smart transmitter is a product of Yokogawa Electric Corporation in Japan. It was the first to adopt a digital single crystal silicon resonant sensor. The sensor outputs a pair of differential digital signals to directly eliminate external interference. An EJA118w double-flange level transmitter was used on the site of the utility project. The control room was powered by a 24VDC power supply. The signal was introduced into the conventional regulator to form a conventional control loop and a series connection was made in the measurement loop. Logger, a high-level (H) limit alarm setter and a low-level (L) limit alarm setter. EJA smart transmitter application circuit shown in Figure 1.
Before installation, the BT200 Communicator using the BRAIN protocol verified the transmitters, lines, and other instruments in the loop and showed that everything was working. However, the smart transmitter was installed on the site, and the intelligent transmitter was found to be unstable when put into use. When the liquid level is below 85%, the control circuit can still regulate normally; but when the liquid level exceeds 85%, the water tank overflows on site, the regulator liquid level indicator fluctuates at 80%, and the loop current no longer follows the measured parameter. As the value increases, the transmitter has failed. Check with BT200 communicator. Diagnostic information is communication failure. So we tried to delete the recorder and found that communication with the BT200 returned to normal and the smart transmitter's operation returned to normal, even if the loop current reached or exceeded 20mA. Based on this, we judged that the recorder caused the smart transmitter to not work properly, but after checking it again, it was found that the recorder was also good.
It can be seen that deleting the recorder only reduces the load resistance of the loop, and the power supply of the entire loop and the connection sequence of the instrument have not changed. The reduction of the load resistance means that the voltage supply of the transmitter itself increases. After analysis, it can be seen that the power supply voltage required by the EJA smart transmitter must be greater than 10.5V, and the loop power supply voltage and load resistance must satisfy R=(U-10.5)/0.0236. The relationship between the supply voltage and load resistance is shown in Figure 2.
In Figure 2: the shaded area is the communicative range of the BT200 and the transmitter. When the power supply voltage is 24V, the maximum external load is 570Ω. The transmitter's supply voltage must be greater than 16.4V and the load resistance must be greater than 25Ω for the BT200 to communicate with the transmitter. The on-site measurement line resistance is about 15Ω and the resistance of each load is 25Ω.
When the level exceeds 85%, the transmitter's supply voltage is:
24-16×85%×(250+250+250+250+15)=10.2V<10.5V(l)
It can be seen that to make the transmitter work properly, the key is to increase its voltage so that it is greater than 10.5V. Increasing the voltage can be solved by reducing the load resistance of the loop. Since the loop load resistance is fixed, only the voltage of the regulated power supply is increased. Finally adjust the voltage of the regulated power supply to 30V. The transmitter is stable and the communication is normal.
1.2 Application of ST300 Smart Transmitter In the process of transforming the DCS of the device, we used DCS and ST3000 smart transmitters from Honeywell, USA. According to the requirement of intrinsically safe explosion protection, the P+F type safety barrier was selected. The smart transmitter is connected to the safety barrier with a two-conductor shielded cable, and then connected to the terminal assembly FTA connected to the AI ​​card of the DCS via the safety barrier. ST3000 smart transmitter and DCS connection circuit wiring shown in Figure 3.
The wiring shown in Figure 3 supports 4-20mA analog and digital signal transmission [4]. After each smart transmitter was verified and installed on the site, the smart transmitter was found to be unstable during the joint school, but the hardware such as the inspection line, FTA, and safety barrier was normal. When the measured parameter is large, the loop current does not increase with the increase of the measured parameter value, and the transmitter fails. At this time, the SFC communicator following the DE protocol checks that the diagnostic information is HIRES/LOWVOLT. Indicates that the loop load resistance is too high or the transmitter supply voltage is too low. After trying to remove the safety barrier, the smart transmitter's operation returned to normal, and it can work even if the loop current reaches or exceeds 20 mA. After measurement, the line resistance is about 15Ω, the FTA signal sampling resistance is 250Ω, the current limiting resistance is 145Ω, and the safety gate resistance is about 330Ω, so in the loop, the load resistance is 740Ω.
ST000 smart transmitter voltage and resistance as shown in Figure 4. Load resistance R = (U-10.8)/0.0218, supply voltage U = 24VDC, the maximum load resistance required by the transmitter must be a total of 605.5Ω, apparently 740Ω exceeds the rated 605.5Ω resistance. Since it is no longer possible to increase the output voltage of the FTA, it is difficult to reduce the wire resistance and the FTA sampling resistance, and the safety barrier is set from a safety point of view and cannot be arbitrarily cancelled. Therefore, only by reducing the loop load resistance can the communication of the transmitter be satisfied. And use requirements.
By consulting Honeywell's DCS user manual, it can be seen that the 145Ω resistor acts as a current limiting protector in the measurement transmission loop. When the 145Ω current limiting resistor on the FTA is soldered with a soldering iron, the soldering copper wire is used for short circuit processing, and the safe operation of the FTA will not be affected in this loop, and the transmitter operation will return to normal after the implementation [2].
As can be seen from Figure 4, the ST3000 smart transmitter circuit starts with a basic supply voltage greater than 10.8V. When the supply voltage is 16.28V, the loop load resistance cannot exceed 250Ω and the transmitter can work normally.
The shaded part is the communicable range of the intelligent terminal and transmitter of the Honeywell DE communication protocol. There must be at least 250 Ω of loop load resistance in the loop. The transmitter's own supply voltage must be greater than 16.28 VDC, otherwise the smart terminal and transmitter cannot Normal communication.
2. Problem analysis in smart transmitter application: 0px; PADDING-LEFT: 0px; PADDING-BOTTOM: 0px; MARGIN: 20px0px0px; COLOR: rgb(0, 0, 0); PADDING-TOP: 0px; To analyze the problem of instrument power supply and impedance matching in smart transmitter applications, you first need to understand the basic working principle of a smart transmitter (using EJA as an example).EJA smart transmitter is composed of two silicon single crystal resonant sensors. The H-shaped vibration beam converts the differential pressure and pressure signals into frequency signals and sends them to the pulse counter. The difference in frequency is then directly transmitted to the CPU for signal processing. The D/A converter converts the signal to the input signal. -20mADC output signal, and superimposes a BRAIN/HART digital signal on the analog signal for communication.The built-in characteristic correction memory in the capsule box stores the ambient temperature and static pressure of the sensor, and the input/output characteristic corrects the data calculated by the CPU[7] Through the I / O port and external devices (such as hand-held intelligent terminal BT200 or BT275 and DCS with communication I / O card) to communicate data in digital communication, digital signal superimposed on the 4-20mA signal line, the pair -20mA signal does not generate any Disturbance [6].
The actual application of intelligent transmitters in the field, the most commonly encountered is the instrument power supply and impedance matching problems, in addition to EJA and ST3000 smart transmitters, other smart transmitters also have the same problem. For example, Rosemount's 3051 smart transmitter's maximum load resistance and supply voltage must also meet the corresponding relationship as shown in Figure 5, that is R = 43.5 × (U-10.5), also requires that the ripple of the DC power supply should be less than 2% for Transmitters with CSA certification standards cannot exceed 42.4V. It can be seen that smart transmitters all have strict requirements on the minimum operating voltage amplitude and load resistance, and require special attention in applications.
3. Concluding remarks In the process of use and maintenance, we must carefully read the data of smart transmitters and DCS systems; the technical requirements for the normal operation of field instruments and DCS systems must be discussed in depth; combined with the actual work, instrument engineering technology should be used. The wisdom of the personnel, dealing with the power supply and impedance matching of the smart transmitter, in order to improve the instrument maintenance level, promote the use of smart transmitters, and also create conditions for improving the automation level of petrochemical production.
Spun Rayon Fabric,Print Fabric,Crepe Yoryu Fabric,100% Viscose Fabric
Shaoxing MingFang Textile Co., Ltd , https://www.printingsfabrics.com