The temperature communication with the best accuracy, reliability, the minimum noise

The communication from temperature sensors to the control room should be designed to provide the maximum accessability, flexibility, reliability and accuracy. Traditionally considered the cheapest solution to generate serious consequences and hidden costs. Here, let's see how the intelligent transmitter and wireless communication appear on how to make better communication, lower installation and life cycle costs, and process performance improvement.

The most common process measurement of the number of sensors in the process factory is the temperature. The distillation tower may have four or more temperature sensors to find the best temperature control tower, and the fluidized bed reactor may choose 10 or more temperature sensors to handle hotspots. In the past, the cheapest hardware was used to transmit temperature to the control room without realizing the impact on measurement accuracy, noise and reliability.

In fact, the early distributed control system (DCS) eliminates the TC input card that can process 16 or 32 input cards by connecting thermocouple (TC) to eliminate the temperature The cost of transmitter is reasonable to a certain extent. Due to the offset of the 12 -bit width range input card and 10 O, the result of the introduction of a step -long step (simulated to digital converter noise) in the introduction of 0.35 O F is the difference between the disaster F or more due to the error due to sensors and the lead. Noise from electromagnetic interference is common. It is impossible to use a differential movement, and the PID gain must be reduced. The temperature error of the color spectrum and the reactor and the composition error caused by it causes the process performance and the product is not qualified. In many cases, adjust the temperature setting point to compensate the error and add a signal filter to reduce the noise of the total ring road dead area.

Signal transmission
In order to be useful for control, security, or monitoring, the temperature measurement signal must be transmitted from the measurement point to the control system of the process. The two most common ways are:

● The transmitter-a short distance between the sensor and the transmitter or directly connected to the transmitter, where the signal is converted into a number, 4-20 mA, or wireless signal. The conversion signal output is then transferred to the control system through the transmission line or wireless network.
● Direct connection -The wire of the sensor is connected to the entire distance of the control system. There is no signal conversion along the way.
The benefits of using the temperature transmitter instead of directly connected to the control system are:

● Provide a more stable signal-4-20 mA or digital signal output from the transmitter is more stable than a direct-connected sensor signal. Noise interference has less impact on 4–20 mA or digital signals.
● The measurement accuracy is the best -transmitter provides higher measurement accuracy than direct wiring. For example, the sensor can match the transmitter (matching the transmitter sensor), thereby improving the accuracy of temperature measurement. The temperature span can be reduced to the matching process of the matching process (it is of great significance for the old DCS with a 12 -bit input card).
● Lower installation and maintenance cost -transmitter installation is usually cheaper than direct connection sensors, because it can save wiring costs and installation (sensor lines, especially TC cables are relatively expensive). In addition, by enhancing the function and diagnosis of the transmitter, strong signals and accurate measurements can save time and money.
● Better process performance -higher accuracy and reliability and lower noise reduce process variability and increase production time.
It is recommended to use a transmitter instead of TC or RTD input cards. By matching calibration and non -linear compensation with sensors, reduced range, reducing noise, and providing diagnosis to greatly improve accuracy and maintainability.

The use of digital communication allows a single transmitter to measure multiple temperatures and return these measurements to the additional flexibility of the control system. There are some temperature equipment designed to use this function to provide four, eight or more capable temperatures that may be measured. The most common communication technology is standard protocols such as Hart & Reg; (including Wirelesshart ™).

The reliability, security and easy settings of

Wirelesshart (remarkable remote sensor) network, plus the battery life brought by new communication rules and PID enhancement, making wireless communication a good choice. Most of the temperature changes are very slow. The refresh time can be set to longer than other types, thereby extending the battery life. In addition, compared with other circuits, the noise amplitude and cycle in the temperature circuit are usually very small, unless there are two phases (for example, liquid and gas) or poor mixing (for example, poor uniformity -due to insufficient mixing, increased variability), increased variability), increased variability), and increased variability), increased variability). As a result, the number of abnormality triggered by noise is reduced, which also extends the battery life.

The advanced temperature communication of technology can reduce installation costs and reduce errors and noise. The emergence of a smart transmitter makes it more attractive to install the transmitter directly on the thermocouple sleeve . The combination of integrated installation and wireless options creates excellent opportunities for process performance improvement. This article provides some general guidance. For more detailed information, including the Formula for predicting eight measurement errors, see Greg McMillan's ISA book advanced temperature measurement and control, the second edition.

Install transmitter on -site
The on -site installation transmitter is the strongest of all transmitter types. Its solid shell can prevent corrosion and humidity. Some on -site installation transmitters install electronic components in dual -outdoor shells, which completely isolate them from the impact of humidity. The dual -chamber transmitter is the best design used in harsh environments. The on -site installation transmitter can be installed or remotely installed.

In the overall installation, the transmitter is directly installed on the thermal electric puppet sleeve through the threaded tube joint and pipe joint to easily disassemble the sensor. Because today's smart transmitters are extremely reliable and have a very low drift rate, the calibration interval is shortened to more than 5 years, so it can be remotely viewing the diagnosis and the calibration can be completed remotely. Therefore Demand. The overall installation of the transmitter reduces the installation cost and eliminates errors and noise introduced by the lead and additional terminals.

● Integrated installation -the transmitter is directly screwed on the sensor (directly installed on the American style [1/2 inch NPT] sensor, it is best to use the pipe joint).
● Remote installation-transmitter is installed on a pipe rack or other bracket near the sensor. When the measurement point cannot be close or the process is too bad, so that the transmitter cannot be directly installed at the top of the sensor, the preferred remote installation is preferred.
In the case of permission and temperature permission, the overall installation of the intelligent transmitter improves the measurement accuracy and reliability.

The use of integrated installation and wireless transmitter provides flexibility and portability, which can be used to monitor the operating efficiency of the unit, and find the most representative and sensitive measurement position at the least process of the dead area time. . As long as there is a pipeline connection or equipment nozzle, and the vision of the wireless transmitter that is used at the Gateway device or nearby for device jumping, you can install sensors with wireless transmitters on the basis of testing, and explore and quantify benefits Essence The prototype design can be designed for the improvement of data analysis, equipment monitoring and unit operation control, and records the cases of "previous" and "subsequent".

The integration installation of wireless transmitters provides flexibility and portability for the optimization of the online process and equipment performance indicators and the optimization of the measurement location.

Wearing transmitter
The header -mounted transmitter is a small disc various transmitter. They are usually installed in a protective shell -connecting header for direct installation or wiring box for remote installation.

Rail transmitter
The guide rail installation transmitter is designed to connect to the DIN guide rail (G guide rail or top hat guide) or screw directly to the wall. The guide rail installation transmitter is also designed to be installed compact, allowing multiple transmitters to be installed together very closely.

Direct wiring
As mentioned earlier, the direct wiring refers to the control system of the sensor's lead wiring. Because the lead (and original signal) of the sensor pass through the entire distance from the measurement point to the control system, we must pay attention to avoid two key issues:

● Noise -TC is particularly sensitive to noise interference. The extension line must be surrounded by source wiring such as generators and motors.
● Hot source -the huge changes in environmental temperature will affect the signal transmission of the sensor to the control system.
● Diversion resistance -the total resistance of the RTD temperature sensor lead and the resistance difference of the RTD temperature sensor leading resistance will affect the accuracy of the RTD temperature sensor. 3 wire transmitter input can compensate the total lead resistance. The 4 -wire transmitter input can compensate the difference in the lead resistance.
All temperature measurements that are important to analyze and control process analysis and control using on -site transmitters. If it is not restricted by accessibility or temperature, the transmitter should be installed on the thermocouple sleeve as a whole. It is best to use the tube joint to improve the disassembly of the sensor. Consider finding the possibility of the best measurement position, and explore the potential benefits of the additional temperature measurement and the prototype design to improve the process performance by using a portable wireless integrated installation transmitter.