A chemical plant is a fine chemical production unit. Its process control has high requirements for the accuracy of the temperature. Numerous temperature detection elements are involved in the safety chain process. At the same time, deviations in temperature accuracy directly affect the quality of the product, so temperature control plays a pivotal role in this industrial production.
1. Intelligent temperature transmitter selection reasons
1.1 Production environment
Many factors can cause electromagnetic interference in industrial production environments, such as communication equipment (mobile phones, walkie-talkies), motor rotation equipment, etc. Ordinary temperature sensors directly wired to the DCS control room, its RTD, thermocouple signal by the impact of nearby electromagnetic interference, easy to increase the resistance value, resulting in temperature detection value and the actual discrepancy, affecting the production process.
1.2 Control distance
For the temperature sensor far from the control room, long-distance transmission is not only easy to break the wire. But replacement is also time-consuming, laborious, and costly. The signal is easily attenuated, resulting in temperature control value instability, which sometimes seriously causes the production system to stop.
1.3 Production process
We use intelligent temperature transmitters to eliminate the above problems in the production process (based on microprocessor field installation of temperature transmitters). It solves the effects of electromagnetic interference. It also has the advantage of high performance and reasonable price, and its investment costs are almost equal to those of a direct wiring strategy. And the use of such intelligent instruments saves time. The features and advantages of this instrumentation are critical when the measurement points are transmitted over long distances to the control room.
2. A brief description of the smart temperature transmitter principle
There are two methods of bringing the measurement signal into the control room when carrying out temperature measurements. The first method is to use the output line of the sensor to transmit the signal (mV signal) generated by the RTD or thermocouple installed on site.
The other method is to install a temperature transmitter near the measurement point (the temperature transmitter is composed of a reference unit, an R/V conversion unit, linear circuit, reverse connection protection, current limiting protection, V/I conversion unit, etc. After the measurement resistance signal has been converted and amplified, the linear course repays the non-linear relationship between the temperature and the V/I conversion circuit. It outputs a 4-20mA signal with a linear relationship to the measured temperature). (constant current password), the transmitter will be the sensor signal amplified and transmitted to the control room through a twisted-pair cable.
3. Application
3.1 Reduced wiring costs
When we use ordinary temperature sensors, we can directly wire to the temperature sensor of the control system requires long-distance wiring. However, temperature transmitter wiring over long distances, the wire itself is straightforward to break, and the cost of ordinary transmission of temperature transmitter 4 ~ 20mA signal shielded copper wire more than three times.
When choosing an intelligent temperature transmitter, the signal can be sent directly to the control room using the wires from the original standard sensor. It saves installation time and the cost of installation materials (including the cost of conduit for placing the cables) in the replacement installation. Intelligent temperature transmitters reduce expenses while improving temperature measurement and control capabilities.
3.2 Protecting the signal from the effects of electromagnetic interference on site
Field temperature sensors use direct wiring to introduce signals into the control system. As a result, its RTD or thermocouple signals will be affected by electromagnetic interference generated by the surrounding equipment. And the sensor signal output wire will also become a conducive pathway for electromagnetic interference, thus affecting the transmitted signal so that the resistance increases, the temperature control measurement value is high, resulting in a false chain.
In contrast, the intelligent temperature transmitter will first convert the sensor signal into an analog signal (generally 4 to 20mA) and then transmit. Its constant current signal generated by the temperature transmitter amplification can effectively resist electromagnetic interference and can be transmitted over long distances in an environment with interference without affecting accuracy.
3.3 Blocking the ground loop
Field temperature sensors in the process of use due to working conditions, the surrounding environment, the impact of nearby sizeable rotating equipment, and other factors, often grounding phenomenon, resulting in high resistance, temperature measurement data abnormal.
The domestic intelligent temperature transmitter input/output is generally used photoelectric isolation and power supply signal using high-frequency transformer isolation to protect the call from the ground loop, effectively preventing the adverse effects of grounding.
3.4 Reducing hardware and storage costs
The type of temperature sensor and the DCS control system hardware must be matched. For example, a chemical plant uses RTD and thermocouple temperature sensors in-process production, which must be matched to the corresponding system cards, which requires the purchase of many different types of cards and the preparation of the related spare parts.
These cards are much more expensive per point than the 4-20mA input cards, increasing costs. The different types of cards can also cause a lot of inconvenience in installation, maintenance, and exchange.
The intelligent temperature transmitter contains a microprocessor that allows the output signal to be converted to a standard 4 to 20mA signal. As a result, it enables the selection of cheaper, universal analog input cards and reduces the amount of card storage in the system.
3.5 Enables perfect matching of different types of sensors and applications　
The use of intelligent temperature transmitters can make it easier to replace sensors. Replacing a temperature sensor that is not using a smart temperature transmitter involves changing the loop twisted pair and the 4 to 20mA input line and considering the change in temperature measurement values due to sensor interchangeability errors. The intelligent temperature transmitter only needs to be reconfigured for different sensor types to achieve a perfect match.
3.6 Enhanced accuracy and stability
It is well known that a more minor measuring range results in higher measuring accuracy. Therefore, intelligent temperature transmitters can be calibrated to fit into any interval within the full measurement capability of the sensor, making the measurement accuracy much higher than if the sensor was connected directly.
In addition, the intelligent temperature transmitter can be adapted to each sensor in use, resulting in a high degree of accuracy and minimal deviation from the required value, which also makes an excellent contribution to the stability of the temperature measurement and control value. It is undoubtedly a boon for industrial processes with high-temperature measurement and control values requirements.
3.7 Simplifies engineering and prevents miswiring
We use intelligent temperature transmitters, which replace various combinations of sensor wires and input boards for DCS control systems. It also simplifies engineering and drawing design (only the type (twisted pair) and one input board type (4 to 20mA) need to be specified at design time). In addition, this makes the instrument easy to maintain, and its current limiting and reverse connection protection circuitry significantly reduces and eliminates the possibility of circuit miswiring.
3.8 Simple upgrade operati
on (with HART communication protocol)
A chemical plant is transitioning to a fine chemical industry, where process optimization requires a change in the measurement range of specific temperature values or a higher level of measurement accuracy.
Thanks to the intelligent temperature transmitter with HART communication protocol, the output is no longer limited to a simple response to the measured temperature through the current value. At the same time, the HART modem communicates with the host PC or with the handheld and PC for remote information management, configuration, variable detection, and calibration of the transmitter model, index number, and range machine.
The modified parameters are transmitted down to the intelligent temperature transmitter, thus changing its performance to meet the needs of different field sensor types. Such smart temperature transmitters in the production meet the process requirements and make instrument maintenance easy and fast.
3.9 Reduced maintenance time and costs
The intelligent temperature transmitter’s self-diagnostic function allows accurate sensor operation tracking and rapid identification and diagnosis of sensor faults. It eliminates the need to remove the sensor or check all wires to locate the problem during maintenance. As a result, it reduces maintenance time and costs for dealing with temperature faults in actual production processes.
4. Conclusion
The use of intelligent temperature transmitters in the process of a chemical plant has solved the problem of poor temperature control accuracy and weak resistance to interference. It has dramatically improved the quality of process temperature control. Its selection is also an initiative to achieve industrial intelligence and save investment, providing a more reliable guarantee for the production line’s stable production and efficient operation. We can see that the application of intelligent temperature transmission has a broad space for development!