How to know the RTD temperature sensor and thermocouple temperature sensor?
To determine that a sensor may be a thermocouple or thermal resistance, the Vodio table is used to measure resistance. If the sensor has two wires, measure the resistance between the two wires. If the sensor is a thermocouple, you only need to measure the resistance of this wire.
The maximum temperature of most RTDS is limited to 1,000 Huali. In contrast, some thermocouples can be used to measure 2700 degrees Hua's.
The thermal release resistance temperature detector (RTDS) is specially designed to ensure accurate and repeated temperature and resistance characteristics. The sensor is built in a unique free strain free way and only uses high -quality RTD elements. According to the customer's requirements, ceramic, line wounds, flat film technology elements or special military anti -vibration elements to ensure the most suitable specifications. Features and benefits accuracy. A special process combined with the support of free building and the full entanglement support is reliable. The accurate reading is in the standard RTD component, and the platinum of the plane film component is etched on the substrate. High signal -to -noise ratio output. The accuracy of data transmission is added, and there is a greater distance between sensors and measuring devices. Interchangeability. No change structure and precision fine -tuning allowed elements to be replaced from different batches without re -calibration. Sensitivity. Self -heating is the smallest and allows accurate measurement. When the insulating resistance value exceeds the IEC-751 standard, the temperature coefficient (Alpha) strictly controls in accordance with industry standards. standardization. These elements can meet or exceed the requirements of various standardized agencies. IEC-751 standard tolerance level A and B are very suitable for industrial applications, respectively. As high as 1/10 din, the tolerance level can also provide higher accuracy requirements. Physics and chemical stability within a wider temperature range. Fireworks sales use a highly controlled production process. Standard elements are to establish resistance and impact resistance. However, in high mechanical vibration exposure, specially manufactured military specifications thick film RTD elements can provide suitable applications. Repeatability. Even at the temperature exposed to the operating range for a long time, the repetitive value of all components exceeds IEC-751.
Application
• Air adjustment and refrigeration service
•food processing
• Stove and grill
• Textile production
• Plastic processing
• Petrochemical processing
•Microelectronics
• Air, gas and liquid temperature measurement
• Exhaust gas temperature measurement.
When to use RTDS?
When accuracy and stability are the requirements of customer norms. The accuracy must be extended to a wide range of temperature.
• Regional induction rather than point sensing can improve control.
• When a high degree of standardization is required.
Advantage
• Linear phase for width work range
• Wide work temperature range
• High working temperature range
• Conversity is relative to wide working temperature range
• Good stability
Shortcoming
• Low sensitivity
• High cost
• No induction
• Affected by impact and vibration
• Require three or four -line operations
Install
When installing the RTD component, the main consideration is to have enough water to ensure that the RTD will not have the temperature of the equipment or structure outside the process and process of the RTD. RTD is not as measuring device like the thermocouple, so there is a active sensing area that needs to be completely immersed to ensure the actual process temperature of RTD measurement. When installing the thermal puppet, it is crucial to be a good thermal conductivity of 40mm along the sensor shaft. Active sensing area of RTD sensor. This area will vary according to the length of the RTD component used in the building. You can design the sensor to display the average temperature.
Select the right temperature sensor When choosing an RTD element that suits your needs, there are many choices to consider:
Temperature rated value tolerance, accuracy and interchangeability time response distance control or measurement equipment. The most commonly used structure is to put RTD components and connected wires in a closed metal tube, use vibration damping and/or heat transmission materials such as aluminum oxide wrap pipes, and use epoxy resin, silicon resin or ceramic cement seal tube Open. The most commonly used metal tube in RTD is made of 316 stainless steel (for about 480 ° C). The vibration damping/heat transfer material used changes greatly within the temperature range. These materials are chosen by the manufacturer, which is expected to be used on the basis of providing the best performance.
Another common structure is to use mineral insulation metal sheath (MIMS) cables, where RTD components insert a drilling hole and connect to nickel or copper wires that are insulated from magnesium oxide (MGO). The end is then welded with MGO insulation and end welding, and the other end is sealed before the extension line connection. Epoxy sealing compounds usually do not use more than 200 to 260 ° C. Ceramic cement can be exposed at a temperature of 1200 ° C or higher, but it is necessary to seal glue to prevent the water at the bottom of the water and the heat transfer material at the bottom of the cement. Materials with minimum temperature performance in Platinum RTD are usually wires and insulation used in its structure. There are two structures, low temperature and high temperature. In the low temperature structure, Telmon -insulating nickel -plated copper wire is used to connect to RTD components. Fill the alumina powder in stainless steel pipes to support the element and have epoxy sealing. This structure is usually limited to 250 ° C. The high -temperature structure uses nickel lines and ceramic insulators, or MIMS cables containing nickel wires. Nickel wire and ceramic structure are supported components to fill alumina powder. The sealing glue used depends on the temperature level of the transition point. These two types of structures can be used for about 650 ° C, but by carefully selecting components and using the cover of the cover of the cover, it can be extended to about 850 ° C.
Tolerance, accuracy and interchangeability Tolerance and accuracy are the most misunderstood terms in temperature measurement. The term tolerance refers to the degree of uncertainty or possible errors on a specific point. Accuracy refers to unlimited tolerances within the specified range. For example, RTD contains a sensor element with a specific resistance at a specific temperature. The most common example of this requirement is the so -called DIN/IEC standard. In order to meet the requirements of the DIN/IEC standard, the resistance of RTD at 0 ° C must be 100 ohm ± 0.12%(or 0.12 ohm) in order to be considered a B -class sensor (A -class sensor is 100 ohm ± 0.06%). ± 0.12 ohm tolerance is only applicable to the resistance of 0 ° C and cannot be applicable to any other temperature. Below is the exchange table of Class A RTD, which provides users with a tolerance table at a specific temperature. The lead resistance has a great impact on the measurement resistance. This compensation ability
Additional resistance will affect the selected component type and system accuracy. The most common assembly type is the 3 的 line RTD. Here, the lead resistance is compensated in the bridge circuit. In order to achieve the highest accuracy, the only choice is to use the 4 -line RTD to eliminate the binding resistance error.
Response time
When selecting the preparation method that suits you best, the response speed of the sensor to temperature changes must be considered. If you use the thermocouple, the response time will be significantly increased, and you must be careful when designing the thermocouple/sensor system. The inner diameter of the thermocouple sleeve should be closely matched with the diameter of the RTD to achieve good thermal contact, thereby maximizing the heat transfer.
If the fast time response is a standard, the smaller the element and probe, the faster the time response. Between the implementable response time and the adaptability of the sensor to adapt to the process environment.
Where to install the distance RTD component between the control or measuring device, the RTD type required for the specified. If the control/measurement point is relatively close to the installation sensor, you can directly connect to the instrument with a cable. For a longer distance, check the input specifications of the instrument to determine whether the lead impedance is too large. In this case, it is recommended to use a 4 - 20mA transmitter. (4 - 20mA transmitter converts the resistance to current and transmits it through the 2‐ line at the minimum loss).
Troubleshooting
Problems related to RTD components are often simple and easy to solve. Because RTD components are easily damaged by vibration or mechanical impact, the most likely problem is that the component is open. According to the type of component, this can be easily determined with a multimeter. The drift problem is often more delicate. Because platinum is easily contaminated, the introduction of impurities can change the base resistance. The resistance to the temperature response can
This is very different from pure platinum. In this case, the only way to determine whether there is an error is to calibrate the RTD sensor.
Each temperature sensor has its unique advantages and disadvantages.
RTD temperature sensor advantages
Each temperature sensor has its unique advantages and disadvantages.
Advantages of RTD:
PT100 temperature sensor RTD is usually used for applications with very important applications for repetitiveness and accuracy
consider. The correct constructed PT100 RTD has the repetitive resistance temperature characteristics that changes over time. If a process will run at a specific temperature, the RTD resistance at the temperature can be determined in the laboratory, and it will not change significantly over time. RTD also allows easier interchangeability because their initial changes are much lower than that of thermocouple. For example, the standard error limit of the K -type thermocouple used in 200 ° C is ± 2.2 ° C. A pt100ohm din, B -Class Platinum RTD has the interchangeability of ± 1.3 ° C at the same temperature. RTD can also be displayed or displayed with the standard instrument cable or
In the control device, the thermocouple must have the corresponding thermoelectric puppet to obtain accurate measurement.
The disadvantages of RTD Under the same configuration, you can expect more money for RTD than cheap metal thermocouples. RTD is more expensive than thermocouple, because manufacturing RTD requires more structures, including the manufacturing of sensor elements, the connection of the extension line, and the assembly of the sensor. Due to the structure of the sensing element, the performance of RTD in high vibration and mechanical impact environment is not as good as armocouple. The temperature of the industrial RTD is also limited to 650 ° C, while the thermocouple can use up to 1700 ° C.
Life life
The life of thermocouple use. Useful thermocouple life is a very difficult forecast, even if most details of the application environment are known. Unfortunately, such information is often difficult to determine. For any application environment, the best test is the use performance of installation, use and evaluation that is considered to be successful. The suggestions and non -suggestions listed in the thermocouple type description are a good place to start when the assembly style that is installed in the process for the first time.
Offset and drift
Stability all thermocouples will be affected by calibration drift during use. This is only how much problem, and how fast this situation occurs. The performance of the thermocouple is seriously dependent on the absolute uniformity of physical and chemical properties in the length of the entire circuit. When producing thermocouple material, take careful steps to ensure that this uniformity (or uniformity) should be achieved. During the use process, different parts of the circuit will go through different thermal and chemical exposure conditions, so the physical structure and composition of these parts will change from the original thermal power line. Because the thermomotive force generated by the given temperature difference is very sensitive to the changes in the chemical and metallurgical properties of the wire, under the same conditions, the total electromotive force generated by the use probe may be different from other new probes. These changes are usually small within observed time (usually small enough to be ignored). However, under unfavorable conditions, it is possible to achieve rapid drift speed. In order to achieve long -term reliable thermocouple life, the usual strategy is to comfortably operate the equipment at the highest temperature and provide it as a clean working environment as possible. Shells, such as sheets, protective tubes, and thermometer sleeves, are common methods to control the surrounding environment of the thermocouple itself.
Common faults
Protective tube, protective cover, and even thermometer sleeve may fail due to corrosion or mechanical damage. The process can be more temperature and expose the heat components at a higher temperature than expected. If the sensor of the control process is low in its output, the process of responding to its controller may be forced to accept temperatures higher than expected temperature. The cheap metal components are easily eroded by a variety of chemical agents. They also change due to unfavorable operating conditions. According to the supply, high -quality precious metal thermal puppets are very low in impurities. Therefore, it is vulnerable to pollution, which affects its thermal power performance. Platinum is particularly sensitive to the existence of free silicon. It can form a common crystal alloy with free silicon to melt when normal use temperature or lower than normal use temperature. The high -purity insulation and protective tube of valuable metal components, as well as paying attention to cleaning during processing, will help prevent this. Human errors may also be a factor. The control may be incorrect, the connection may be incorrect, and the response operation conditions may be inappropriate.
Failure exclusion To evaluate the question, please check whether the system performance is reasonable
Is the change in the control produced the logical result? How about the product? Is its condition complied with the instrument display?
How to test the use of thermocyst First of all, it is not always feasible to remove suspicious thermocets from the service and "test" in another place. Once the device is used, it means that it may no longer be homogeneous. Different temperature gradients are applied to the uneven thermal power puppet, even if there are only slight differences, it will cause different output and readings. Re -calibrating a used thermocouple will definitely produce a "number", but this number may be meaningless in the use of the thermocouple. The best way to evaluate the use of thermocouples is the "detection" position. Place a new thermocouple with known output output next to the suspicious thermocouple in the operation, and compare the readings. It is unrealistic if there are two sensors at the same time. Remove the suspicious probe and replace it with another well -known good probe. Then, as long as the good probe is located in the same position as the removed probe, and the process has not changed during the exchange process, you can compare the readings of the two probes. Please note that there is no need to retain and use unlimited new probes for these tests. You can retain some appropriate alternative equipment and choose one for testing. Under
Under normal circumstances, thermocouple drift or degeneration is a gradual and very slow process. Therefore, a single alternative probe can be used to detect a process multiple times and is considered a reliable repeated test. Moreover, when a drifting probe is found, the test probe can be simply stayed as a working sensor, and the next alternative becomes a test device.
System Test
Portable temperature index is a useful instrument to diagnose the failure of the thermocouple system. Many of these devices can work with two or more different thermocouple types. Some devices provide a "output" function, which will produce an electronic output to simulate the thermocouples at any temperature. In use, the instrument is usually connected to the wires of the tested circuit, at some convenient access points, such as connectors. Pay attention to ensure that the correct polarity is maintained. We use ANSI color code where we are where the negatives are
Always red. There, you can monitor and evaluate the output of running sensors. Alternatively, using the "output" function of the instrument can send the simulated thermocouple signal back to the permanent indicator or controller of the circuit to verify the normal operation of the remaining circuits.
When a signal is driven to return to the instrument, the side of the disconnection of the circuit is usually required to avoid the portable tester "load" due to the low resistance of the thermocouple itself. The thermocouple circuit The part of the extended line can also be checked whether it is correctly connected with a portable tester. The tested part should be isolated from the rest of the circuit. One end of the extended line should be connected short. If the tester is connected to the other end of the short pair, the tester should display the short -paired near temperature. Note that if the two ends of the pair are just at the same temperature, it may be necessary to heat the short -end and verify that the tester "see" the temperature change correctly. In this test, the possibility of incorrect and reverse connection is being inspected.
Thermal resistance or thermocouple: Thermocouple and thermocouple are useful temperature sensors to determine the temperature of the process. In its temperature range, the RTD temperature sensor has higher accuracy than the thermocouple temperature sensor , because platinum is a more stable material than most thermocouple materials. RTD also uses a standard instrument line to connect to measurement or control device, which can reduce the overall installation cost. Thermocouple is generally cheaper than RTD. They are more long -lasting high vibration or mechanical impact applications, which can be used for higher temperatures. The size of the thermocouple can be smaller than most RTD temperature sensors, and they can be formed based on specific applications.
