First, the problem phenomenon: transmitter no outputFinding the cause1, check whether the power supply of the transmitter is reversed;2、Measure the power supply of the transmitter, whether there is 24V DC voltage;3, if it is with a meter head, check whether the meter head is damaged (you can first short-circuit the two wires of the meter head, if it is normal after short-circuiting, it means that the meter head is damaged);4, the ammeter will be strung into the 24V power supply circuit, check whether the current is normal;5, whether the power supply is connected to the transmitter power input;method settle an issue1. Connect the power supply polarity correctly.2, must ensure that the power supply voltage supplied to the transmitter ≥ 12V (i.e. transmitter power input voltage ≥ 12V).3、If there is no power supply, you should check whether the circuit is disconnected and whether the detection meter is selected incorrectly (input impedance should be ≤250Ω);4, if the meter head is damaged, it is necessary to change another meter head, if it is normal, it means that the transmitter is normal, at this time, we should check whether the other instruments in the circuit are normal.5、Connect the power cord to the power terminal.Second, the problem phenomenon: transmitter output ≥ 20mAFinding the cause1, whether the transmitter power supply is normal2, whether the actual pressure exceeds the selected range of the pressure transmitter;3, whether the pressure sensor is damaged, serious overload will sometimes damage the isolation diaphragm.4, whether the wiring is loose;5, whether the power line wiring is correctmethod settle an issue1, if the transmitter power supply is less than 12VDC, should check whether there is a large load in the circuit, the input impedance of the transmitter load should be in line with the RL ≤ (transmitter power supply voltage - 12V) / ( 0.02A) Ω2、Re-select the appropriate range of the pressure transmitter.3、Pressure sensor, if damaged, need to be sent back to the manufacturer for repair.4、Connect the line and tighten it.5, the power cord should be connected to the appropriate terminal.Third, the problem phenomenon: transmitter output ≤ 4mAFinding the cause1, whether the transmitter power supply is normal2, whether the actual pressure exceeds the selected range of the pressure transmitter;3, whether the pressure sensor is damaged, serious overload will sometimes damage the isolation diaphragm.method settle an issue1, transmitter power supply if less than 12VDC, should check whether there is a large load in the circuit, transmitter load input impedance should be consistent with the RL ≤ (transmitter power supply voltage - 12V)/( 0.02A) Ω .2、Re-select the appropriate range of the pressure transmitter.3、Pressure sensor, if damaged, need to be sent back to the manufacturer for repair.IV. Problem phenomenon: incorrect pressure indicationFinding the cause1、Whether the power supply of the transmitter is normal2, reference to the pressure value must be correct3、Is the range of the pressure indicator consistent with the range of the pressure transmitter?4、Is the input of the pressure indicator and the corresponding wiring correct?5, the input impedance of the transmitter load should be consistent with RL ≤ (transmitter supply voltage - 12V) / ( 0.02A) Ω6、Multi-point paper recorder is not recorded when the input is open circuit;7, whether the corresponding equipment shell grounding8, whether the AC power supply and other power supply separate lines9, whether the pressure sensor is damaged, serious overload will sometimes damage the isolation diaphragm.10, whether there is sand in the pipeline, impurities and other blockage of the pipeline, impurities will make the measurement accuracy is affected;11, whether the temperature of the pipeline is too high, the use of the pressure sensor temperature is -25 ~ 85 ℃, but the actual use of -20 ~ 70 ℃ or less.method settle an issue1、Transmitter power supply if less than 12VDC, should check whether there is a large load in the circuit, the input impedance of the transmitter load should be consistent with the RL ≤ (transmitter power supply voltage - 12V)/( 0.02A) Ω.2、If the accuracy of the reference pressure gauge is low, it is necessary to change another pressure gauge with higher accuracy.3. The range of the pressure indicating instrument must be the same as the range of the pressure transmitter.4, the input of the pressure indicating instrument is 4 ~ 20mA, the transmitter output signal can be directly accessed; if the input of the pressure indicating instrument is 1 ~ 5V, the pressure indicating instrument must be connected to the input of the precision of the instrument in one thousandth and above, the resistance value of 250Ω resistor, and then access to the input of the transmitter.5, the input impedance of the transmitter load should be in line with RL ≤, if not in line with the different measures that can be taken according to its different: such as increasing the supply voltage (but must be lower than 36VDC), reduce the load.6、Multi-point paper recorder is not recorded when the input is open-circuit, then: 1, can not take other loads; 2, change to other no record when the input impedance ≤ 250Ω recorder.7, the corresponding equipment shell grounding.8, and AC power supply and other power supply separate wiring.9, the pressure sensor is damaged, need to be sent back to the manufacturer for repair.10, the pipeline sand, impurities and other blockage of the pipeline, you need to clean up impurities, and in front of the pressure interface with a filter.11, the pipeline temperature is too high, plus buffer tube to dissipate heat, add some cold water in the buffer tube before use, in order to prevent overheating of steam directly impact the sensor, thereby damaging the sensor or reducing the service life!

Radar level meters are widely used in industry as a common level measurement device. However, in some specific cases, radar level meters require additional heat sinks for heat dissipation. This article will introduce when a radar level meter needs an additional heat sink and provide an actual measurement case to illustrate the application of the heat sink.Application of Radar Level Meter Heat Sinks, Normally, radar level meters are able to perform level measurement well under normal operating conditions. However, in the following cases, due to the special requirements of the environment or measurement conditions, such as high-temperature environment or long-term stable measurement needs, it may be necessary to add a heat sink: High-temperature environment: In a high-temperature environment, the radar level meter may be affected by the temperature and lead to an increase in the measurement error. In this case, by installing a heat sink, the radar level meter can be separated from the temperature of the surrounding environment, effectively reducing the impact of temperature on the measurement. Long-term stable measurement: In scenarios where long-term stable level measurement is required, the radar level meter may be subjected to a certain amount of heat due to prolonged operation. Excessive temperature may lead to inaccuracy of measurement or even damage the device. By adding a heat sink, the heat dissipation technology can be effectively used to reduce the heat of the device and ensure long-term stable measurement results. High-viscosity liquids: When measuring high-viscosity liquids, the radar level meter may be affected by the liquid adhering to the sensor, leading to measurement deviation. By using a heat sink to reduce the temperature of the sensor surface, the adhesion phenomenon can be reduced and the accuracy of the measurement can be improved.In order to better understand the application of radar level meter heat sink, let's look at an actual measurement case. A chemical factory uses radar level meter to measure the level of a high-temperature liquid. Under the condition of high ambient temperature, the radar level meter found that the measurement result had some deviation after working continuously for a period of time. After analyzing the situation, the engineers determined that they needed to add a heat sink to solve the problem. After the modification of the radar level meter, the engineers installed the heat sink on the back of the device. The heat sink conducts the heat generated by the device to the external environment through thermal conductivity technology, which maintains the appropriate working temperature of the device. After a period of operation, the engineers found that the measurement results became more stable and accurate. By adding the heat sink, the radar level meter maintains a stable working condition in a high temperature environment, thus ensuring the accuracy of level measurement. In addition, the use of heat sinks also extends the service life of the equipment and improves its reliability.Radar level meters can perform level measurement normally under general process conditions. However, in some specific environments and measurement needs, such as high-temperature environments, long-term stable measurement and other conditions need to add a heat sink, the actual application needs to be based on specific circumstances.

Temperature is defined as the energy level of a substance and can be demonstrated by certain changes in that substance. There are many types of temperature measurement sensors and they all have one thing in common: they all measure temperature by sensing some change in physical properties. The seven basic types of temperature sensor transmitter discussed here are thermocouples, resistance temperature devices (RTDs, thermistors), infrared emitters, bimetallic devices, liquid expansion devices, molecular state changes, and silicon diodes. Whether it is a thermometer or a thermocouple, different types of sensors can measure temperature.1. Thermocouples Thermocouples are voltage devices that indicate temperature measurements as the voltage changes. As the temperature increases, the output voltage of the thermocouple rises - not necessarily linearly. Thermocouples are usually located inside a metal or ceramic shield to protect them from exposure to various environments. Metal jacketed thermocouples are also available with many types of external coatings, such as Teflon, for trouble-free use in acids and strong alkaline solutions. 2. Resistance Temperature Measuring Devices Resistance temperature measuring devices are also electrical in nature. Instead of using voltage like thermocouples, it utilizes resistance, another property of matter that varies with temperature. And the resistive devices used can be categorized into: metal resistance temperature devices (RTD) and thermistors. In general, RTDs are more linear than thermocouples. They increase in a positive direction, with resistance rising as the temperature increases. A thermistor, on the other hand, has a completely different type of construction. It is an extremely non-linear, semi-conducting device that decreases in resistance as the temperature increases.3. Infrared sensors Infrared sensors are non-contact sensors. For example, if you hold a typical infrared sensor up to the front of a table without contact, the infrared liquid level sensor will tell you the temperature of the table by its radiation - about 68°F at normal room temperature. In non-contact ice water measurements, due to evaporation, the ice water measures slightly at 0°C, which slightly reduces the expected temperature reading . 4. Bimetallic Devices Bimetallic devices take advantage of the expansion of metals during heating. In these devices, two metals are combined and mechanically connected to a pointer. When heated, one side of the bimetallic strip will expand more than the other. And when properly aligned with the pointer, it will display the temperature measurement. The advantages of bimetallic devices are portability and independence from the power source. However, they are usually not as accurate as electrical devices, and you can't easily record temperature values with electrical devices like thermocouples or RTDs. But portability is a definite advantage for the right application. 5. Thermometers Thermometers are familiar liquid expansion devices that are also used for temperature measurement. In general, they fall into two main categories: the mercury type and the organic (usually red) liquid type. The difference between the two is clear, as mercury devices have some limitations on how they can be safely transported or shipped. For example, mercury is considered an environmental contaminant, so breakage can be dangerous. Be sure to check current restrictions on air transportation of mercury products before shipping.6. Change of state sensors A change of state temperature sensor measures the change in state of a material brought about by a change in temperature, like the change from ice to water to steam. Commercially available devices of this type are in the form of labels, pellets, crayons, or paint. For example, labels can be used on steam traps. When the trap needs to be adjusted, it gets hot; the white dot on the label then indicates the rise in temperature by turning black. The white dot remains black even when the temperature returns to normal. The Change of Condition label indicates the temperature measurement in °F and °C. For these types of devices, the white dot turns black when the displayed temperature is exceeded; and it is an irreversible sensor that stays black once it changes color. Temperature labels are useful when you need to confirm that the temperature has not exceeded a certain level, perhaps during transportation for engineering or legal reasons. Since change of state devices are non-electrical like bimetallic strips, they are advantageous in some applications. Some forms of this family of level sensors (lacquer, crayon) do not change color; the markings they make simply disappear. Granular forms, on the other hand, will visually distort or melt away completely. Limitations include relatively slow response times. So if you have a spike in temperature that goes up and then quickly goes down, there may not be a noticeable response. Accuracy is also not as high as most other devices commonly used in industry. However, they are very practical in applications where you need non-reversible indications that do not require a power source. Other reversible labels operate on a completely different principle than using an LCD display. Depending on the temperature reached, the display changes color from black to brown, blue or green. For example, a typical label is all black at temperatures below that sensed. As the temperature measurement rises, a color appears at, say, 33°F-first blue, then green, and finally brown-as it passes through the specified temperature. In any given LCD device, you will usually see two adjacent color dots - the blue one slightly below the temperature indicator and the brown one slightly above it. This allows you to estimate the temperature, for example, between 85° and 90°F. Although it is not entirely accurate, it has the advantage of being a small, rugged, non-electronic indicator that continuously updates the temperature measurement. 7. Silicon Diode Silicon diode sensors are devices developed specifically for the low temperature range. Essentially, they are linear devices where the conductivity of the diode increases linearly in the low temperature region. No matter what sensor you choose, it will not work alone. Since most sensor choices overlap in temperature range and accuracy, the choice of sensor will depend on how it is integrated into a system.

                                                                                                                       Why should transmitters and sensors use 4～20mA as transmission signal?I. What is 4～20mA.DC (1～5V.DC) signaling system?4～20mA.DC (1～5V.DC) signal system is the International Electrotechnical Commission (IEC): analog signal standard for process control system. Our country from DDZ-Ⅲ type electric instrumentation began to use this international standard signaling system, instrument transmission signal using 4 ~ 20mA.DC, contact signal using 1 ~ 5V.DC, that is, the use of current transmission, voltage receiving signal system.4~20mA current loop working principle:In the industrial field, using an instrumentation amplifier to complete the signal conditioning and transmit it over a long line will cause the following problems: firstly, since the transmitted signal is a voltage signal, the transmission line will be interfered with by noise; secondly, the distribution resistance of the transmission line will generate voltage drop; thirdly, how to provide the working voltage of the instrumentation amplifier in the field is also a problem.In order to solve the above problems and avoid the influence of related noise, we use current to transmit the signal, because the current is not sensitive to the noise. 4～20mA current loop is to use 4mA to indicate the zero signal, and use 20mA to indicate the full scale of the signal, and the signal lower than 4mA and higher than 20mA is used for various kinds of fault alarms.                                                                                                                                                                                          (Image source: Internet)Second, 4 ~ 20mA.DC (1 ~ 5V.DC) signal system advantages?Field instrumentation can be realized two-wire system, the so-called two-wire system that the power supply, load in series, there is a common point, and the field transmitter and control room instrumentation before the signal contact and power supply with only two wires. Because the signal starting current of temperature sensor 4-20ma.DC, for the transmitter to provide a static operating current, while the instrument electrical zero point of 4mA.DC, not coincide with the mechanical zero point, this "live zero" is conducive to the identification of power outages and disconnections and other faults. And two-wire system is also convenient to use the safety grid, conducive to safety and explosion-proof. 　　Control room instrumentation using voltage parallel signal transmission, the same control system belongs to the instrumentation between the public terminal, easy to detect the instrument, regulating instrumentation, computers, alarm devices with, and convenient wiring. 　　The reason for using 4~20mA.DC as the contact signal between the field instrument and the control room instrument is that: because the distance between the field and the control room is far, the resistance of the connecting wires is large, if the voltage signal is used for remote transmission, it is better than the resistance of the wires and the voltage division of the input resistance of the receiving instrument, which will produce a large error, while using the signal of the constant current source as the remote transmission, as long as the transmission loop does not branch, the current in the loop will not change with the length of the wires, and the current in the loop will not change with the length of the wires. change with the length of the wire, thus ensuring the accuracy of the transmission. 　　The reason for using 1~5V.DC as the contact signal between the instruments in the control room is: in order to facilitate the common reception of the same signal by multiple instruments and to facilitate the wiring and the formation of various complex control systems. If the current source as a contact signal, when more than one instrument to receive the same signal, their input resistance must be connected in series, which will make the maximum load resistance exceeds the load capacity of the transmitter instrument, and the negative end of the signal of the receiving instrument potential is different, it will introduce interference, and can not be done in a single centralized power supply. 　　The use of voltage source signal contact, contact with the field instrumentation with the current signal must be converted to a voltage signal, the simplest way is: in the current transmission loop in series with a 250Ω standard resistor, the temperature sensor 4-20ma.DC converted to 1 ~ 5V.DC, usually by the distributor to complete this task.Third, why transmitters choose 4 ~ 20mA.DC for transmission signal?1, first from the field application of safety considerations 　　Safety focus on explosion-proof safety spark-type instrument to consider, and to control the instrument energy as a prerequisite to maintain the normal operation of the instrument static and dynamic power consumption is reduced to a minimum. Output 4 ~ 20mA.DC standard signal transmitter, its power supply voltage is usually 24V.DC, the main reason for the use of DC voltage is that you can not use large-capacity capacitors and inductors, it is only necessary to consider the transmitter and the control room instrumentation connected to the distribution of capacitance and inductance of the wire, such as 2mm 2 of the wire and its capacitance distribution of 0.05μ/km or so; for a single wire inductance of 0.4mH/km or so; much lower than the detonation of hydrogen. km or so; much lower than the value of the detonation of hydrogen, which is obviously very favorable to explosion-proof. 　　2, the transmission of signals with a current source is better than the voltage source 　　Because of the distance between the scene and the control room, connecting the wire resistance is large, if the voltage source signal transmission, due to the wire resistance and receiving instrument input resistance of the voltage division, will produce a large error, if the current source signal as a remote transmission, as long as the transmission loop does not appear branch, the current in the loop will not change with the length of the wire, thus ensuring the accuracy of the transmission. 　　3, the maximum signal current selection of 20mA reasons 　　The choice of maximum current 20mA is based on safety, practicality, power consumption, cost considerations. Safe spark instrumentation can only be used for low voltage, low current, 4 ~ 20mA current and 24V.DC is also safe for flammable hydrogen, for 24V.DC hydrogen detonation current of 200mA, far more than 20mA, in addition to comprehensively consider the connection distance between the production site instrumentation, with the load and other factors; and power consumption and cost issues, the requirements of the electronic components, power supply power requirements and other factors. Requirements for electronic components, power supply and other factors. 　　4, the starting current of the signal to choose the reason for 4mA 　　Output of 4 ~ 20mA transmitter to the majority of two-wire system, two-wire system, that is, the power supply, the load is connected in series, there is a common point, and the field transmitter and the control room instrumentation between the signal contact and power supply with only two wires. Why is the starting point signal is not 0mA, which is based on two points: First, the transmitter circuit will not work without static current, the signal starting point current 4mA.DC, not coincide with the mechanical zero, this "live zero" is conducive to the identification of power outages and disconnections and other faults.Four, the origin of 4 ~ 20mA sensor?The reason for using the current signal is not easy to be disturbed, and the current source of internal resistance is infinite, wire resistance in series in the loop does not affect the accuracy, in the ordinary twisted-pair cable can be transmitted hundreds of meters. 　　The reason for using the current signal is not easy to be disturbed, because the amplitude of the noise voltage in the industrial field may reach several V, but the power of the noise is very weak, so the noise current is usually less than nA level, so the error brought to the 4-20mA transmission is very small; the internal resistance of the current source tends to be infinite, and the lead wire resistor is connected in series in the loop without affecting the accuracy, so it can be transmitted hundreds of meters on the common twisted-pair cable; due to the large internal resistance of the current source and the constant resistance, the lead wire resistance is connected in series in the loop without affecting the accuracy, so it can be transmitted hundreds of meters on the common twisted-pair cable. Due to the large internal resistance of the current source and the constant current output, we only need to place a 250 ohm resistor to ground on the receiving end to obtain 0-5V voltage, the advantage of low input impedance receiver is that the nA level of input current noise produces only a very weak voltage noise. 　　The upper limit of 20mA is taken because of explosion-proof requirements: the spark energy caused by the interruption of a 20mA current is not sufficient to ignite the gas. The reason why the lower limit is not taken as 0mA is in order to be able to detect line breaks: in normal operation it will not be lower than 4mA, and when the transmission line is broken due to a fault, the loop current drops to 0. 2mA is often taken as the alarm value for a broken line. Current transmitter will be converted into physical quantities of 4 ~ 20mA current output, there must be an external power supply for its power supply. The most typical is the transmitter needs two power lines, plus two current output line, a total of 4 wires to be connected, called four-wire transmitter. Of course, the current output can be common with the power supply a common line common VCC or GND, can save a line, called three-wire transmitter. In fact, you may notice that the 4-20mA current itself can power the transmitter. The transmitter in the circuit is equivalent to a special load, the special thing is that the transmitter's power consumption current between 4-20mA according to the 4 20ma temperature sensor output and change. The display meter is simply strung in the circuit. This type of transmitter requires only two external wires and is therefore called a two-wire transmitter. The lower limit of the industrial current loop standard is 4mA, so the transmitter is supplied with at least 4mA as long as it is within the range. 　　Therefore, the 4-20mA signal output is generally not easily disturbed and safe and reliable, so the industry is commonly used in the two-wire 4-20mA power output signal. But in order to better deal with the 4 20ma temperature sensor's signal, there are more other forms of output signals: 3.33MV/V; 2MV/V; 0-5V; 0-10V and so on.