Temperature is a commonly used measurement parameter. Temperature sensors are used in instruments that measure temperature. To ensure precision and accuracy, all temperature sensors must be calibrated according to known specifications. However, there will be a variety of problems in the daily calibration process, and the following Hequan editor has sorted out the eight reasons why the temperature sensor cannot be calibrated, which is as follows:
Temperature sensor
1. Self-heating in thermistors and PRTs
When calibrating the thermistor and PRT, a nominal excitation current is applied. The amount of current required is generally stated in the calibration report or the manufacturer's specifications.
We know from Ohm's law that when an electric current flows through a resistor, it consumes power (I2R). This power causes the sensor to heat up; This is known as "self-heating". After calibrating the temperature sensor, its self-heating has been taken into account.
When using any type of sensor, make sure that the readings are set to the appropriate excitation current. Too little or too much current can lead to measurement errors. If too much current is applied, these sensors may even be damaged.
When "Thermistor" or "PRT" is selected, some readings actively select the appropriate current. Others may need to be set up manually. These settings are typically found in the probe settings menu. If you select the current manually, always refer to the thermometer's specifications or calibration report for the correct current.
2. Low insulation resistance and leakage current
Low insulation resistance is sometimes referred to as shunt resistance due to the fact that the current is allowed to flow outside the measurement circuit. Electrically, it's like connecting another resistor in parallel with a sensor. When low insulation resistance is generated, the transition junction temperature often becomes too hot. (The hub shouldn't be so hot that it's hard to touch.) )
In addition, if the sheath is bent or the seal is damaged, it may result in low insulation resistance, which can then allow moisture to enter the sensor and wires. This problem can generally be avoided with proper application and treatment.
3. Transition connection point
Thermistors and PRTs generally have transition junctions. The transition point is the orientation of the cable wire to the sensor wire. The leads will be soldered or spot welded. If they are soldered and the junction becomes too hot, the solder will melt and then cause an open circuit or intermittent condition.
Generally, the knot is sealed with epoxy resin to avoid moisture and other contaminants. If the seal accepts a temperature that exceeds the temperature that the epoxy cannot accept, the seal may break. This allows moisture and other contaminants to penetrate the seal and reach the wires and sensors. Moisture accumulates when the temperature sensor is immersed at a temperature lower than ambient or when the ambient humidity is high.
PRT is generally packaged with powdered insulation. This material makes PRT less simple to be affected by stresses caused by mechanical shocks. Unless outstanding sealing is present, the insulation absorbs moisture from the air at low temperatures. Moisture or other contaminants can cause measurement errors and cause temperature sensors to fail to calibrate. Trapped moisture can also pose a safety hazard. If the insulation absorbs a lot of moisture and the temperature sensor is exposed to a high temperature heat source, the moisture will turn into vapor, which may cause the seal to blow up or crack the sheath.
4. The wire is cracked or intermittent
If pulled, overworked, or subjected to pressure, the cable may crack, which can lead to breakage or disconnection. Occasionally, the sensor or sensor leads may be disconnected or intermittent. It wasn't until the temperature sensor was heated, causing the wires to swell and separate, that some intermittent events went unnoticed.
Even though great care has been taken to avoid disconnected or intermittent connections, they may still arise if there are enough moments and moments of use. Repeated expansion and contraction of wires and sensor wires may eventually lead to casualties, which can then lead to wire cracking.
5. Pollution
Contamination may be caused by chemicals, metal ions, or oxidation.
If liquid reaches the lead or sensor lead, chemical contamination may occur in the PRT. This alters the purity of the platinum and then its electrical properties. Any change in purity is sexual.
Metal ion contamination of platinum wires typically occurs at temperatures of 600oC or higher. Because PRT sensors are made with high-purity platinum wire, they are the least susceptible to this type of contamination. The contamination of metal ions is irreversible and will cause the temperature of PRT to rise. This is particularly significant in three-water level batteries with extremely stable reference temperatures. When PRT is made for extremely high temperatures, it should be constructed so that the sensor is free from ionic contamination.
Temperature sensor housings are generally sealed to avoid contamination. Neither the industrial temperature sensor nor the auxiliary temperature sensor is emptied before sealing. So, in general, there will be some dry air inside them. When exposed to a wide range of temperatures, they can form oxidation on the surface of the wire. Oxidation primarily affects temperature sensors, whose sensing elements contain platinum wires. Oxidation causes an increase in RTPW (resistance at the three-phase point of water) in metal RTDs. Fortunately, it was possible to remove oxidation by annealing the RTD using the temperature and process recommended by the manufacturer. Before and after annealing, the temperature sensor is compared with specifications such as the three-point accuracy of the water tank. This enables you to confirm that the process was successful,
6. Hysteresis and non-repetition
Hysteresis is a condition in which the readings of the temperature sensor lag or have a "memory" effect when the thermometer moves within a successive temperature scale. The measurement depends on the previous temperature at which the sensor or wire was exposed. If a temperature sensor passes through a certain scale of temperature (e.g., from cold to hot), it will follow a specific curve. If the measurements are repeated in reverse order (cold to hot in our example), the thermometer with the hysteresis problem will deviate from the previous set of measurements. If it is repeated, the offset may not always be the same.
The intact specification platinum resistance thermometer (SPRT) does not exhibit hysteresis due to the SPRT being planned to be strain-free. However, rugged PRT is not strain-free and has at least some lag. Moisture ingress or moisture entering the inside of a temperature sensor can cause hysteresis in any type of RTD.
7. Inhomogeneity
When thermocouples are used at high temperatures, their wires may become contaminated. This results in a partial change in the Seebeck coefficient of the wire from its initial condition. In other words, this modifies the wire's sensitivity to temperature changes. However, the exposed temperature and contamination along the length of the thermocouple may not be uniform. The Seebeck coefficient then becomes a function of the orientation along the thermocouple. This results in a measurement error that depends on the temperature profile accepted by the thermocouple over the entire length scale of the thermocouple, not just the temperature at the measurement node.
8. Short-term stability
Measuring repeatability is a term that can be used in a number of different ways. It should be said by the community of people who use the term. It generally refers to the repeatability of RTPW during thermal cycling or calibration.
|
More on that
|
Analysis of the humidity sensor product – Turck
In the domestic market, there are many domestic and foreign humidity sensor products, capacitive moisture-sensitive components are more common, and the varieties of moisture sensing materials are mainly polymers, lithium chloride and metal oxides.
The advantages of capacitive moisture sensitive elements are ...
|
|
Turck proximity sensors and their models
Turck's proximity sensors, also known as contactless proximity switches, are ideal electronic switching sensors. When the metal detector is close to the sensing area of the switch, the switch can be contactless, pressure-free, non-sparking, and issue electrical commands, accurately reflecting the position and stroke of the moving mechanism, even if it is used for a ...
|
|
Choice of temperature sensors – Turck
(1) Whether the temperature of the measured target needs to be recorded, alarmed and automatically controlled, and whether it needs to be measured and transmitted at a distance.
(2) The size and accuracy of the temperature measurement range.
(3) Whether the size of the temperature measuring element is appropriate.
(4) Tested ...
|
|
The load cell of the mixing plant was selected by Turck
The selection of load cells mainly includes the following four aspects, namely, the sensitivity of the sensor, the accuracy of the sensor, the stability of the sensor, and the number and range of the sensor.
1. Sensitivity
Usually, in the ...
|
|
Sensor technology boosts the development of the robotics industry – Turck
Since the beginning of the 60s, China has made great progress in the research and development, design, production, and reliability improvement of sensors after the national research and development from the "Sixth Five-Year Plan" to the "Ninth Five-Year Plan", and has initially formed a system of sensor research, development, production and use.
|
|
Turck has received two more awards at CAIMRS 2021
On March 19, 2021, the 2021 CAIMRS and Annual Selection and Awards Ceremony of China's Production Digital Service Summit hosted by Industrial Control Network was held in the form of real-time live broadcast in the cloud, and the results of the 19th Automation and Digitalization Annual Selection were released. Turck has once again been named one of the "Top 10 Companies of the Year".
|
|
Turck sensor technology
1. Capacitive pressure sensors are usually loved by many OEMs to test the capacitance changes between the two appearances, so that the sensors can sense extremely low pressure and vacuum levels. In our typical sensor configuration, the tight shell consists of two golden appearances, metal ...
|
|
Characteristics of strain gauge load cells and piezoresistive effect – Turck
As the main force measurement sensor, the force measurement scale of strain resistance sensors varies from muscle fibers to moon rockets, and the accuracy can reach 0.01%-0.1%. There are tensile types (in, tube, ring), zigzag and shear. Features of strain sensors:
...
|
|
Turck's BL ident with long-range UHF technology
BL ident products with long-interval UHF technology from Turck can be used in product control, logistics or process automation systems. Compared to HF, UHF has a longer read/write interval. UHF modules can be sensitively integrated into the BL ident system without the need for messy equipment ...
|
|
What is an SOI high-temperature pressure sensor – Turck
Pressure sensor is a kind of equipment used to detect pressure signals and convert pressure signals into electrical signals according to certain rules, which are widely used in various production, industry and aerospace fields. With the subdivision of application fields, the pressure in high-temperature and harsh environments such as high-temperature oil wells and various engine cavities ...
|
|
Turck's newer, faster I0-Link encoder
Turck's encoder series has been strategically expanded even further. We can now consider our customers to offer newer and faster encoders with IO-link interfaces.
Expansion of the product range
As part of Turck's product range ...
|
|
Common faults in temperature sensors – Turck
First, there is no change in the output of the transmitter when the temperature of the measured medium rises or decreases.
This situation is mostly a problem with the sealing of the temperature sensor, which may be because the temperature sensor is not sealed well, or it may be that the sensor is accidentally welded into a small hole during welding.
|
|
Turck's IM34 temperature changeover combines the advantages of a single device
Temperature measurement is a common application, even in hazardous areas. IM34 temperature conversion equipment is a high-end diagnostic device, with comprehensive functions, convenient use and easy operation.
The IM34 is capable of bringing 2, ...
|
|
Three-wire connection for proximity switches – Turck
There is a difference between the two-wire system and the three-wire system of the proximity switch, and the three-wire system proximity switch is divided into NPN type and PNP type, and their wiring is different.
The wiring of the two-wire proximity switch is relatively simple, and the proximity switch is connected in series with the load.
|
|
Are AC and DC contactors interchangeable?
1. The AC contactor can be used as a substitute for the DC contactor in an emergency, and the suction time can not exceed 2 hours (due to the poor heat dissipation of the AC coil than the DC, which is determined by their different structures).
|
|
Turck's IO-LINK junction box with 16 universal channels
Turck has added a new member to its IO-link junction box portfolio with 16 universal channels (digital input or output).
Turck presents a new I/O junction box with 16 universal channels.
|
|
Precautions for the installation of load cells in Turck
First of all, when using load cells, it is necessary to adjust the orientation of the sensors. Think of the sensor as a fragile product, cut the oscillation of the sensor, and try to handle it gently, because many sensors have elastomeric devices planned internally, and these elastomeric devices are critical to the stability of the sensor, ...
|
|
Turck temperature and humidity online monitoring sensor
Turck presents sensors for online monitoring of temperature and air humidity for online monitoring of the Industrial Internet of Things and sensor-to-cloud use.
Composite air humidity/temperature sensor for field or industrial IoT ...
|
|
Triangulation principle for photoelectric sensors – Turck sensors
So what is right and wrong color aberration? To put it simply, it is an ordinary diffuse reflex sensor, for example, if you set punctuality to learn a black object, assuming that the sensing interval of the black object is set to 50 mm, then when the sensor detects a white object, the practical action interval may reach 80 mm, which ...
|
|
Turck Potentiopotential Isolated HART Module
The new HART modules for Turck's excom I/O system are faster, more reliable in signal transmission and can be used at temperatures up to 70°C
Turck presented the new HART module for the excom I/O system. The module has a fully resistively isolated channel, so it prevents the ring and ground currents from being ...
|
|
Contact
working hours
