Temperature sensing cable type temperature measurement. Place the temperature sensing cable in parallel with the cable. When the temperature of the cable exceeds a fixed temperature value, the sensing cable is short-circuited and an alarm signal is sent to the control system. The disadvantages of ordinary temperature sensing cables are: destructive alarms, fixed alarm temperature, incomplete fault signals, system installation and maintenance are not convenient enough, and equipment is easily damaged; analog linear temperature sensing cables can only use a certain partial line as the alarm unit , So it cannot accurately locate the alarm signal generated at a certain point.
Thermistor temperature measurement. The thermistor can be used to measure the temperature value of the cable, but they are all analog outputs, which require signal amplification and A/D conversion to be received. Each thermistor needs independent wiring, the wiring is complicated and the thermistor is easy Damaged, large amount of maintenance, the sensor does not have the self-checking function, needs to be checked frequently.
Infrared sensor temperature measurement. Infrared sensing uses all objects whose temperature is higher than absolute zero to continuously emit infrared radiation energy to the surrounding space. The size of the infrared radiation energy of an object and its wavelength distribution are closely related to its surface temperature. Therefore, by measuring the infrared energy radiated by the object itself, its surface temperature can be accurately determined. Infrared sensor is non-contact measurement, so it has good safety. Its disadvantage is that it is greatly affected by object emissivity, environment and aerosol during temperature measurement, and its anti-interference ability is poor.
Thermocouple type temperature measurement. The thermocouple transmission signal needs to use a special compensation line, and the transmission distance should not be too long, and it is not suitable for the actual situation of a wide distribution of the cable head; the thermistor is usually a platinum resistance, and generally requires three-wire transmission, balanced bridge output, The transmission distance should not be too long, and the anti-interference ability is poor.
Integrated circuit temperature measurement. There are many types of integrated circuit-type temperature measuring components. Among them, the current output type component has a large internal resistance and is suitable for long-distance transmission. It is usually small in size and can be sealed at the measured point with anti-corrosion, moisture-proof and high-temperature thermal conductive silica gel. , The external wiring is led out by two wires to transmit data, but it is greatly affected by electromagnetic at the measured point.
Optical fiber distributed temperature monitoring. The optical fiber distributed temperature measurement system is a more advanced system. The temperature measurement is completed by the back Raman scattering temperature effect of the laser pulse transmitted in the optical fiber. The latest optical fiber distributed temperature monitoring system can allow the length of the optical fiber loop to reach 12 km and the measurement accuracy to ±1°C. The advantage of using the optical fiber distributed temperature monitoring system is that it can locate the hot spot position along the cable with high precision, can display and record the temperature change curve track, and can show the position of the hot spot on the line. This kind of system is required to be able to determine the location of the hot spot during installation, but it relies on pre-manufactured monitoring equipment and optical/thermal data processing, which not only increases additional equipment investment, but the newly added equipment also faces maintenance problems.
