Temperature-sensitive cable temperature measurement. The sensitive cable is placed in parallel with the cable, and when the cable temperature exceeds the fixed temperature value, the sensing cable is short-circuited and an alarm signal is issued to the control system.
The disadvantages of ordinary temperature-sensitive cable are: destructive alarm, alarm temperature fixed, fault signal is not complete, system installation and maintenance work is not convenient, equipment is easy to damage; analog linear temperature-sensitive cable can only take a certain local line segment as the alarm unit, so it can not accurately locate the alarm signal generated by a certain point. Thermistor type temperature measurement.
The use of thermistors can measure the temperature value of the cable, but are analog output, the need for signal amplification and A/D conversion to be received, each thermistor needs a separate wiring, complex wiring and thermistor easy to damage, large maintenance, the sensor does not have self-test function, need to check frequently. Infrared sensor temperature measurement. Infrared sensing is the use of all the temperature above the absolute 0 degrees of objects are constantly emitting infrared radiation energy to the surrounding space, the size of the object's infrared radiation energy and its distribution by wavelength and its surface temperature has a very close relationship. Therefore, by measuring the infrared energy of the object's own radiation, it can accurately determine its surface temperature.
Infrared sensing is a non-contact measurement, so it has a good safety, the disadvantage is that in temperature measurement by the object emissivity, environment and aerosol influence is greater, anti-jamming ability is poor. Thermocouple type temperature measurement.
Thermocouple Transmission signal needs special compensation line, and transmission distance should not be too long, does not adapt to the wide distribution of cable head of the actual situation; thermistors are usually platinum resistors, generally need to use third-line transmission, balanced bridge output, transmission distance should not be too long, and the ability to resist interference is poor. IC type temperature measurement.
Integrated circuit type temperature measuring elements have a variety of types, of which the current output type of components have a large internal resistance, suitable for long-distance transmission, usually small size, can be used anti-corrosion and moisture-resistant high-temperature thermal conductive silicone seal at the measuring point, the outer wiring from two lines to transmit data, but at the measured point by electromagnetic influence. Optical fiber distributed temperature monitoring. Optical fiber distributed temperature measurement system is a more advanced system. The temperature measurement is accomplished by the Raman scattering temperature effect after the laser pulse transmitted in the fiber is generated. The latest fiber-optic distributed temperature monitoring system allows the fiber circuit to reach a length of km, measuring accuracy of ±1°c. The advantage of using optical fiber distributed temperature monitoring system is that the hotspot position along the cable can be positioned with high precision, which can display and record the trajectory of temperature change curve, and can show the position of hot spot on the line. This system requires the ability to determine the location of hot spots at the time of installation, but relies on pre-manufactured monitoring equipment and optical/thermal data processing, which not only increases the investment in additional equipment, but also faces maintenance problems for the newly added equipment.