Industrial fire monitoring temperature sensor

1 Overview

control cabinetTemperature sensor for supporting electrical fire monitoring deviceAlso known as a negative temperature coefficient sensor, it utilizes the physical property of the NTC thermistor that the resistance value rapidly decreases with the increase of temperature, and senses temperature changes by measuring the changes in its resistance value. In the field of electrical fire safety, it can be used to monitor the temperature of energized cables or distribution boxes, achieve temperature measurement and control, and thus protect the safety of electrical appliances, personnel, and property.

Product compliesGB14287.3-2014《Electrical Fire Monitoring System3part:temperature measurementElectrical fire monitoring detectorofmarkStandard requirements.

2 Installation methods

The installation method of NTC temperature sensor is fixed installation. During installation, the temperature probe can be tightly attached to the surface of the cable, busbar or cable joint, and fastened with nylon zip ties. In addition, according to customer needs, the temperature probe can also be suspended or tightly attached to the cabinet to measure the temperature of the environment or cabinet.

3 Error analysis

During the process of the resistance value of NTC temperature sensors changing with temperature, errors may occur within a certain range due to the influence of their accuracy. During the measurement process, errors are inevitable due to differences in the use of instruments and connection lines. This includes the error of sensors on the graduation table; Errors caused by poor insulation; Error caused by line resistance; Interference errors, etc.

4 Application principles and related interfaces

Our customized NTC temperature sensor is applied to our electrical fire monitoring detector. Monitor the temperature of the distribution box, cables, or cable connections through temperature sensors. When the temperature exceeds the set value, delay for a certain period of time to trigger an alarm or disconnect the circuit breaker. During the delay process, if the temperature value drops below the set temperature value, the delay will reset to zero and will not take any action. The detector can display the temperature value of the detected object in real time and automatically adjust the circuit based on the temperature value, achieving a dual combination of monitoring and control, providing strong guarantee for electrical safety.

Principle of industrial fire monitoring temperature sensor:

1. Thermal effect

• NTC thermistorThe resistance value decreases with increasing temperature (negative temperature coefficient), commonly used for medium and low temperature monitoring (such as -40 ℃~+150 ℃), with fast response speed (millisecond level), but high nonlinearity, requiring circuit compensation.

• PTC thermistorThe resistance value increases with temperature (positive temperature coefficient), commonly used for overcurrent protection or high temperature limiting, and is less commonly used in fire monitoring.

2. thermoelectric effect

• thermocoupleComposed of two different metals (such as K-type: nickel chromium nickel aluminum), the temperature difference is converted into millivolt level voltage signals through the Seebeck effect, suitable for high temperature monitoring (such as 0 ℃~+1300 ℃), but with low sensitivity (about 40 μ V/℃), requiring an external signal conditioning circuit.

3. Semiconductor effect

• Digital temperature sensorFor example, DS18B20 (Dallas Semiconductor) integrates temperature sensitive components, A/D converters, and digital interfaces (1-Wire protocol), which can directly output digital signals with high accuracy (± 0.5 ℃) and moderate range (-55 ℃~+125 ℃), suitable for distributed monitoring.

4. infrared thermography

• Non contact monitoringBy detecting the infrared energy (wavelength 8-14 μ m) radiated by objects, temperature distribution images are generated, which is suitable for large-scale and remote monitoring (such as warehouses and substations), but the cost is relatively high (tens of thousands of yuan per device).