Table of Contents

1. Introduction

2. The Importance of Material Temperature Monitoring

3. Types of Sensors and Working Principles

4. Principles of Sensor Layout

5. Number and Distribution of Temperature Measurement Points

6. Sensor Accuracy Control and Calibration Methods

7. Transmission of Collected Signals and Data Processing

8. Case Study of High-Precision Monitoring System Design

9. Impact of Temperature Anomalies on Mixture Performance

10. System Maintenance and Common Problem Analysis

11. Conclusion

Main Text

1 Introduction

Temperature control of asphalt mixtures is a core indicator for ensuring pavement quality. If the mixture temperature is too low, it can lead to insufficient asphalt coating, affecting bonding performance and resistance to rutting; if the temperature is too high, it may damage the asphalt structure and reduce durability. The role of the material temperature monitoring system is to real-time and accurately collect temperatures at various stages, providing a scientific basis for quality control of the mixture.

2 The Importance of Material Temperature Monitoring

The core functions of material temperature monitoring include:

• Real-time feedback of aggregate temperature at the dryer drum outlet

• Control of asphalt heating temperature and flow rate

• Support for optimization of mixing time and speed

• Ensure uniform heating of recycled materials

• Prevent overheating or low temperature of the mixture

Temperature fluctuations directly affect the stability, segregation, and compaction of the mixture, thus requiring high monitoring accuracy, generally ±1–2℃.

3 Types of Sensors and Working Principles

3.1 Thermocouples

• Materials: Nickel-chromium, nickel-silicon, etc.

• Features: Fast response, high-temperature resistance, flexible installation

• Disadvantages: Limited accuracy (±1–2℃), requires regular calibration

3.2 Platinum Resistance Temperature Detectors (RTD)

• Materials: Platinum wire

• Features: High accuracy (±0.1–0.5℃), good linearity

• Disadvantages: Relatively slow response, sensitive to environmental vibrations

3.3 Infrared Thermometers (Non-contact)

• Suitable for rapid measurement of surface temperature of aggregates at the dryer drum outlet

• No direct contact required, high temperatures up to 600℃

• Note measurement aperture, emissivity settings, and dust prevention measures

4 Principles of Sensor Layout

Reasonable layout ensures data accuracy, with the following principles:

1. Mainstream Material Area Layout: Preferred points are where aggregates flow, avoiding stagnant or dead zones.

2. Temperature Gradient Coverage: Sensors are arranged at different material layers and heights to obtain temperature distribution information.

3. Avoid Thermal Interference: Keep away from flames, steam outlets, and other localized high-temperature points to prevent high measurements.

4. Redundant Layout: Set up backup sensors at critical nodes to improve reliability.

5 Number and Distribution of Temperature Measurement Points

• Dryer drum outlet: 2–3 points on average

• Mixing tower entrance: 1–2 points

• Asphalt tank outlet: 1 point

• Mixture discharge outlet: 2–3 points

Multi-point collection can reduce the impact of single-point errors on overall control, achieving ±1℃ accuracy control.

6 Sensor Accuracy Control and Calibration Methods

• Regular Calibration: Use standard temperature furnaces or calibration instruments to correct thermocouples and platinum resistance sensors

• Measurement Environment Compensation: Consider the impact of cable length and ambient temperature on sensor readings

• Signal Filtering: Filter out instantaneous fluctuations through PLC or data acquisition systems

• Regular Replacement of Aging Sensors: Prevent drift caused by prolonged high temperatures

7 Transmission of Collected Signals and Data Processing

Temperature signal transmission mainly uses:

• Analog signals (4–20 mA)

• Digital signals (RS485, Modbus, CAN bus)

Data processing logic:

1. Signal collection → PLC or DCS system

2. Average calculation → feedback temperature control

3. Abnormal alarm → automatic adjustment of heating, pumping, or shutdown protection

8 Case Study of High-Precision Monitoring System Design

A large asphalt mixing plant:

• Three infrared temperature measurement points arranged at the dryer drum outlet

• Two platinum resistance probes arranged at the mixing tower entrance

• Contact thermocouples added at the mixture discharge outlet

• PLC automatically calculates average temperature and adjusts asphalt pump flow rate

• Achieves temperature stability of ±0.8℃, with mixture uniformity exceeding 95%

9 Impact of Temperature Anomalies on Mixture Performance

• Too Low Temperature: Thin asphalt film, severe segregation, poor compaction

• Too High Temperature: Reduced asphalt viscosity, easy to stick to walls, decreased durability

• Excessive Temperature Difference: Uneven bonding of different material segments, affecting mixing uniformity and gradation stability

Therefore, the material temperature monitoring system must closely coordinate with asphalt supply, mixing time, and mixture transportation.

10 System Maintenance and Common Problem Analysis

Common issues include:

• Sensor drift: Long-term high temperatures or vibrations lead to errors

• Loose connections: Cause signal loss

• Dust coverage: Blockage of infrared measurement ports, leading to low readings

• Frequent abnormal data alarms

Maintenance methods:

• Regularly clean measurement ports

• Calibrate sensors and replace aging components

• Check wiring and communication lines

• System upgrades and software filtering optimization

11 Conclusion

The material temperature monitoring system is a crucial part of ensuring the quality of mixtures and optimizing processes at asphalt mixing plants. Through scientific layout, multi-point collection, and high-precision sensors along with reliable data processing, it can significantly enhance mixture uniformity, compaction, and pavement durability. At the same time, precise temperature control is also an important guarantee for energy saving and extending equipment lifespan.