As a high-precision device for testing the thermal and physical properties of materials, the optical thermal expansion instrument requires a coordinated optimization of mechanical accuracy, optical alignment, and temperature control during its debugging process. The following is a systematic debugging process and key technical points:
1、 Basic environment and equipment inspection
1. Environmental adaptation: Place the instrument in a constant temperature and humidity laboratory (recommended temperature fluctuation ≤ ± 0.5 ℃/hour), away from vibration sources (such as centrifuges) and strong electromagnetic interference areas. Ensure that the levelness of the workbench is better than 0.1mm/m, and use a precision level to calibrate if necessary.
2. Component integrity verification: Check whether the laser emitter, photoelectric receiver, sample holder, heating furnace body, and temperature control module are intact, with a focus on confirming that the optical window is clean and free of scratches, and that the fiber optic interface is not loose.
3. Power supply and grounding: Independent power sockets are used to ensure reliable grounding of the equipment casing and prevent static electricity accumulation from affecting the stability of optical signals.
2、 Accurate calibration of optical systems
1. Initial optical path alignment: After turning on the laser source, adjust the relative position of the transmitter and receiver through the observation screen, so that the laser beam is vertically incident on the center of the reflective mirror on the sample surface. Use a small aperture stop to assist in positioning, ensuring that the beam path coincides with the axis of the sample.
2. Dynamic feedback adjustment: Place a standard zero expansion ceramic plate as a reference sample and activate the automatic tracking mode. Monitor the light intensity curve in the software interface and fine tune the pitch/yaw knob until the light intensity reaches its peak and fluctuates by less than 1%.
3. Multi level amplification verification: Switch objective lenses of different ranges to verify the consistency of linear response at each gear. Pay special attention to the depth of field range of high magnification lenses to avoid data jumps caused by defocus.
3、 Configuration of temperature control system
1. Temperature control program loading: Set the heating rate (typical value 1-5 ℃/min), target temperature range, and insulation time based on the characteristics of the tested material. It is recommended to use no-load operation for debugging and record the deviation curve between the actual furnace temperature and the set value.
2. Thermal equilibrium verification: Place a thermocouple inside the sample chamber and compare the displayed temperature with the measured temperature difference. If the deviation exceeds ± 1 ℃, the PID parameters need to be recalibrated or the uniformity of the heating wire distribution needs to be checked.
3. Cold and hot shock test: Perform rapid temperature rise and fall cycles (such as room temperature → 200 ℃ → room temperature), observe the drift of the optical system at special temperatures, and evaluate thermal stability.
4、 Sample loading and parameter optimization
1. Sample preparation specifications: The parallelism of both ends of the processed sample is less than 0.01mm, the surface roughness Ra is less than or equal to 0.8 μ m, and a thermocouple is attached to the non measuring surface to monitor the real temperature in real time.
2. Contact pressure control: Slowly lower the probe to lightly touch the sample, and maintain a slight preload force (usually 0.1-0.3N) through the displayed value of the force sensor to avoid excessive compression and stress deformation.
3. Baseline deduction operation: Collect raw length data as a benchmark during the unheated stage, and automatically deduct this initial value from subsequent measurements to eliminate mechanical clearance errors.
5、 Data Collection and Exception Handling
1. Sampling frequency matching: Adjust the data acquisition interval based on the heating rate (generally no less than 10 valid data points per minute), and increase it to once per second during the high-speed expansion stage.
2. Noise suppression strategy: Enable hardware filtering function to eliminate high-frequency interference, and use moving average method to smooth the curve on the software end. If there are periodic fluctuations, it is necessary to investigate the resonance interference of air conditioning supply or lighting equipment.
3. Fault diagnosis process: When encountering data abnormalities, check for issues such as light path obstruction, temperature overshoot, and sample oxidation in sequence. The typical manifestation is that the sudden rise curve indicates sample melting and adhesion, while the stepped decline is caused by thermal shock cracking.
Through the above phased debugging, the optical thermal expansion instrument can achieve sub micron level measurement accuracy. In practical applications, it is necessary to establish exclusive testing protocols based on specific material systems, regularly conduct standard sample traceability calibration, and ensure long-term measurement reliability.