Warum sind Ihre Temperaturkammer-Testergebnisse immer instabil?

Issues with the Equipment Itself

• Calibration and Accuracy

• 1. Problem: After long-term use, temperature sensors and control systems may drift, causing systematic deviations between the actual temperature and the setpoint.
  2. Troubleshooting & Recommendation: Verify whether the equipment has been regularly calibrated by a qualified institution as scheduled (typically once a year, but the cycle should be adjusted based on usage intensity and quality management requirements). Keep calibration records, certificates, and environmental conditions during calibration properly archived.
• Sensor Placement
  1. Problem: The controller typically reads temperature from a fixed point inside the thermostatic chamber (e.g., near the return air vent). If the sample is large, generates heat, or is placed away from airflow inlets/outlets, the actual local temperature may significantly differ from the control point.
  2. Troubleshooting & Recommendation: Check whether the control sensor is blocked or affected by local heat sources. For self-heating or high thermal-mass samples, use independent monitoring sensors near the sample to verify its actual temperature (and document any discrepancies).
• PID Steuergerät Parameter
  1. Problem: PID (Proportional–Integral–Derivative) parameters determine how the system responds to deviations. Improper PID settings may cause large oscillations around the setpoint (overshoot or undershoot) or result in delayed recovery.
  2. Troubleshooting & Recommendation: If test conditions (e.g., load size, sample thermal characteristics, or desired temperature ramp rate) change, PID parameters should be reassessed and retuned. Perform tuning under controlled conditions and compare pre- and post-tuning curves. Seek support from the manufacturer or experienced engineers if necessary.
• Mechanical System Issues
  1. Heater: Aging or faulty connections can cause unstable heating power.
  2. Kompressor: Refrigeration failures (e.g., refrigerant leakage, reduced compressor efficiency) result in insufficient cooling, especially at low-temperature ranges.
  3. Kondensator: Dust buildup in air-cooled condensers or scaling in water-cooled condensers lowers heat exchange efficiency, impairing cooling performance.
  4. Door Seals: Aging or damaged gaskets allow external air to leak in, disturbing temperature and humidity control.
  5. Troubleshooting & Recommendation: Conduct visual and operational checks (e.g., inspect condenser cleanliness, listen for abnormal compressor noise, check seal integrity). Address abnormalities promptly with maintenance or replacement and record all service activities.

Test Methodology and Sample Influences

• Sample Load
  1. Problem: Chambers are designed for a specific volume and thermal load. Excessive sample size or thermal capacity (commonly recommended not to exceed one-third of the chamber’s volume), or samples with significant heat dissipation or generation, can severely disrupt the internal temperature distribution.
  2. Troubleshooting & Recommendation: Assess whether sample volume, weight, and power consumption are within the equipment’s design limits. Refer to the user manual or load specifications to adjust accordingly.
• Sample Placement and Airflow
  1. Problem: Improper sample placement may obstruct airflow, creating uneven temperature zones and causing different parts of the sample to experience different conditions.
  2. Troubleshooting & Recommendation: Ensure sufficient spacing between samples and from thermal chamber walls (typically >10 cm). Avoid blocking airflow inlets/outlets. Use shelves or racks with open structures to maintain ventilation.
• Wiring and Feedthroughs
  1. Problem: Numerous external cables (e.g., power or signal lines) can act as thermal bridges, transferring heat in or out and compromising chamber sealing.
  2. Troubleshooting & Recommendation: Minimize the number and thickness of external cables. Use designated feedthroughs and seal gaps with insulation or sealing materials to reduce heat leakage and air exchange.

Environmental and Operational Factors

• Ambient Conditions

• 1. Problem: If the chamber is placed in a high-temperature or poorly ventilated environment, heat dissipation is restricted, increasing system load. Prolonged operation under such stress may trigger protective shutdowns.
  2. Troubleshooting & Recommendation: Maintain adequate clearance around the chamber for heat dissipation (e.g., larger spacing at the back, gaps on both sides). Keep laboratory ambient temperature within the specified operating range (commonly 5°C–30°C, as per the manual).
• Test Program Setup
  1. Problem: Improper test programming—such as not allowing enough soak time after reaching the target temperature—may cause the sample’s internal temperature to be incorrectly judged as stable.
  2. Troubleshooting & Recommendation: Include sufficient stabilization time at each setpoint. Define appropriate tolerance windows (e.g., ±0.5°C, depending on standards and chamber performance). Ensure the sample has reached equilibrium before timing or moving to the next step.

Recommended Systematic Troubleshooting Steps

• Empty Chamber Test Run a standard program without samples (e.g., ramp from ambient to target and hold for several hours). Place calibrated independent loggers at multiple points inside the chamber. If distribution is stable and uniform, the equipment is likely sound, and the issue may stem from load or method.
• Simplified Test If empty chamber results are stable, use a standard thermal load (e.g., metal blocks or calibrated thermal mass) to verify stability and determine whether the issue is sample-related.
• Review Logs Modern chambers often record alarms and historical curves. Carefully review events during instability (e.g., overload, overtemperature protection) and analyze compressor/heater runtime curves to correlate anomalies with specific timeframes.
• Contact Technical Support If issues remain unresolved, document the instability in detail (e.g., fluctuation amplitude, frequency, affected temperature ranges, uniformity vs. overshoot issues). Submit this data along with test curves, maintenance records, and calibration certificates to the manufacturer or an authorized service provider for faster diagnosis and repair.

Schlussfolgerung