Temperature Sensor Calibrations in Weathering and Corrosion Testing

At Q-Lab, our weathering and corrosion test chambers are engineered to simulate the real-world conditions that products encounter, exposing materials to stressors such as heat, light, and moisture. Properly-calibrated onboard temperature sensors are critical for accurate temperature control during testing. In this blog, we’ll explain why some temperature sensors can be calibrated using a hot water bath, while others require a specially-calibrated black panel reference sensor.

Temperature Sensor Calibration Using a Reference Thermometer

Many Q-Lab testers use sensors that can be calibrated with a standard reference thermometer. This includes chamber air temperature (CAT) sensors (used in the Q-FOG, QCT, and optionally in the Q-SUN Xe-1), panel temperature sensors (used in the QUV, sometimes referred to as Black Panel), and wet/dry bulb thermometers (used in the Q-FOG CRH). The process for calibration is simple & straightforward:

1. An insulated container (Fig. 1) is filled with water of approximately the highest temperature called for in the test cycle of interest.
2. A calibrated reference thermometer and the tester’s temperature sensor are both placed in the container, nearby each other.
3. After the temperature has stabilized, the value from the calibrated reference thermometer is communicated to the tester via the tester's user interface.

Figure 1. Insulated calibration container with reference thermometer and onboard temperature sensor

This method works well for the sensors listed above because they measure temperature through thermal conductivity. However, this technique is not suitable for Q-SUN black panel (BP) or insulated black panel (IBP) thermometers.

Why do Q-SUN Black Panel Thermometers Require Special Calibration?

Unlike the temperature sensors described previously, uninsulated and insulated black panel temperature sensors in the Q-SUN (Fig. 2) primarily heat up by absorbing radiant energy from ultraviolet (UV), visible, and infrared (IR) light from the xenon arc lamps, while also losing heat through convection to chamber air. This leads to two effects:

• Color Temperature Differences: A black panel absorbs more light energy than a white panel, leading to significant temperature differences (up to 14°C in xenon arc testers).
• Thermal Conductivity: Imperfect heat transfer between the panel’s surface and the internal sensor creates a temperature delta.

Figure 2. Onboard and calibration Unisulated Black Panel sensors

These factors make the calibration of black panel thermometers more complex, as a water bath cannot replicate the radiant heat or convective cooling they experience during operation. Q-SUN BP and IBP sensors are calibrated using a UC202/BP or UC202/IBP Temperature Smart Sensors (Fig. 3), which are specialized black panel sensors designed to measure radiant heat and convective cooling in air. Effectively, they are calibrated versions of the same onboard sensors used in Q-SUN xenon arc testers. The appropriate calibrated UC202 sensor is placed next to the onboard BP or IBP temperature (Fig. 2), the tester is allowed to stabilize at operating temperature, and the calibrated reading is transferred to the tester using Q-Lab's AUTOCAL system. This ensures accurate temperature readings under real test conditions.

Figure 3. UC202/BP and UC202/IBP Temperature Smart Sensors for Calibration

Specialized Calibrations

There are two temperature sensor calibrations in Q-Lab equipment that differ from the two methods described previously.

1. The chamber air temperature (CAT) sensors used in Q-SUN Xe-2 and Q-SUN Xe-3 testers (Fig. 4) cannot be adjusted during calbration, so users are required to replace the onboard RH/CAT annually with a freshly calibrated sensor.

Figure 4. Onboard RH/CAT sensor in a Q-SUN Xe-3 xenon arc tester

2. The black panel in the Q-SUN Xe-1-WE is an exception to the Q-SUN black panel calibration scheme described above. Since the BP is located in the ponding tray during immersion steps, where the black panel temperature measured is primarily thermal conductivity with the water instead of absorbed radiant energy, it is calibrated using a reference thermometer placed in the ponding tray during a Dark+Immersion step.

Conclusion

Proper calibration of onboard temperature sensors ensures that your Q-Lab tester delivers consistent, repeatable results. Because of the different conditions they experience during testing, different onboard temperature sensors in QUV and Q-SUN testers are calibrated using different procedures - a hot water bath or a calibrated black panel thermometer, as appropriate.

Do you have questions on recalibration? Our team of experts is here to help. Click the button below to get in direct contact with our team today!

Contact Us