Q: Why does dew condense on the surface of the water-cooled power meter?
A: The core reason is that the surface temperature of the probe is lower than the dew point temperature of the ambient air.
When the cooling water temperature is set too low, or the environmental humidity is high, the temperature of the probe housing, absorption surface, window and other parts is lowered to below the dew point by the water cooling system, and the water vapor in the air will condense into liquid water droplets when encountering cold surfaces.
Special attention is needed:It's not because the water cooling temperature is very low that dew can condense. When the ambient humidity is high, even if the water cooling is set at 20-22℃, dew may still condense.
Q: How do the structural characteristics of water-cooled thermoelectric power meters affect dew condensation?
A: The structure of water-cooled thermoelectric power meters naturally carries a "cold surface" risk.
The absorber is closely attached to the water-heat exchange substrate, and water cooling directly presses its temperature to a very low level. The surface of the probe housing, protective window, and absorption layer directly contact the indoor ambient air. The thermoelectric material itself is a thermally resistive structure-the absorption surface heats up when irradiated by laser light, but the water-cooled substrate continues to be low, and the metal shell and window are conducted by the water-cooled substrate to cool down.
This combination of "cold surface + high humidity air" is the fundamental cause of dew condensation.
Q: What are the common causes of dew condensation in water-cooled power meters?
A: There are four main inducements:
① Cooling water temperature is set too low (most common)
In high-power test scenarios, operators are accustomed to setting the chiller temperature to 10-15 ° C in pursuit of lower probe temperature rise. However, when the environmental humidity is>50%RH, especially in the plum rainy season or southern summer, the dew point at room temperature of 25-28 ° C is often higher than 16-18 ° C, and the probe housing is cooled below the dew point and dew is immediately condensed.
② The relative humidity of the ambient air is too high
The humidity in the workshop is not controlled, the rainy season, the equipment is always open, and the risk of dew condensation increases sharply when the environmental humidity is greater than 60% RH. Even if the chiller is set to 20 ° C, dew will still condense in a high-humidity environment.
③ Probe sealing failure (most dangerous)
Water-cooled thermoelectric probes rely on sealing rings to achieve sealing. If the water quality is poor or the sealing ring is corroded, aged and seeps water, it will directly contaminate the surface of the probe absorption film. Dewing condensation on the film is difficult to detect at the first time. The adhesion of water droplets to the film will produce a focusing effect. The laser irradiation will cause local overheating and easily burn the probe.
④ Temperature dynamic changing conditions
When the chiller is turned on, the probe cools down quickly, and the ambient temperature has not yet been synchronized, resulting in short-term overcooling. In the intermittent working mode, there is no heat input after the laser is turned off, and the water cooling continues to cool, and the overall temperature of the probe further drops, making it easier to condense dew. After the laser is turned on, the absorption surface is heated, and the water droplets quickly evaporate, causing the reading to jump.
Q: What practical hazards will dew condensation bring?
A: The harm of dew condensation to the power meter is systematic, and it will be seriously affected from measurement accuracy to hardware life.
1. measure anomalies
Water droplets adhere to the surface of the probe, which is equivalent to a micro lens, causing light spots to converge and an abnormal increase in power density. Uneven light absorption directly causes reading drift, poor repeatability, and greatly reduces the credibility of measurement data.
2. device damage
The water droplets and the high heat of the laser act together to produce local thermal shocks, causing foaming and peeling of the absorbing coating, causing permanent damage to the probe.
3. electrical risks
Condensate water flows into the cable connectors along the housing, which may cause signal short circuits and abnormal thermopile output.
4. secondary corrosion
In a long-term dew condensation environment, the metal base and seal rings are corroded, accelerating seal leakage, forming a vicious cycle-the more dew condensation, the worse the seal, and the worse the seal, the easier it is for water to enter.
Q: How to suppress dew condensation through chiller settings?
A: The core principle is to increase the cooling water set temperature to be higher than the environmental dew point.
Practical operation principle: Cooling water outlet temperature ≥ environmental dew point +2 ℃-3℃ safety margin.
Don't blindly pursue low temperatures! The core function of a water-cooled thermoelectric power meter is to take away the temperature rise caused by the laser, rather than freezing the probe to a low temperature. Too low the water temperature will amplify the risk of dew condensation.
For example: When the ambient temperature is 26 ° C and the humidity is 60%RH, the dew point is about 17.6 ° C. At this time, increase the set temperature of the chiller to more than 20℃ to reserve a safety margin to avoid touching the dew point.
Other chiller optimization measures:
Turn on closed-loop temperature control to avoid excessive cooling when there is no laser load
In the intermittent test scenario, when the laser output stops, the water temperature can be raised moderately or the cooling can be turned off for a short time, and only water circulation can be maintained.
Note: Increasing the water temperature will cause a small increase in the overall temperature rise of the probe under laser irradiation. The maximum operating temperature allowed in the probe specifications needs to be checked, and it is not allowed to exceed the specifications.
Q: In addition to adjusting the chiller, what other methods can we prevent dew condensation?
A: You can start through both environmental improvement and hardware sealing inspection.
Environmental conditions have improved
Control the humidity in the workshop and try to control the environmental RH to30-50%RH
Dehumidifier is equipped in high-humidity environments, and key control is carried out during the plum rainy season.
Avoid blowing the probe directly into humid airflow. Do not blow the probe directly into workshop doors and air conditioner outlets
Avoid violent fluctuations in ambient temperature and reduce dew point changes caused by temperature differences between day and night
Probe hardware and sealing inspection
Regularly check the surface of the power meter film for water seepage. If it is found that the sealing ring has been corroded causing water seepage,Use of the probe should be stopped immediately, return it to the factory for maintenance and replacement of the sealing ring, and do not continue to test on the machine-otherwise, it will easily burn the absorber.
Q: How to fundamentally solve the dew condensation problem?
A: It is necessary to establish a long-term mechanism from both aspects of constant temperature and humidity environment and standardized operation and maintenance operations.
Constant temperature and humidity environment
Control the environmental temperature at a constant temperature to prevent fluctuations in the temperature difference between water cooling and the environment due to temperature changes, and fundamentally reduce the risk of condensation. Equipped with a dehumidifier to control the environmental humidity within the safe range of 30- 50% RH.
Operation and maintenance operation specifications
Boot sequence: Turn on the water cooler first, wait for the probe temperature to stabilize, and then turn on the laser
Shutdown sequence: Turn off the laser first, wait until the probe fully warms up, and then turn off the water cooling
Before each use, visually check the window for water mist and water droplets,Laser is strictly prohibited if dew condensation is discovered, wait until it is completely warmed and dried before testing
For the probe that has been dewed, stop water cooling and cooling, naturally warm up, and completely dry, check whether there is any watermark in the window, and optically clean if necessary
Regularly check the aging of the seal rings to avoid seal failure
Summary
The essence of dew condensation in most water-cooled thermoelectric power meters is:Cold surfaces encounter highly humid air and the temperature is below the dew point. Many on-site misunderstandings are to blindly reduce the temperature of the chiller, which instead amplifies the risk of dew condensation.
Technical support
If you need to further investigate the power meter dew condensation or measurement abnormalities, please contact the laser optoelectronic technical service team.
Wuxi Jibeam Optoelectronic Instrument Co., Ltd.
Focus on laser testing·Be as accurate as one
18516359331
frank-liu@lasbeam.cn
www.lasbeam.cn
