I. Preface
Recently, when handling customer feedback, our technical service team found that the problem of unstable readings of some water-cooled laser power meters originated from the use of power meters and lasers by users.Parallel waterway connection.
Although this connection method can save initial equipment costs and installation space, it will destroy the thermal balance conditions of the power meter, causing periodic fluctuations, drift and even jumps in the measurement data, which directly affects your production process control and R & D experimental accuracy.
As a professional manufacturer of laser power meters, we know that accurate and reliable power measurement is the basis for laser processing, scientific research experiments and equipment calibration. Based on the working principle of thermoelectric power meters, this paper will systematically analyze the technical problems of parallel waterways, and provide practical solutions.
2. The core working principle of pyroelectric laser power meter
The pyroelectric laser power meter adopts an indirect measurement method based on energy conversion, and its measurement accuracy completely depends on the stability of the system's heat flow:
Core technical requirements:
The heat dissipation capacity of the water-cooled heat sink must remain constant
The rate of change of inlet water temperature should be controlled within ±1℃/minute within
Cooling water flow must be stable without fluctuations
3. The root cause of unstable readings caused by parallel waterways
When the power meter and the laser share the same chiller and are connected in parallel, the following four technical problems arise:
3.1 Traffic distribution is uneven and dynamic
Parallel waterways follow "Water flows to places with little resistance" Hydrodynamic laws:
The internal waterway structure of the power meter probe is simple, and the water resistance is generally lower than that of the laser
Most of the cooling water flows preferentially to the power meter, resulting in insufficient cooling of the laser
When the laser output power changes, the internal water temperature rises and the water resistance changes dynamically
Flow is redistributed between the laser and the power meter, causing the power meter flow to fluctuate between large and small
impact: Flow fluctuations directly change the heat dissipation efficiency of the heat sink, causing the temperature difference of the power meter to change, which ultimately results in irregular jumps in the power reading.
3.2 Waterway pressure fluctuates violently with laser operating state
laser in "Standby → Light out → Standby" During the cycle, heat production changes:
standby state: The laser has almost no heat and the water pressure is stable
light-emitting state: A large amount of heat is generated instantly, the cooling water expands when heated, and the pressure in the waterway rises sharply
Stop the light: Heat production stops and water pressure drops rapidly
This periodic pressure fluctuation is transmitted directly to the power meter side through parallel piping. For thermoelectric power meters that are extremely sensitive to heat flow, corresponding measurement errors can be generated when flow changes.
3.3 Temperature cross-contamination and thermal reflux
In parallel waterways, return water from the laser and power meter mixes at the inlet of the chiller:
The large amount of heat generated by the laser significantly increases the return water temperature
After the high-temperature return water enters the chiller, the outlet water temperature increases overall
The response of the chiller temperature control system lags behind, and the power meter inlet water temperature fluctuates periodically.
The heat generated by the power meter will in turn affect the performance of the laser
What is more serious is that when the laser suddenly stops emitting light, low-temperature water on the power meter side may flow back to the laser side through parallel pipes. This kind of thermal reflux will cause the temperature of the power meter probe to change violently in a short period of time, causing large power fluctuations and measurement errors.
3.4 Bubble accumulation and cavitation problems
Bubbles are easy to accumulate at branch points and elbows of parallel waterways:
Bubbles hinder the flow of cooling water, resulting in poor local heat dissipation
When pressure fluctuates, the bubble bursts, creating a small pressure shock
Bubbles adhere to the surface of the power meter heat sink, forming an insulation layer
The bubble problem is particularly prominent in high-power laser systems, which can cause random peaks or troughs in power readings, which greatly affects data repeatability.
4. Recommended solution: Configure a separate water cooler
strongly recommended: Configure the power meter with a separate water cooler-this is the simplest and most effective solution.
4.1 Three core advantages of a separate water cooler
4.2 Comparison of individual water cooler vs parallel waterway
5. Key specifications for installation and use of water cooling systems
5.1 Cooling water parameter requirements
5.2 System installation points
Install a filter element at the water outlet of the chiller to prevent impurities from entering the power meter probe
The inner diameter of the pipeline shall not be less than the power meter interface size
Minimize piping elbows and lengths
After the system installation is completed, water and exhaust for 1-2 minutes to ensure no bubbles
5.3 periodic maintenance requirements
Check the cooling water flow and temperature before each use
Replace cooling water every 3-6 months
Clean chiller tanks and pipes once a year
Avoid the power meter being blown directly from the air conditioner outlet or direct sunlight
6. Suggestions for selection of water cooling machines
Q1: How to select a separate water cooler?
A1: The water cooler must meet two conditions at the same time:
Water flow meets power meter requirements
The cooling capacity is consistent with the range of the power meter, and the recommended cooling capacity is recommended.Greater than 20% of power meter range
*Example: The power meter is 10K-D48CP (range: 10kW). It is recommended to choose a water cooler with a cooling capacity of 12kW and above.*
Q2: Existing water coolers have enough flow but insufficient cooling capacity. How to solve the problem?
A2: It can measure the corresponding low-power laser. It is not recommended to use it for full-load measurement for a long time.
Q3: Parallel waterways have been used. Are there any temporary improvement methods?
A3: You can install a stop valve on the inlet and outlet water pipes of the power meter to manually adjust the fixed flow. But this is a stopgap measure,It is still recommended to switch to a separate water cooler connection as soon as possible.
Q4: What other factors can cause fluctuations in power readings?
A4: Other possible factors include:
There is dust or damage on the probe surface
Environmental temperature changes too much
unstable power supply voltage
Signal cable suffers from electromagnetic interference
Laser machining head damage
7. Technical support and contact information
If you encounter any problems during the use of the laser power meter, please feel free to contact the laser optoelectronic technical service team:
technical support hotline：18516359331
technical support email:frank-liu@lasbeam.cn
official website:www.lasbeam.cn
Thank you for your trust and support for Lasbeam Instruments Co., Ltd.!
