2022.03.18
Precision Control Technology of Vacuum in Micro-Displacement and Inclination Measurement of Michelson Laser Interferometer sensor
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Precision Control Technology of Vacuum in Micro-Displacement and Inclination Measurement of Michelson Laser Interferometer sensor
Abstract: In the precise micro-displacement and inclination measurement of Michelson laser interferometer sensor, it is necessary to accurately control the degree of vacuum; otherwise it will cause huge fluctuations due to factors such as deformation, refractive index and temperature, and even make the measurement impossible. This article introduces the automatic control technology of vacuum level using electronic flow control valve, and introduces the specific implementation scheme in detail.
1. Question
As a high-precision optical instrument, Michelson laser interferometer sensor has been widely used. It can be used to measure wave length, gas or liquid refractive index, thickness, displacement and inclination. It can measure length, velocity, angle, flatness, straightness and verticality of high-precision measurement, etc. However, in high-precision measurement, Michelson laser interferometer sensor will be seriously affected by atmosphere environment. For this reason, the measured object is generally placed in a low-pressure vacuum environment, as shown in Figure 1, and the degree of vacuum is precisely controlled with an electronic flow control valve, or it would cause the following problem:
(1) Gas refractive index fluctuations in the test environment will have a serious impact on high-precision measurements. If a special gas refractive index correction device is used, the measurement accuracy can only reach micron or sub-micron level, and higher-precision measurement cannot be reached.
(2) If there is a temperature change in vacuum chamber, the air pressure in chamber will also change drastically. The corresponding refractive index will also fluctuate severely, which will seriously affect the interferometer measurement.
(3) During the vacuuming process, the internal and external pressure difference will cause micro deformation of vacuum chamber, and at the same time, it will also cause the optical window to be displaced and tilted, thereby changing the optical path of the measurement optical path.
(4) In some test fields with variable temperature requirements, it is required that the measured object be heated as soon as possible and the temperature is homogeneous, which requires vacuum degree to be controlled at a certain level, such as about 100Pa, so as to keep the ability of convection and heat conduction.
To sum up, in the precise measurement of micro-displacement and inclination of Michelson laser interferometer sensor, it is necessary to accurately control the degree of vacuum. This article will introduce the automatic control technology of vacuum degree and the specific implementation scheme.
2. Implementation plan
During the test of Michelson laser interferometer sensor, vacuum degree is generally kept constant at about 100kPa and does not change with temperature. Because of this, vacuum degree control system as shown in Figure 2 is proposed to be implemented using an electronic flow control valve, and the specific conditions are as follows:
(1) Use the capacitance vacuum gauge with a range of 1 Torr for vacuum measurement, and its accuracy can reach ±0.2%.
(2) The high-precision PID vacuum pressure controller incorporating an electronic flow control valve with 24-bit A/D acquisition is used to match the measurement accuracy of high-precision vacuum pressure sensor and ensure the control accuracy.
(3) Install a stepper motor proportional valve at air inlet of vacuum chamber to precisely adjust air intake flow.
(4) During the control process, after vacuum pump turn on, it pumps at full speed and keeps the pumping speed unchanged. Then the PID parameters of controller are self-tuning, so that the controller can automatically adjust micro opening of KaoLu’s FC series electronic flow control valve to reach precise control of vacuum degree of the chamber.
For further information, please visit https://www.genndih.com/proportional-flow-control-valve/mid-flow-proportional-valve-0-130L-min.html
Abstract: In the precise micro-displacement and inclination measurement of Michelson laser interferometer sensor, it is necessary to accurately control the degree of vacuum; otherwise it will cause huge fluctuations due to factors such as deformation, refractive index and temperature, and even make the measurement impossible. This article introduces the automatic control technology of vacuum level using electronic flow control valve, and introduces the specific implementation scheme in detail.
1. Question
As a high-precision optical instrument, Michelson laser interferometer sensor has been widely used. It can be used to measure wave length, gas or liquid refractive index, thickness, displacement and inclination. It can measure length, velocity, angle, flatness, straightness and verticality of high-precision measurement, etc. However, in high-precision measurement, Michelson laser interferometer sensor will be seriously affected by atmosphere environment. For this reason, the measured object is generally placed in a low-pressure vacuum environment, as shown in Figure 1, and the degree of vacuum is precisely controlled with an electronic flow control valve, or it would cause the following problem:
(1) Gas refractive index fluctuations in the test environment will have a serious impact on high-precision measurements. If a special gas refractive index correction device is used, the measurement accuracy can only reach micron or sub-micron level, and higher-precision measurement cannot be reached.
(2) If there is a temperature change in vacuum chamber, the air pressure in chamber will also change drastically. The corresponding refractive index will also fluctuate severely, which will seriously affect the interferometer measurement.
(3) During the vacuuming process, the internal and external pressure difference will cause micro deformation of vacuum chamber, and at the same time, it will also cause the optical window to be displaced and tilted, thereby changing the optical path of the measurement optical path.
(4) In some test fields with variable temperature requirements, it is required that the measured object be heated as soon as possible and the temperature is homogeneous, which requires vacuum degree to be controlled at a certain level, such as about 100Pa, so as to keep the ability of convection and heat conduction.
To sum up, in the precise measurement of micro-displacement and inclination of Michelson laser interferometer sensor, it is necessary to accurately control the degree of vacuum. This article will introduce the automatic control technology of vacuum degree and the specific implementation scheme.
2. Implementation plan
During the test of Michelson laser interferometer sensor, vacuum degree is generally kept constant at about 100kPa and does not change with temperature. Because of this, vacuum degree control system as shown in Figure 2 is proposed to be implemented using an electronic flow control valve, and the specific conditions are as follows:
(1) Use the capacitance vacuum gauge with a range of 1 Torr for vacuum measurement, and its accuracy can reach ±0.2%.
(2) The high-precision PID vacuum pressure controller incorporating an electronic flow control valve with 24-bit A/D acquisition is used to match the measurement accuracy of high-precision vacuum pressure sensor and ensure the control accuracy.
(3) Install a stepper motor proportional valve at air inlet of vacuum chamber to precisely adjust air intake flow.
(4) During the control process, after vacuum pump turn on, it pumps at full speed and keeps the pumping speed unchanged. Then the PID parameters of controller are self-tuning, so that the controller can automatically adjust micro opening of KaoLu’s FC series electronic flow control valve to reach precise control of vacuum degree of the chamber.
For further information, please visit https://www.genndih.com/proportional-flow-control-valve/mid-flow-proportional-valve-0-130L-min.html