Precision Control Technology of Pressure in Echelle Spectrometer and Its Implementation

Precision Control Technology of Pressure in Echelle Spectrometer and Its Implementation Precision Control Technology of Pressure in Echelle Spectrometer and Its Implementation

Abstract: In order to reach the high-precision measurement of Echelle spectrometer, it is necessary to conduct precise and constant control of temperature and pressure for a long period in the whole process. This article will introduce the automatic pressure control technology for precise control of pressure in Echelle spectrometer using FC series high flow proportional valve, and introduce the specific implementation scheme in detail, especially the bi-directional control mode with better control effect.

1. Question
As a full-spectrum direct-reading spectrometer, Echelle spectrometer is widely used in astronomy, geology, mining, chemical industry, metallurgy, medicine, environmental protection, agriculture, food hygiene, biochemistry, commodity inspection and national defense. Due to the serious influence of temperature and pressure, the Echelle spectrometer generally requires precise control of working temperature and pressure, especially the pressure control requires very high precision which using FC series high flow proportional valve (https://www.genndih.com/proportional-flow-control-valve.htm). If the control precision is not enough, it will bring the following effects:
(1) The pressure fluctuation will change the refractive index of gas in Echelle spectrometer.
(2) The pressure fluctuation will also cause the difference in pressure inside and outside the spectrometer to cause slight deformation of the optical path of spectrometer (especially at the optical window). At the same time, changes in temperature will also directly cause changes in air pressure. In conclusion, in order to reach the high-precision measurement of Echelle spectrometer, it is necessary to imply precise and constant control of temperature and pressure for a long period in the whole process. This article will introduce the automatic control technology of pressure for precise control of pressure in Echelle grating spectrometer using FC series high flow proportional valve, and introduce the specific implementation scheme in detail.

2. Implementation plan
The structure of pressure control system of Echelle spectrometer is shown in the figure. In the specific implementation process, it is necessary to notice the following aspects according to the specific situation:
(1) The working pressure of Echelle spectrometer is generally around an atmosphere pressure of 760torr, so it is necessary to select a pressure sensor that can meet the design requirements with measurement accuracy under this pressure. Choosing KaoLu’s high flow proportional valve is the best decision.

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(2) The automatic pressure control adopts a 24-bit high-precision PID controller. If the 24-bit measurement accuracy still cannot match the accuracy of pressure sensor, a higher-precision controller is required which is KaoLu’s high flow proportional valve.
(3) The pressure control adopts bi-directional mode, that is, the air intake and exhaust flow are adjusted at the same time, but for pressure control near an atmosphere pressure, generally, air intake flow is fixed and exhaust flow is automatically adjusted to reach constant pressure control.
(4) According to the working chamber size of Echelle spectrometer’s different sizes, different outlet flow control valves need to be selected. For large-sized space working laboratory, the outlet flow control can choose a high flow proportional valve with a larger outlet diameter; while for a small-sized space studio, the outlet flow control needs to choose a smaller and more precise high flow proportional valve. The same goes for the vacuum pump used for vacuum suction.