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Digital Needle Valve in vacuum gauge calibration device
Integrating a digital needle valve in a portable vacuum gauge calibration device in order to reach the field calibration of vacuum gauge, based on static comparison method calibration technology. This article focuses on a technical scheme using a miniature digital needle valve and an upstream and downstream two-way gas flow control mode, combined with dual-channel high precision. The use of digital needle valve with a vacuum PID controller can solve the problem of field calibration and portability under the premise of precise vacuum control.
1. Question
As a vacuum sensors or vacuum gauges are widely used in many fields and require regular calibration, the calibration device of vacuum gauge is a complete measurement system including a vacuum standard, a vacuum pump, a vacuum valve and a connecting pipeline. Its size is generally large and inconvenient to move, and is mostly fixed in the laboratory. Most existing vacuum gauge calibration methods are to remove the vacuum gauge used on field inspection. To meet the needs of field calibration, the following issues need to be addressed:
(1) Reduce the size of related components, making the vacuum gauge calibration device easy to carry.
(2) Adopt numerical control and digital needle valve to improve the precision of gas flow regulation.
(3) Improve the vacuum degree control method and vacuum degree control accuracy and stability.
In order to reach the field calibration of vacuum gauge and portability of calibration device, based on the static comparison method calibration technology, this article will focus on a technical scheme using a miniature digital needle valve and an upstream and downstream two-way gas flow control mode, combined with a high-precision vacuum PID controller. It can solve the problem of field calibration and portability under the premise of precise control of vacuum degree, and the fluctuation of vacuum degree can be controlled within ±1%.
2. Portable vacuum gauge calibration device technical scheme
The entire structure of portable vacuum gauge calibration device is shown in Figure 1, which is a schematic diagram of a typical structure of the calibration device in the vacuum range of 0.1~760 Torr. The details of the plan are as follows:
(1) Using the method of comparative static analysis, the calibrated vacuum gauge is compared with the reference standard vacuum gauge. The reference standard vacuum gauge uses two capacitive film vacuum gauges to cover the entire vacuum calibration range, refer to the standard vacuum gauge also acts as a vacuum control sensor.
(2) The vacuum degree controller adopts a two-channel high-precision vacuum degree controller. The A/D of controller is 24 bits, and the D/A is 16 bits, which can correspond to high-precision signal output of capacitive film vacuum gauge and meet the vacuum degree control accuracy requirements. The two channels of controller correspond to the input signals of two vacuum gauges and the precise adjustment of air intake and exhaust flow of two-way digital needle valve. In the process of vacuum degree control, the two-way sensor signals can be automatically switched as required to reach programmable automatic control within the full range. The controller has PID self-tuning function and standard MODBUS communication protocol.
(3) Two digital needle valves are used to adjust the air intake and exhaust flow respectively, and the controller adopts a bidirectional mode to adjust the two needle valves respectively. The air intake needle valve is mainly adjusted in the rough vacuum range, and the air intake needle valve is mainly adjusted in the high vacuum range. When the vacuum degree is constant in the full range, the vacuum degree fluctuation rate can be controlled within ±1%. Further information on the digital needle valve, please visit:
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