Automated Barometric Chamber for Entomology Experiments: the Precise Control Solution of Positive Pressure and Negative Pressure

1. Why environment would affect insects?


The environment in which various organisms live affects and changes their lifestyles. These environmental conditions mainly include factors such as wind, rain, soil composition, radiation, temperature, and atmospheric pressure. Numerous studies have shown that adverse weather conditions often associated with changes in air pressure, can affect reproduction, feeding and habitat. Other Factors are insect behaviors. Such as flight, spawning, parasitism, mating, and singing are affected by air pressure.

For the study of correlation between insect behavior patterns and air pressure, the currently commonly used method is to observe and record under natural conditions, which has problems such as low efficiency, long cycle and inaccuracy.

Some laboratories use manually controlled air pressure chambers, but there are problems such as inaccurate air pressure control, inability to accurately imitate the slow change process of natural pressure for a long time, and the controllable air pressure change range is very narrow. Recently, one of our customers hopes to automatically control the positive and negative pressures of air pressure chamber used for insect research. The specific requirements are as follows:
  1. Air pressure control range: Based on a standard atmospheric pressure, it can reach the precise control of air pressure in air pressure chamber within the positive and negative pressure range. That is, the absolute pressure in air pressure chamber can be precisely controlled within the range of 90kPa~110kPa.
  2. Air pressure control form: It can automatically simulate the slow changing process of natural atmospheric pressure which means that air pressure change can be controlled according to change direction and speed set arbitrarily. Air pressure can be accurately and constant at any set point. In a word, the entire air pressure change process can be precisely controlled according to broken line form set arbitrarily.
  3. Air pressure control accuracy: within the range of 90kPa~110kPa, the control accuracy at any pressure is less than ±0.1%.

In order to meet the above requirements put forward by customers, this article will propose a corresponding high-precision air pressure program control solution. The solution will adopt the method of dynamic balance of gas in and out of closed container, use high-pressure gas cylinders as high-pressure gas source, vacuum pump for pumping, and use the dual-channel vacuum pressure program controller to collect pressure sensors and simultaneously control the opening of inlet and outlet Proportional Pressure Regulator. In this way, it can reach accurate control and long-term stable operation of any set pressure change program.

2. How to solve the problem?


From the above requirements put forward by customer, it can be seen that pressure control of air chamber for study of insect behavior is a typical problem of automatic control of positive and negative pressure.
This automatic control of positive and negative pressure needs to solve the following problems:
  1. How positive pressure (pressure) and negative pressure (vacuum) are formed
  2. Positive and negative pressure automatic control methods and control instruments
  3. Selection of pressure sensor
  4. Selection of Proportional Pressure Regulator

In order to solve the above problems, the specific solution proposed in this article is shown in Figure 1.

First, the solution uses a dynamic balancing method to create positive and negative pressure in air chamber. As shown in Figure 1, a high-pressure gas source is arranged at air inlet end on left side of air pressure chamber. A vacuum pump is arranged at air outlet end on right side of air pressure chamber. If air intake flow is greater than the exhaust flow, a positive and negative pressure would be formed. Then, air intake and outlet flow is regulated by inlet and outlet valves.

The adjustment and control of positive and negative pressure of air chamber is a typical split-range control case. The output of one regulator is used to simultaneously drive several actuators with different working ranges. The regulator here is KaoLu's Proportional Pressure Regulator shown in Figure 1, and actuators with different working ranges are air intake valve and exhaust valve.

It can be seen that the Proportional Pressure Regulator is required to have a split-range control function. Proportional Pressure Regulator is required to have the function of simultaneously adjusting the opening of the intake valve and exhaust valve for different working ranges (positive pressure or negative pressure range)

In addition, in order to ensure control accuracy, the selected Proportional Pressure Regulator is an ultra-high-precision PID regulator, with 24-bit AD and 16-bit DA converters, and double-precision floating-point arithmetic functions, and minimum output percentage can reach 0.01%.

In order to ensure that pressure change in air pressure chamber reaches the control accuracy proposed by customer, it is also necessary to select a high-precision pressure sensor. If the control accuracy of ±0.1% is to be reached, the measurement accuracy of pressure sensor needs to reach ±0.05%. Similarly, the pressure control accuracy also depends on the adjustment accuracy and response speed of air intake and exhaust valves.

For air pressure chambers used in entomological experiments with smaller volumes, the valves are required to have an ultra-high response speed. Here, we use KaoLu's Proportional Pressure Regulator driven by a stepping motor. The full opening speed of Proportional Pressure Regulator is 0.8 seconds, with ultra-low vacuum leak rate and 7bar positive pressure resistance. A series of Proportional Pressure Regulator with different port diameters are available to meet automatic air pressure chambers of different specifications and sizes. The most important thing is that Proportional Pressure Regulator can be directly driven by an analog signal of 0~10V , 4~20mA or RS485, and it has high linearity, repeatability and fast speed.

After the above selection and configuration, according to solution shown in Figure 1, the configured Proportional Pressure Regulator is shown in Figure 2. Proportional Pressure Regulator shown in Figure 2 is an integrated instrument, and all components including the numerical Proportional Pressure Regulator, controller, power supply, etc. are integrated and installed in controller. There are push-in connectors on both sides of controller to connect air/air pump. There is a quick-plug connector for connecting air inlet/outlet of air pressure chamber on the back of controller. There are also special interfaces for connecting pressure sensor, computer communication and working power supply.

The pressure sensor is directly installed on side wall of air pressure chamber in an external form, which can detect the change of vacuum pressure in air pressure chamber more accurately. The signal and power leads from pressure sensor connect to the corresponding connectors on back of vacuum pressure controller. This form of external pressure sensor is more expandable, and different pressure sensors can be selected according to vacuum pressure control range of different air chambers or airtight containers, and it is easy to replace and install.

Computer communication adopts RS 485 interface with standard MODBUS protocol, so it can be connected to computer. Through the control software that comes with the PID controller, the computer can directly control PID regulator, and use the software interface to set up and run control program, and collect, store and display the whole process result curve of control process.

3. Conclusion


As a standard vacuum pressure control instrument, the above-mentioned positive and negative pressure precision control solution not only meets the requirements of automatic air pressure chambers for entomological experiments, but also has strong applicability and scalability, mainly reflected in the following several aspects:
  1. Vacuum pressure control in a wider range can be carried out, the absolute pressure control range can cover 0.1Pa~0.5MPa, and it has a very wide positive pressure and negative pressure control range.
  2. Various forms of control can be reached in the range of positive and negative pressure, such as separate control of positive pressure, separate control of negative pressure (vacuum degree), and continuous control of positive and negative pressure. All controls can be controlled by fixed points or by Automatic control of polyline programming programs.
  3. More functions can be expanded, such as air pressure control under different gases or mixed gases with different gas contents, and can also be used to control other environmental variables at the same time, such as temperature, humidity and light.

In short, the standardized vacuum pressure controller can meet pressure program control of various laboratory air chambers, and has a control accuracy of more than ±0.1%. At the same time, KaoLu's Proportional Pressure Regulator is also suitable for precise air pressure control of various vacuum pressure vessels (such as climate chambers, climate environment test chambers, vacuum atmosphere furnaces, vacuum drying ovens, rotary evaporators, precision low-temperature containers, freeze drying ovens and various spectrometers, etc.) It can greatly improve the degree of automation and control precision.

Do you want to know more about KaoLu's Proportional Pressure Regulator? Check our website for more details!