232022.03
Rotary Evaporators: Integrated Controllers for Vacuum, Temperature and Rotation with Corrosion Resistant Digital Control Valves
Rotary Evaporators: Integrated Controllers for Vacuum, Temperature and Rotation with Corrosion Resistant Digital Control Valves
Abstract: At present, rotary evaporators can be built in different ways in various laboratories. In terms of vacuum control of evaporators, local customers generally require that they can replace the more expensive foreign vacuum control systems, improve the programming and automation level of vacuum control, improve the accuracy and stability of vacuum control, and solve the corrosion resistance of control valves. The problem even requires the use of controller to program temperature, vacuum and rotation at the same time. According to the improvement requirements put forward by users, this article focuses on corresponding solutions, and introduces related products such as high flow proportional valve especially used for evaporator temperature, vacuum degree and rotary motor control.

1. Users’ requirement
A rotary evaporator is the common equipment in laboratory. Through the electronic control in evaporator, the solvent in flask is rapidly evaporated under the appropriate rotation speed, temperature and vacuum degree. The working vacuum range of general rotary evaporator is 1 to 760 mmHg (absolute vacuum). In specific applications, the vacuum level will be set and controlled according to the requirements of different mixtures. As simple common laboratory equipment, the rotary evaporator can be built by each one in laboratory, and there are also various specifications for ordering in market. For the rotary evaporators currently used in some user laboratories, users put forward clear requirements in the following aspects:
(1) Some laboratories are equipped with imported rotary evaporators, but they also need to be equipped with higher-priced vacuum controllers separately, hoping to replace them with local products.
(2) Local and self-built rotary evaporators are expected to be equipped with multi-functional and high-precision vacuum controllers to reach the programming and automation of computer control of test process. It is hoped that multiple sets of control process setting curves can be stored for direct recall. The computer sets the test program and displays the changes of entire control process.
(3) At present, the vacuum control process of international and local rotary evaporators generally adopts the valve on-off or vacuum pump start-stop method. The control accuracy and stability are weak. It is hoped to use a high-speed digital proportional valve with continuously adjustable opening. (4) In recent years, high flow proportional valves in vacuum control devices of international and local rotary evaporators generally lack corrosion resistance, and it is hoped to use vacuum regulating valves that are resistant to corrosive gases and liquids.
(5) For some self-built rotary evaporators, it is hoped that temperature control, vacuum control and rotation control can be integrated to reduce the complexity of instrument and its operation, and to improve the level of integration and automation.
This article focuses on corresponding solutions for the above requirements, and introduces the integrated temperature, vacuum and rotation controller specially used for evaporators and the corrosion-resistant needle valve driven by stepper motor, which can meet the needs of different users of rotary evaporators’ test requirements.

2. Local 24-bit high-precision multi-functional controller
In order to reach the test and program control of temperature, vacuum degree and rotation of rotary evaporator, KaoLu have developed the VPC series 24-bit high-precision programmable PID general controller, as shown in Figure 1. This series of PID controllers are very extraordinary and cost-effective.



The main performance indicators of VPC series controllers are as follows:
(1) Precision: 24-bit A/D, 16-bit D/A.
(2) Maximum sampling speed: 50ms.
(3) Various input parameters: 47 input signals (thermocouple, thermal resistance, DC voltage) can be connected to various temperature and vacuum sensors for measurement, display and control.
(4) Various output forms: 16BIT analog signal, 2A (250V AC) relay, 22V/20mA solid state relay, 3A/250VAC SCR.
(5) Multi-channel: independent 1-channel or 2-channel output. 2 channels can reach simultaneous measurement and control of temperature and vacuum degree, and the alarm output channel can be used to control the start-stop of rotating motor.
(6) Multi-function: forward, reverse, forward and reverse bi-directional control, heating/cooling control.
(7) PID program control: The improved PID algorithm supports PV differential and differential advance control. It can store 20 groups of PID and support 20 program curves (50 segments each).
(8) Communication: Two-wire RS485, standard MODBUS RTU communication protocol.
(9) Display mode: digital hall and IPS TFT true color LCD.
(10) Software: The operation of controller and the data acquisition and storage can be reached through the software computer.
(11) Dimensions: 96×96×87mm (hole size 92×92mm).

3. Stepper motor drives corrosion-resistant high-speed needle valve
In order to reach high-precision adjustment in the process of vacuum degree control, KaoLu have developed a series of high flow proportional valves with different flow rates based on the electronic needle valve using stepper motors, as shown in Figure 2. The magnetic hysteresis of this series is much smaller than solenoid valves, and has a high-speed response within 1 second. In particular, the use of FKM sealing technology enables the high flow proportional valve to have superior corrosion resistance feature. The detailed technical indicators are shown in Figure 3 shown.



Model FC-20 FC-120 FC-300 FC-1000
Valve type Needle Valve
Spool Drift Diameter 0.9mm 2.25mm 2.75mm 4.10mm
Actuator Bipolar stepper motor control
Response time 0.8sec(Open to close)
Standard size G1/8” G3/8”
Fluid Inert gas and liquid
Contact Materials Stainless Steel
Pressure Range -1 ~ 7bar -1 ~ 5bar
Maximum Flow 50L/min @7bar 240L/min @7bar 290L/min @7bar 600L/min @7bar

 

Linearity ±2% ±0.1 ~ 1% ±0.2 ~ 5% ±11%
Repeatability
(Full scale)
±0.1%
Flow Resolution (Step length) 0.1L/min 0.1 ~ 0.2L/min 0.2 ~ 0.75L/min 1L/min
Shift Resolution (Step length) 12.7um 25.4um
Operating Temperature Range 0 ~ 84ºc
Seal Standard FKM or other choices of seals
Control Signal DC: 0 ~ 10V (or 4 ~ 20mA)
Power Supply DC: 24V (12W)

(Figure 3 Technical indicators of KaoLu’s FC high flow proportional valve)

FC series high flow proportional valve is equipped with a stepper motor drive circuit module, which provides the required power supply and control signal for FC high flow proportional valve, and converts the DC signal into step control of bipolar stepper motor, and can also provide RS485 direct control of serial communication. Its specifications and dimensions are shown in Figure 4.

For further information, please visit https://www.genndih.com/proportional-flow-control-valve/mid-flow-proportional-valve-0-130L-min.html

When rotary evaporator uses a numerically controlled high flow proportional valve, the high flow proportional valve can be installed at the front end of vacuum pump by an open-loop control method, and vacuum degree can be controlled by adjusting the pumping flow rate. However, the stability of this open-loop control method is poor, and it is difficult to reach higher purity requirements. In order to solve this problem, a closed-loop control method can be adopted, that is, an air intake control valve is added to the evaporator, and the precise control of vacuum degree can be reached by adjusting the air intake flow and the exhaust flow.