Customer SolutionsUsing NI LabVIEW, Compact FieldPoint, and PXI for Precise Control and Monitoring of Vacuum Chambers
Author(s):Mondeep Duarah, Captronic Systems Pvt. Ltd.; Anu Kalidas, Captronic Systems Pvt. Ltd.
Industry:Industrial Controls/ Devices/ Systems
Product:Compact FieldPoint, FieldPoint, LabVIEW, PXI/CompactPCI
The Challenge:Implementing a reliable and rugged automatic control system for a vacuum chamber, which continuously operates 24 hours a day for several days.
The Solution:Developing the automatic control system for the vacuum chamber using National Instruments Compact FieldPoint and PXI Windows.
Vacuum Chamber Test System Requirements A leading manufacturer of vacuum chambers required a solution for controlling and monitoring of vacuum chambers. Components kept inside the vacuum chamber were subjected to different tests such as environmental, electrical, and pressure leak tests under different stages of development, qualification, and acceptance. The system needed to control rotary pumps, root pumps, electro-pneumatic valves, air compressor, water pump pressurization, and depressurization valves of the vacuum system and diffusion pumps in different sequences. The vacuum system is located away from the control room per safety requirements. The system also needed to monitor parameters returned by the active gauge controller and turbo instrument controller. The system required safety interlocks and shutdown information in case of any abnormal condition. The chamber needed to continuously run for several days with out stopping. We decided to use an NI PXI, Windows, and Compact FieldPoint real-time-based test system, which introduced reliability and flexibility in sequential operation of various subsystems. The system took care of all of the interlocks, which reduced human intervention during operation of the chamber. Necessary actions automatically initiate if any anomaly during operation of the chamber is detected by FieldPoint. The system records test data and generates reports from the logged data. General Description of Control Actions There are basically three types of pumps – root pumps, rotary pumps, and diffusion pumps. Rotary pumps are used for backing of diffusion pumps and root pumps for pre-evacuation of the high vacuum chamber. Root pumps can evacuate the chamber to around 0.001 m bars. Diffusion pumps are used to create high vacuum inside the chamber after the root pumps performs pre-evacuation. Users can only operate diffusion pumps after backing pressure and working temperature (as set by the user) is achieved. There are two diffusion pumps and four rotary pumps. Two of the rotary pumps are used for backing the diffusion pumps and two are used for pre-evacuation. A series of valves connects the rotary, diffusion, and chamber lines. There is flexibility in the system so that if one of the pumps fails, another pump can perform the functionality of that pump by suitably selecting the valves to be opened. Under normal working conditions, rotary pumps are turned on first to ensure that the diffusion pumps have reached the set backing pressure. After the set pressure is achieved, heaters are turned on until the set working temperature is achieved. Once the working temperature is attained, the diffusion pump are turned on and the high vacuum valves are opened provided the chamber has been pre-evacuated to the set pre-evacuation pressure also known as roughing pressure. In short, diffusion pumps are started only if backing pressure, roughing pressure, and working temperature is attained. System Configurations We designed the system to accept digital inputs from the control console or accept feedback from the vacuum chamber subsystem. Control logic and checks are implemented and performed on the Compact FieldPoint system. The software running on the PXI-8186 RT controller is the human machine interface (HMI) between the NI-based system and the control hardware, which involves valves and pumps. The user has the option to either use the controls provided in the software or the actual knobs and switches on the chamber control panel. The local/remote switch on the control console panel, which sends a digital input to the cFP-DI-301 digital input module determines whether to use the controls on the panel or on the software. All the control routines running on Compact FieldPoint are activated when a digital input from switches on the control console is received. There are three modes of operation: manual, auto, and standby. In manual mode, the user selects the sequence of operation and only the control and display are performed through the FieldPoint real-time software. Based on the local/remote switch selection, the sequences can be selected either through front panel knobs or through the knobs provided in the software. In auto mode, the FieldPoint real-time software executes the control sequences in a pre-defined manner. The pumps and valves that are used in case of auto mode are fixed. Once in standby mode, the backing rotary pumps and valves are turned on until backing pressure set point is attained. Once the set point is reached, the heaters are turned on until the working temperature of the diffusion pump is reached. The entire control logic routine is resident on the Compact FieldPoint module. These routines are invoked depending on the mode in which the vacuum system is operated. The PXI controller acts as the host system for the Compact FieldPoint module. The PXI controllers are used for data logging and viewing data published from the cFP-2010 real-time controller/interface. We use two PXI controllers keeping the redundancy factor in view. At a time the cFP-2010 real-time controller/interface can receive information from one controller and the second controller takes over only if the first controller fails. Data logging continues in both the controllers. One of the key features of the system is that during power failures, the system automatically switches to a standby power source. In this state, a set of pumps and valves are turned off and the system automatically restarts when the power is restored without human intervention. We used an M Series module (PXI-6220 multifunction DAQ) for data acquisition from the test specimen placed inside the chamber. System Software After logging on to the system, the user enters the run number and other test identification parameters. The host system provides a mimic display screen for monitoring state of pumps, valves, and animated evacuating pipes. During the test, the host gets continuous feedback from the FP-TC-120 thermocouple input system of all the parameters. These values are displayed on the host system along with the set values. Some of the key features of the software are:
Success with Compact FieldPoint and LabVIEW With the cFP-2010 real-time controller/interface platform we created an extremely reliable, rugged, and highly precise control system by replacing a PLC and commercial SCADA package with Compact FieldPoint and LabVIEW. Thus, we integrated the control system and data acquisition system to one platform rather than having a separate control system and separate high speed data acquisition system. For more information, contact: Mondeep Duarah Senior Manager – Design and Development Captronic Systems Pvt. Ltd. I Block Koramangala Bangalore-560034 Karnataka Tel: +91-80-2 553 5046 Fax: +91-80-2 550 4054 E-mail: mondeep@captronicsystems.com |
