The Challenge:

Implementing a reliable and rugged automatic control system for a vacuum chamber, which operates continuously for 24hours a day, spanning over several days. This also involved interfacing a data acquisition and monitoring system for the test specimen placed inside the chamber.

The Solution:

The automatic control system for vacuum chamber was developed on PXI-Windows and FieldPoint RT. The system made use of cFP-2010 as a logic controller for the vacuum chamber control and the NI 8186 Controller and PXI-6220 as the host for FieldPoint-RT system and data acquisition respectively. Different control settings are configured on the host PC and downloaded to the FieldPoint-RT system, which runs and controls the vaccum chamber. The user interface is provided on a Host PC.

Introduction:

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 De-Pressurization Valves of the vacuum system and Diffusion Pumps in different sequences. The vacuum system is located away from the Control Room as per safety requirements

The system also needed to monitor parameter returned by the Active Gauge Controller and Turbo Instrument Controller. The system was to be provided with safety interlocks and shutdown information in case of any abnormal condition. The chamber was to run continuously for several days with out stopping.

We decided to go with a PXI-Windows and Field Point-RT based test system which introduced reliability and flexibility in sequential operation of various subsystems. It reduced the human intervention during operation of the chamber as all the interlocks were take care of. Necessary actions are initiated automatically if any anomaly during operation of the chamber is detected by cFP. Test data is recorded and report is generated from the logged data.

A 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. Also diffusion pumps can be operated only 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 will be 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, the functionality of that pump can be done by another 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 will be turned on and the high vacuum valves will be opened provided the chamber has been pre evacuated to the set pre evacuation pressure also known as roughing pressure. In short, diffusion pumps will be started only if backing pressure, roughing pressure and working temperature is attained.

System Configurations:

The system is designed 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 controller is the HMI between the NI based system and the control hardware, which involves valves, pumps etc. The user has an 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 module decides whether to use the controls on the panel or on the software. All the control routines running on cFP are activated when a digital input from switches on the control console is received.

There are three modes of operation:

• Manual Mode
• Auto mode
• Standby mode

In the manual mode the user selects the sequence of operation and only the control and display are be performed through the FieldPoint-RT 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-RT software executes the control sequences in a pre-defined manner. Also the pumps and valves that are used in case of auto mode are fixed.

Once in standby mode, the backing rotary pumps and valves will be turned on until backing pressure set point is attained. Once the set point is reached, the heaters are turned on till the working temperature of the diffusion pump is reached.

The entire control logic routine is resident on the FieldPoint-RT. 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 cFP. The PXI controllers are used for data logging and viewing, published from the cFP controller. Two PXI controllers are used keeping in view the redundancy factor. At a time the cFP controller 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 cuts the systems switches to a standby power source automatically. In this state a set of pumps and valves are turned off and the system restarts automatically when the power is restored without human intervention.

M-Series DAQ board PXI-6220 is used for data acquisition from the test specimen placed inside the chamber.

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 will be getting continuous feed back from the FP-RT system of all the parameters, these values will be displayed on the host system along with the set values. Some of the key features of the software are:

• Usage Profiles-Operator and Administrative level.
• Configuration-provision for entering test name, run number, sampling rate, channel configuration, configuration of pressure measuring device AGC and TIC.
• Acquire and log data to citadel database keeping redundancy into consideration.
• System error management and handling.
• Mimic display of active pumps, valves and animated pipes.
• Historical data viewing and real time trending using Labview DSC.
• Implementation of safety interlocks
• Soft panel for AGC and TIC.
• Control routine for cFP-RT.
• Event logging and management.
• Customized report generation

Conclusion:

With the cFP-RT platform we were able to put up an extremely reliable, rugged and highly precise control system, all these were achieved by replacing a PLC and commercial SCADA package with cFP and LabVIEW. Thus we were able to integrate the control system and Data Acquisition system to one platform rather than having a separate control system and separate high speed Data Acquisition system.