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The Challenge:
Implementing an effective system to control Vacuum Systems and monitor Parameters like pressure and Temperature of Micro Thrusters in vacuum.
The Solution:
Developing a computer-based system for the Micro Thruster test facility combining the Distributed features of Field-Point and the High Speed features of the Data Acquisition Card and SCXI signal conditioning. This system is accessible on any PC in the network.
Application
The micro-thruster used in satellites are subjected to different tests such as Environmental, Electrical and Pressure leak tests under different stages of development, qualification and acceptance. The system needs to control Root Blowers, Root Pumps, Electro-pneumatic valves, Air Compressor, Water Pump Pressurization and De-Pressurization Valves of the vacuum system in different sequences. The vacuum system is located over 60 meters away from the Control Room as per safety requirements. The system also needs to monitor chamber pressure, Injection Pressure, Tank Pressure, Filtered chamber Pressure, thrust, Chamber Temperature, Injection Temperature, Vacuum level, Valve Current and Flow rate. The system is provided with a safety shutdown in case of any abnormal condition. The system generates reports in the specified format.
Actual System
Space Craft Engines are widely used in orbit to change the position of Satellites for Altitude and orbit corrections. Before integrating the thruster into a Satellite it undergoes many tests. Thrusters are fired in two modes Pulse Mode Firing (PMF) and Steady State Firing (SSF). Commands are generated for the flow control valve with ON/OFF time and no of pulses in PMF mode and Duration in seconds in SSF mode. Depending on the performance the Thruster is subjected to many tests in different stages.
In the earlier Manual system, for each test one person is required to switch on the Electro pneumatic valves, Root Blower pumps, Rotary Pumps etc, one more person was required to start the test communicating through a walkie-talkie as the Micro Thruster Test Facility is about 60m from the Control Room. It also required the operator to monitor for any abnormal condition and to shutdown the system manually. Logging the data was also initiated and stopped manually thereby acquiring a lot of unwanted data.
In the LabVIEW based system, all this is fully automated. From the control room, the user can start the test and control the Electro pneumatic valves, Root Blower pumps, Rotary pumps etc., and in any abnormal condition the system is provided with safety shutdown. Any PC on the network can monitor the parameters while the test is going on.
Hardware:
The Test facility is located 60 meters away from the Control Room. So the system uses FP-1600 Ethernet Network Modules for control and status check of all Digital I/O. This removes the need to have large amount of 230V AC wiring between the Test facility and control room. Four Root Blower pumps and Four Rotary pumps are connected to one FP-RLY-420, All 16 Electro pneumatic valves connected to two
FP-RLY-420 Modules, Water Pump, Air compressor, Pressurization and De-Pressurization Valve to the fourth FP-RLY-420 Module. The status of all the above valves and motors are fed back through four
FP-DI-330 modules controlled by another FP-1600 module.
The Analog signals to be monitored are taken by shielded cables to the SCXI system housed in the control room, which contains two SCXI-1125 Analog input Modules on an SCXI-1000 Chassis, SCXI-1320 Terminal blocks are used to connect the signals. The SCXI Chassis is connected to a 16-bit DAQ card
PCI-6034E. The counter signals are routed through the SCXI-1180 feed through panel.
Software Implementation:
Software for the test system is divided into several functional areas as Configuration Editor, Run Editor, Data Acquisition, and Offline Analysis. Configuration Editor where the monitoring parameters need to be selected and Properties for each parameter such as Gain, Sensitivity and Offset can be set. These properties are used to convert acquired voltage from SCXI to their respective Engineering units. The voltage acquired is converted to Bar for chamber Pressure, Injection Pressure, Tank Pressure, Filtered chamber Pressure, Deg C for five Temperature Channels, Grams for Thrust, mAmp for Valve Current, mBar for Vacuum level for Chamber and pump and Newton for Flow Rate. Options are also available for opening an existing configuration file/save the current configuration parameters and to quit the configuration editor.
Run Editor where Engine No, FlowcontrolValve No, Run No, Project Name, Mode of Testing, Mode of Firing can be entered. Depending on mode of firing, PMF-On time, Off Time, No of Pulses to be entered. SSF - Duration in seconds to be entered
One of the interesting screens is the Data Acquisition screen. The System can control 16 Electro pneumatic Valves, four Root Blowers, four Root Pumps, Water Pump, Air compressor, Pressurization and De-Pressurization Valve. The Selected Channels can be viewed on the graph. Three Pressure channels acquisition can be viewed on one graph and two Temperature channels acquisition can be viewed on another.
The Acquisition starts by giving Flow Control Valve Command as PMF/SSF. Counters are used to generate Pulses and the Acquisition is based on a TTL Digital Trigger. Whenever trigger occurs, acquisition will start and depending on the mode of firing, whether it is PMF, after predefined number of pulses the acquisition stops. In case of SSF, after the duration in seconds elapses the acquisition stops.
The system stores the acquired data in Binary Format. Offline analysis for any test, depending on the mode of firing, is done by extracting the data for the selected pulse/time interval. The Impulse bit, thrust, Centroid time, flow rate and total flow with given formula are calculated. Reports are generated and Provision to take printouts of that particular instant/pulse.
The System can be monitored from any PC on the network while the test is going on.
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