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Control and data acquisition system for multi-barrel pellet injector
Fusion Engineering and Design 66 /68 (2003) 893 /897 www.elsevier.com/locate/fusengdes
Control and data acquisition system for multi-barrel pellet injector S. Shibaev *, K.B. Axon EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, UK
Abstract A control and data acquisition system has been developed for the Mega-Amp Spherical Tokamak (MAST) multibarrel pellet injector to allow reliable operation with multiple pellet sizes. The system operates with one PC running Windows NT with four embedded PCI cards. All measurements and control functions are implemented on a PC. The system software consists of two programs. The first program provides pellet firing and registration of up to four fast signals associated with each pellet /pellet speed, mass, and other signals. The second program controls pellet preparation and all the pellet injector equipment. This program is realised as state machine */allowing a sequence of any number of states, it includes independent digital PID control of the temperature of each barrel. Both programs run conjointly using message exchange. The system is integrated and synchronised with the MAST control and data acquisition systems. # 2003 S. Shibaev. Published by Elsevier B.V. All rights reserved. Keywords: MAST; Pellet injector; Data acquisition; Digital control
1. Introduction The MAST [1] eight barrels pneumatic pellet injector was built at Risø [2] for use on the RTP tokamak. It was transferred to MAST and the barrels are enlarged at Risø to suit the higher fuelling rate needed for MAST. It prepares pellets in situ in eight barrels simultaneously. The modified injector has two small barrels */1.1 mm in diameter, two large */1.7 mm, and four medium */ 1.35 mm. The injector control and measurement system was originally made using a PLC and a * Corresponding author. Tel.: /44-1235-466-657; fax: /441235-466-379. E-mail address: [email protected] (S. Shibaev).
G64 computer; the pellet preparation was controlled by two analogue temperature controllers with common settings for four barrels. This paper describes an improved system to match the new barrel configuration and to incorporate the injector into MAST operations. The new system for pellet injector control and data acquisition has been made in three phases. The first task in adapting the pellet injector for MAST operation was to provide for pellet firing and recording pellet parameters. This was implemented prior to first use of the pellet injector on MAST. During first experiment a limitation of the original control system became obvious */there was no recording of pellet preparation temperatures; changes in configuration were very difficult
0920-3796/03/$ - see front matter # 2003 S. Shibaev. Published by Elsevier B.V. All rights reserved. doi:10.1016/S0920-3796(03)00372-7
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S. Shibaev, K.B. Axon / Fusion Engineering and Design 66 /68 (2003) 893 /897
(needing PLC re-programming). The second phase included replacement of the PLC and the G64 computer by a PC with two embedded cards */ analogue input and digital I/O */to allow flexible control and recording pellet preparation parameters. Finally, the temperature recording showed an imperfection of the original analogue temperature controller with the new barrels */it was not stable for all barrels and unable to control the temperature with sufficient precision and reproducibility. Besides, common settings for four barrels proved unsatisfactory. The third phase therefore included replacement of the original temperature controller by a 16 channels digital controller to control centre and outer temperatures of eight barrels. The centre controller adjusts the temperature of pellet preparation, whereas the outer controller provides the necessary temperature gradient. The essential improvement in the new system is the collection of all signals and control functions in one PC, which makes easy any changes in configuration. The system includes simple interface modules */linear amplifiers for analogue output and level converters for digital output. In view of possible extensions, the system is made in very general way fully using resources of embedded cards. Most of the user interface is completely general, only few parts (the mimics, for example) are specific for the pellet injector. The system hardware-PC with embedded cards, is selected, as most cost effective. The Windows NT platform provides faster program development with a convenient user interface.
Fig. 1. The scheme of data acquisition and pellet firing.
long gate pulse and short pulses for pellet firing as the digital output. To determine an accuracy of this system the delay between the trigger pulse and the output pulse is measured. Fig. 2 shows the additional delay of the first pulse in microseconds plotted as a function of fixed delay in ms. All measurements were made on the PC used for operations */an industrial PC with Athlon 750 MHz processor. The error bars show standard deviation of 20 samples in each point. The standard deviation of delay between two output pulses is less than 3 ms in the whole range of delays tested from 3 ms to 1 s. The whole error of pellet firing consists of a constant /180 ms shift of output pulse sequence and a random error of less than 10 ms. This shift is a sum of the interrupt and digital output propaga-
2. Pellet firing and data acquisition This part of the system is realised using a PCI ADC card. The card includes four channels 20 MHz ADC and 24 digital I/O channels. The control program logic is shown in Fig. 1. The MAST trigger starts acquisition, which continues to cover all data windows associated with pellet firing. The card generates an interrupt when the on-board data buffer is full. A timing thread acquires this interrupt. The thread generates a
Fig. 2. Additional delay of the first output pulse as a function of fixed delay.
S. Shibaev, K.B. Axon / Fusion Engineering and Design 66 /68 (2003) 893 /897
tion times. The random error is caused by the computer processes and system clock granularity. This result shows that the PC running Windows NT can control real time processes with accuracy of the order of 10 ms, keeping in mind that there is a delay of the order of 100 ms from the input to the computer process, and from the process and the output. The control program writes data from the four analogue channels into a data file and transfers this file to the MAST archive. This file contains also an item with pellet firing times. The program processes data before writing; it extracts fixed data windows associated with pellet firing times. There are two special settings for pellet data processing. If a channel is marked as ‘speed’, the whole range of data between two pellets is scanned for two pulses from light barriers. The delay between these pulses gives the pellet speed. If a channel is marked as ‘mass’, it is scanned for a pulse from the microwave cavity [3]. The program shows the pellet speed, mass and delays of these signals from firing time just after the shot. These data are saved in a separate text file to insert them into a database. Fig. 3 shows two time traces*/the signals from light barriers and from microwave cavity, and the scheme of measurements.
Fig. 3. Plot of the signals from light barriers and from microwave cavity. The scheme of pellet parameters measurement.
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3. Pellet injector control The pellet injector control uses three embedded cards: (1) 32 channels 100 kHz isolated ADC card; (2) 64 channels isolated digital I/O card; and (3) 16 channels 16 bits analogue output card. The control program provides analogue data recording, digital input/output and a 16 channels digital temperature control. The program is realised as a state machine */a sequence of any number of states. The minimal state duration is one tick of the main time sequence, chosen as 0.1 s for operations. The program configuration is divided into two parts */main configuration and scenario. The main configuration contains analogue and digital signal connections and assignments, ADC sensitivity settings, separate temperature controller settings for each barrel, signal conversion files and other common settings. The conversion files are used to translate raw ADC data into physical values */temperature, pressure. Fig. 4 shows the main program window / barrel temperatures are shown in K. The program can be switched into a manual mode / all equipment of the pellet injector is controlled by dialog buttons.
Fig. 4. Main window of pellet injector control program.
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S. Shibaev, K.B. Axon / Fusion Engineering and Design 66 /68 (2003) 893 /897
The state sequences are stored in separate files */the scenarios. Each state has different digital output and separate temperature settings for each barrel. Digital output is used mostly to control injector valves. The scenario settings may include conditional digital output to connect external controllers, pressure controller, for example. In addition to a constant digital output during the state, the program can generate a pulse at the state’s start on any digital output. The scenario file contains temperature settings for each barrel in each state. All settings are made in configuration dialogs with graphical temperature editor. The temperature control can be disabled in some states; it is always disabled in stand-by state. It disables automatically if temperature of the barrel is too high for pellet preparation. The temperature controller is realised as universal proportional-integral-derivative (PID) compensator with fully configurable parameters. The thermal characteristics of barrels and cooling facility are unknown or strongly nonlinear dependent on helium flow and on heating power, which is why an experimental way is chosen for determination of feedback parameters. The compensator parameters are found in open-loop experiments using the Chien-Hrones-Reswich method [4]. These experiments are made using a variant of the same control program. Because a better time resolution is needed for these experiments this variant uses 10 ms time steps and the scenario editor configures output voltages instead of temperatures. The feedback parameters are different for each temperature controller. The centre temperature controllers are configured mostly as proportional-integral and outer ones as proportional. Fig. 5 shows time traces of reference (fixed in scenario) and measured temperature, and controller output signal */heater voltage. As a result of a universal program structure, the configuration user interface is rather complicatedthe program configuration dialog contains seven pages and the scenario editor contains three pages. There is context-sensitive help for each page of configuration. This complexity is required for the development stage and the settings proved to be spare could be removed easily.
Fig. 5. The time traces of reference (fixed in scenario) and measured centre temperature (upper plot), and of the controller output-heater voltage.
4. Pellet injection into MAST Both programs */data acquisition and injector control work conjointly; they are linked by Windows messages. Both programs can be run alone and provide all their functions. When injector control program starts pellet preparation it becomes the master program and takes full control of data acquisition program. Fig. 6 shows a simplified diagram of the system operation. The system receives two trigger signals from MAST.
Fig. 6. The diagram of shot sequence.
S. Shibaev, K.B. Axon / Fusion Engineering and Design 66 /68 (2003) 893 /897
First trigger (about 110 s before shot) starts pellet preparation. When pellets are ready the injector control program switches to a waiting state. This state waits for second trigger up to state’s duration (usually set as 3 min). On receiving the second trigger (t//2.5 s) the injector control program switches to ‘fire’ state and arms data acquisition program. The data acquisition and pellet are started by the third MAST trigger (t//0.1 s) or a signal delayed from the second trigger. After the shot, the system acquires a shot number from the central computer, writes the data file, and transfers it to the central archive.
5. Conclusions A new highly adaptable control and data acquisition system has been developed for the MAST multi-barrel pellet injector. The system provides independent digital control of the preparation of each pellet, integrates the pellet injector with the MAST shot cycle and records data of the pellet preparation process and of pellets fired. The system is made very flexible in view of possible extensions and alterations.
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Acknowledgements This work is jointly funded by the UK Department of Trade and Industry and EURATOM. We are grateful to FOM (The Netherlands) for providing the pellet injector, and to colleagues at Risø for performing the modifications to the barrels.
References [1] M. Cox, The mega amp spherical tokamak, Fusion Eng. Des. 46 (1999) 397 /404. [2] H. Sorensen, B. Sass, K.-V. Wieseberg, A.A.M. Oomens, G. van Dijk, A.J.H. Tielemans, A multishot pellet injector for RTP, Proceedings of the Seventeenth Symposium on Fusion Technology, Rome, Italy, 1992, vol. 1, pp. 647 /650. [3] H. Sorensen, J.E. Hansen, P. Michelsen, B. Sass, K.-V. Weisberg, O. Knudsen, E. Michelsen, A microwave cavity for measurement of the mass of hydrogen pellets, Rev. Sci. Instrum. 61 (1990) 3464 /3466. [4] R.T. Stefani, B. Shahian, C.J. Savant, Jr., G.H. Hostetter, Design of Feedback Control Systems, Oxford University Press, New York and Oxford, 2002, pp. 223 /231.
Control and data acquisition system for multi-barrel pellet injector S. Shibaev *, K.B. Axon EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, UK
Abstract A control and data acquisition system has been developed for the Mega-Amp Spherical Tokamak (MAST) multibarrel pellet injector to allow reliable operation with multiple pellet sizes. The system operates with one PC running Windows NT with four embedded PCI cards. All measurements and control functions are implemented on a PC. The system software consists of two programs. The first program provides pellet firing and registration of up to four fast signals associated with each pellet /pellet speed, mass, and other signals. The second program controls pellet preparation and all the pellet injector equipment. This program is realised as state machine */allowing a sequence of any number of states, it includes independent digital PID control of the temperature of each barrel. Both programs run conjointly using message exchange. The system is integrated and synchronised with the MAST control and data acquisition systems. # 2003 S. Shibaev. Published by Elsevier B.V. All rights reserved. Keywords: MAST; Pellet injector; Data acquisition; Digital control
1. Introduction The MAST [1] eight barrels pneumatic pellet injector was built at Risø [2] for use on the RTP tokamak. It was transferred to MAST and the barrels are enlarged at Risø to suit the higher fuelling rate needed for MAST. It prepares pellets in situ in eight barrels simultaneously. The modified injector has two small barrels */1.1 mm in diameter, two large */1.7 mm, and four medium */ 1.35 mm. The injector control and measurement system was originally made using a PLC and a * Corresponding author. Tel.: /44-1235-466-657; fax: /441235-466-379. E-mail address: [email protected] (S. Shibaev).
G64 computer; the pellet preparation was controlled by two analogue temperature controllers with common settings for four barrels. This paper describes an improved system to match the new barrel configuration and to incorporate the injector into MAST operations. The new system for pellet injector control and data acquisition has been made in three phases. The first task in adapting the pellet injector for MAST operation was to provide for pellet firing and recording pellet parameters. This was implemented prior to first use of the pellet injector on MAST. During first experiment a limitation of the original control system became obvious */there was no recording of pellet preparation temperatures; changes in configuration were very difficult
0920-3796/03/$ - see front matter # 2003 S. Shibaev. Published by Elsevier B.V. All rights reserved. doi:10.1016/S0920-3796(03)00372-7
894
S. Shibaev, K.B. Axon / Fusion Engineering and Design 66 /68 (2003) 893 /897
(needing PLC re-programming). The second phase included replacement of the PLC and the G64 computer by a PC with two embedded cards */ analogue input and digital I/O */to allow flexible control and recording pellet preparation parameters. Finally, the temperature recording showed an imperfection of the original analogue temperature controller with the new barrels */it was not stable for all barrels and unable to control the temperature with sufficient precision and reproducibility. Besides, common settings for four barrels proved unsatisfactory. The third phase therefore included replacement of the original temperature controller by a 16 channels digital controller to control centre and outer temperatures of eight barrels. The centre controller adjusts the temperature of pellet preparation, whereas the outer controller provides the necessary temperature gradient. The essential improvement in the new system is the collection of all signals and control functions in one PC, which makes easy any changes in configuration. The system includes simple interface modules */linear amplifiers for analogue output and level converters for digital output. In view of possible extensions, the system is made in very general way fully using resources of embedded cards. Most of the user interface is completely general, only few parts (the mimics, for example) are specific for the pellet injector. The system hardware-PC with embedded cards, is selected, as most cost effective. The Windows NT platform provides faster program development with a convenient user interface.
Fig. 1. The scheme of data acquisition and pellet firing.
long gate pulse and short pulses for pellet firing as the digital output. To determine an accuracy of this system the delay between the trigger pulse and the output pulse is measured. Fig. 2 shows the additional delay of the first pulse in microseconds plotted as a function of fixed delay in ms. All measurements were made on the PC used for operations */an industrial PC with Athlon 750 MHz processor. The error bars show standard deviation of 20 samples in each point. The standard deviation of delay between two output pulses is less than 3 ms in the whole range of delays tested from 3 ms to 1 s. The whole error of pellet firing consists of a constant /180 ms shift of output pulse sequence and a random error of less than 10 ms. This shift is a sum of the interrupt and digital output propaga-
2. Pellet firing and data acquisition This part of the system is realised using a PCI ADC card. The card includes four channels 20 MHz ADC and 24 digital I/O channels. The control program logic is shown in Fig. 1. The MAST trigger starts acquisition, which continues to cover all data windows associated with pellet firing. The card generates an interrupt when the on-board data buffer is full. A timing thread acquires this interrupt. The thread generates a
Fig. 2. Additional delay of the first output pulse as a function of fixed delay.
S. Shibaev, K.B. Axon / Fusion Engineering and Design 66 /68 (2003) 893 /897
tion times. The random error is caused by the computer processes and system clock granularity. This result shows that the PC running Windows NT can control real time processes with accuracy of the order of 10 ms, keeping in mind that there is a delay of the order of 100 ms from the input to the computer process, and from the process and the output. The control program writes data from the four analogue channels into a data file and transfers this file to the MAST archive. This file contains also an item with pellet firing times. The program processes data before writing; it extracts fixed data windows associated with pellet firing times. There are two special settings for pellet data processing. If a channel is marked as ‘speed’, the whole range of data between two pellets is scanned for two pulses from light barriers. The delay between these pulses gives the pellet speed. If a channel is marked as ‘mass’, it is scanned for a pulse from the microwave cavity [3]. The program shows the pellet speed, mass and delays of these signals from firing time just after the shot. These data are saved in a separate text file to insert them into a database. Fig. 3 shows two time traces*/the signals from light barriers and from microwave cavity, and the scheme of measurements.
Fig. 3. Plot of the signals from light barriers and from microwave cavity. The scheme of pellet parameters measurement.
895
3. Pellet injector control The pellet injector control uses three embedded cards: (1) 32 channels 100 kHz isolated ADC card; (2) 64 channels isolated digital I/O card; and (3) 16 channels 16 bits analogue output card. The control program provides analogue data recording, digital input/output and a 16 channels digital temperature control. The program is realised as a state machine */a sequence of any number of states. The minimal state duration is one tick of the main time sequence, chosen as 0.1 s for operations. The program configuration is divided into two parts */main configuration and scenario. The main configuration contains analogue and digital signal connections and assignments, ADC sensitivity settings, separate temperature controller settings for each barrel, signal conversion files and other common settings. The conversion files are used to translate raw ADC data into physical values */temperature, pressure. Fig. 4 shows the main program window / barrel temperatures are shown in K. The program can be switched into a manual mode / all equipment of the pellet injector is controlled by dialog buttons.
Fig. 4. Main window of pellet injector control program.
896
S. Shibaev, K.B. Axon / Fusion Engineering and Design 66 /68 (2003) 893 /897
The state sequences are stored in separate files */the scenarios. Each state has different digital output and separate temperature settings for each barrel. Digital output is used mostly to control injector valves. The scenario settings may include conditional digital output to connect external controllers, pressure controller, for example. In addition to a constant digital output during the state, the program can generate a pulse at the state’s start on any digital output. The scenario file contains temperature settings for each barrel in each state. All settings are made in configuration dialogs with graphical temperature editor. The temperature control can be disabled in some states; it is always disabled in stand-by state. It disables automatically if temperature of the barrel is too high for pellet preparation. The temperature controller is realised as universal proportional-integral-derivative (PID) compensator with fully configurable parameters. The thermal characteristics of barrels and cooling facility are unknown or strongly nonlinear dependent on helium flow and on heating power, which is why an experimental way is chosen for determination of feedback parameters. The compensator parameters are found in open-loop experiments using the Chien-Hrones-Reswich method [4]. These experiments are made using a variant of the same control program. Because a better time resolution is needed for these experiments this variant uses 10 ms time steps and the scenario editor configures output voltages instead of temperatures. The feedback parameters are different for each temperature controller. The centre temperature controllers are configured mostly as proportional-integral and outer ones as proportional. Fig. 5 shows time traces of reference (fixed in scenario) and measured temperature, and controller output signal */heater voltage. As a result of a universal program structure, the configuration user interface is rather complicatedthe program configuration dialog contains seven pages and the scenario editor contains three pages. There is context-sensitive help for each page of configuration. This complexity is required for the development stage and the settings proved to be spare could be removed easily.
Fig. 5. The time traces of reference (fixed in scenario) and measured centre temperature (upper plot), and of the controller output-heater voltage.
4. Pellet injection into MAST Both programs */data acquisition and injector control work conjointly; they are linked by Windows messages. Both programs can be run alone and provide all their functions. When injector control program starts pellet preparation it becomes the master program and takes full control of data acquisition program. Fig. 6 shows a simplified diagram of the system operation. The system receives two trigger signals from MAST.
Fig. 6. The diagram of shot sequence.
S. Shibaev, K.B. Axon / Fusion Engineering and Design 66 /68 (2003) 893 /897
First trigger (about 110 s before shot) starts pellet preparation. When pellets are ready the injector control program switches to a waiting state. This state waits for second trigger up to state’s duration (usually set as 3 min). On receiving the second trigger (t//2.5 s) the injector control program switches to ‘fire’ state and arms data acquisition program. The data acquisition and pellet are started by the third MAST trigger (t//0.1 s) or a signal delayed from the second trigger. After the shot, the system acquires a shot number from the central computer, writes the data file, and transfers it to the central archive.
5. Conclusions A new highly adaptable control and data acquisition system has been developed for the MAST multi-barrel pellet injector. The system provides independent digital control of the preparation of each pellet, integrates the pellet injector with the MAST shot cycle and records data of the pellet preparation process and of pellets fired. The system is made very flexible in view of possible extensions and alterations.
897
Acknowledgements This work is jointly funded by the UK Department of Trade and Industry and EURATOM. We are grateful to FOM (The Netherlands) for providing the pellet injector, and to colleagues at Risø for performing the modifications to the barrels.
References [1] M. Cox, The mega amp spherical tokamak, Fusion Eng. Des. 46 (1999) 397 /404. [2] H. Sorensen, B. Sass, K.-V. Wieseberg, A.A.M. Oomens, G. van Dijk, A.J.H. Tielemans, A multishot pellet injector for RTP, Proceedings of the Seventeenth Symposium on Fusion Technology, Rome, Italy, 1992, vol. 1, pp. 647 /650. [3] H. Sorensen, J.E. Hansen, P. Michelsen, B. Sass, K.-V. Weisberg, O. Knudsen, E. Michelsen, A microwave cavity for measurement of the mass of hydrogen pellets, Rev. Sci. Instrum. 61 (1990) 3464 /3466. [4] R.T. Stefani, B. Shahian, C.J. Savant, Jr., G.H. Hostetter, Design of Feedback Control Systems, Oxford University Press, New York and Oxford, 2002, pp. 223 /231.