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Embedded design based virtual instrument program for positron beam automation
Applied Surface Science 255 (2008) 104–107
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Embedded design based virtual instrument program for positron beam automation J. Jayapandian, K. Gururaj, S. Abhaya, J. Parimala, G. Amarendra * Material Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, TN, India
A R T I C L E I N F O
A B S T R A C T
Article history:
Automation of positron beam experiment with a single chip embedded design using a programmable system on chip (PSoC) which provides easy interfacing of the high-voltage DC power supply is reported. Virtual Instrument (VI) control program written in Visual Basic 6.0 ensures the following functions (i) adjusting of sample high voltage by interacting with the programmed PSoC hardware, (ii) control of personal computer (PC) based multi channel analyzer (MCA) card for energy spectroscopy, (iii) analysis of the obtained spectrum to extract the relevant line shape parameters, (iv) plotting of relevant parameters and (v) saving the file in the appropriate format. The present study highlights the hardware features of the PSoC hardware module as well as the control of MCA and other units through programming in Visual Basic. ß 2008 Elsevier B.V. All rights reserved.
Available online 22 May 2008 Keywords: PSoC MCA Virtual Instrument Line shape
1. Introduction Variable low-energy positron beams are useful for obtaining information about the depth-resolved distribution of the defects at the near-surface and interface regions of materials [1,2]. In this technique, positrons of tunable energies are implanted into the material under study. The implanted positrons thermalize quickly and annihilate with the electrons of the material giving out a characteristic gamma rays of energy of 511 keV. The depth at which the positrons are implanted is determined by the positron beam energy. Due to finite momentum distribution of the electrons, the annihilation gamma energy is Doppler broadened. The Doppler broadening of the annihilation radiation is quantified by a line shape parameter called S-parameter, which provides information pertaining to open volume defects in the sample. A plot of S-parameter versus positron beam energy gives a direct depth profile of open volume defects in the material under study. Similarly, complementary W-parameter signifies the annihilation events with core electrons. The slow positron flux attainable with laboratory beams is around 105 positrons per second and the Doppler S-parameter needs to be measured at intermediate beam energies in the range of 0–30 keV. This leads to a very long measurement times and each experiment runs for a long time necessitating the automation of the positron beam experiments. Such an automated experiment
* Corresponding author. E-mail address: [email protected] (G. Amarendra). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.05.280
already existed with our positron system [2], but it was very limited in its functionality and hence more effective automation program has been implemented recently. 2. Design details The hardware required for the making this automation was (i) high-voltage unit, (ii) PC compatible MCA plug-in card and (iii) programmable system on chip (PSoC) design for controlling the high-voltage unit [3]. The schematic of the low-energy positron beam automation is shown in Fig. 1. The automation program uses a M/S ‘‘Bertan’’ make variable DC high-voltage power supply (0–50 kV) with an analog programmable port [4]. This programmable port is used for the remote setting and sensing of the high voltage. The MCA card used for the automation was the Series 5000 MCArd, developed by the APTECNRC INC., USA [5]. The MCA card comes with the built-in onboard amplifier, ADC, memory and test pulsers and provides several features like near Gaussian shaping, automatic active gated base line restoration circuit, pulse pile up rejecter, live time correct circuits etc. This MCA card is compatible with any personal computer. 3. Hardware implementation of PSoC A PSoC device consists of 12 analog and 8 digital blocks on a single chip as shown in Fig. 2. The blocks can be programmed with proper connectivity between them, may be configured to achieve a
J. Jayapandian et al. / Applied Surface Science 255 (2008) 104–107
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Fig. 1. Schematic of positron beam automation.
system on chip. PSoC devices have an array of 12 analog PSoC blocks that may work together or alone. Many analog user modules are available in the PSoC designer tool; examples include band pass filters, programmable gain amplifiers, instrumentation amplifiers, analog to digital converts (ADC), and digital to analog converters (DAC). PSoC devices have an array of eight digital PSoC blocks. Each digital PSoC block may be used autonomously as an 8-bit function or combined with other digital PSoC blocks to form 16, 24, or 32-bit functions. Many digital user modules are available; examples include timers, counter, UART, and SPI, etc. In our system, we have used, PSoC (8-pin DIP) device (CY8C27143) which utilizes the ADCINC12 (a 12-bit ADC) User Module, a PWM16 User Module with an external RC filter to get a 16-bit DAC, a PGA User Module for the preamplifier function, and a UART digital Communication User Module for serial communication between the PC and RS232. Through the PC’s serial port, the PSoC acquires data using the PGA and ADCINC12 User Modules and controls the required parameters using the PWM16 with an external RC filter (R = 1k and C = 47 mF), performs DAC with 16-bit resolution, to provide an
analog output from 0 to 5 V. For sensing the high voltage, a 12-bit ADC is configured using analog block. The design requires a suitable amplifier to amplify the sense analog signal. The amplified signal is then digitized with a 12-bit resolution ADC before being sent to the PC for display. A PGA is placed in analog block, ACB01, with suitable gain and reference to the reference analog ground created using the Ref_Mux User Module placed in the ACB00 block. The PGA output is connected to the input of the 12-bit incremental ADC for digitizing. The ADCINC12 uses analog block ASD11 and digital blocks DBB10 (TMR) and DBB11 (control); the PWM16 uses DBB00 (LSB) and DBB01 (MSB). Communication between the PSoC device and the PC through the RS232 port is done by the UART placed at DCB12 (Tad) and DCB13 (Red). The UART is set to operate at 115,200 baud by the counter output, placed in digital block DCB03. The counter user module receives the clock from global resource VC1 in the PSoC designer and divides it for 115k-baud rate operation for the UART. The power supply receives its control/ programming voltage from the 16-bit PWM module and controls the voltage using the 16-bit PWM signal with an external RC filter to provide an analog output from 0 to 5 V. The ‘‘Betran’’ make high-
Fig. 2. Block diagram of the PSoC high-voltage controller.
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J. Jayapandian et al. / Applied Surface Science 255 (2008) 104–107
Fig. 3. Pin connectivity and user module connections for PSoC.
Fig. 4. Flow chart for embedded design automation of positron beam.
J. Jayapandian et al. / Applied Surface Science 255 (2008) 104–107
107
4. Program flow As depicted in the flow chart in Fig. 4, the automation program expects the user to enter the various experimental settings like the initial and final high voltages, the time of acquisition for each run, the incremental value of the high voltage, the number of channels to which the MCA must be set up, the filename and the username etc. With this information provided, the automation program starts at the desired initial value and also starting the MCA’s data acquisition. After each acquisition, the MCA’s data is retrieved into the front end, relevant line shape parameters are calculated from the obtained spectrum, and are displayed in the tabular format and also as Origin plots. This process repeats for every high voltage unit. The system also does the automatic calibration of the MCA card and calculation of the energy resolution of the germanium detector. 5. Results and performance Fig. 5. S-parameter vs. positron beam energy plot of Ar implanted Al.
voltage power supply’s output 0–50 kV is controlled by this analog 0–5 V. The embedded system is powered from the reference voltage provided in the HV power supply itself, which provides additional safety in case of any power fluctuations. The analog and digital user module placement and pin connectivity for the automation design of the PSoC module is shown in Fig. 3. The PSoC system will be looking for the serial interrupt, and according to the commands provided in the switch statement, at the end of the code block, gives the option to select either to sense, control, or set to zero. The string ‘H’ provides analog output for controlling the voltage, ‘S’ starts the ADC to acquire sense voltage from the HV unit, ‘R’ stops the ADC read function and ‘Z’ makes the high-voltage power supply to reset to zero. The automation program developed in Visual Basic communicates with the PSoC module through serial port at a baud rate of 115,200. This communication with serial port is done by using the ‘‘Serial Port ActiveX control’’ which is shipped along with the Visual Basic programming environment. The initialization of the PSoC module, the setting up of high voltage and sensing of the high voltage are all carried out by sending the appropriate commands through the serial port. The communication of our Visual Basic application with the ‘‘APTEC’’ make MCA card has been established through a set of DDE (dynamic data exchange, a data exchange technology for windows based applications to exchange data with each other) commands offered by the APTEC software. The setting up of the MCA card, the starting and stopping of the data acquisition and all such remote communication with the MCA card like The selection of regions of interest, the background subtraction, the sum of counts in the region of interest etc. were also carried out by using various DDE commands provided by APTEC software without actually having to open the MCA operations window.
The PSoC module and the automation program have been tested independently and integrated into the beam system. The results were found to be satisfactory. The operation of desired high voltage and the control of the MCA are found to be proper. The Sparameters and W-parameters provided by the automation system are found satisfactory, and in accordance with the expectation. The energy resolution of the germanium detector was found to be 1.45 keV and the energy calibration of the MCA card was found to be 95 eV/channel, when the number of channels chosen was 4096. The first system that was studied on this new automation software was the 130 keV argon irradiated aluminum. One such plot for comparison of performance of the earlier and the present PSoC based system is shown in Fig. 5. The experimental results are found to be satisfactory. 6. Summary and conclusion Virtual instrumentation program of variable low-energy positron beam automation has been carried by using programmable system on chip. The control program controls the operations of the MCA card, the high-voltage unit and the other application software, providing the relevant parameters of interest, even as the acquisition is going on. This real time data acquisition is functioning satisfactorily in carrying out the experiments in a smooth and unattended manner. References [1] P.J. Schultz, K.G. Lynn, Rev. Mod. Phys. 60 (1988) 701. [2] G. Amarendra, B. Viswanathan, G. Venugopal Rao, J. Parimala, B. Purniah, Current Sci. 73 (1997) 409. [3] J. Jayapandian, Application Note AN2335, Cypress Microsystem, 21st July 2006. [4] User Manual of High-Voltage unit manufactured by M/s Bertan Associates Inc. [5] User manual of Series 5000 MCArd, manufactured by APTEC Instruments Inc.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Embedded design based virtual instrument program for positron beam automation J. Jayapandian, K. Gururaj, S. Abhaya, J. Parimala, G. Amarendra * Material Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, TN, India
A R T I C L E I N F O
A B S T R A C T
Article history:
Automation of positron beam experiment with a single chip embedded design using a programmable system on chip (PSoC) which provides easy interfacing of the high-voltage DC power supply is reported. Virtual Instrument (VI) control program written in Visual Basic 6.0 ensures the following functions (i) adjusting of sample high voltage by interacting with the programmed PSoC hardware, (ii) control of personal computer (PC) based multi channel analyzer (MCA) card for energy spectroscopy, (iii) analysis of the obtained spectrum to extract the relevant line shape parameters, (iv) plotting of relevant parameters and (v) saving the file in the appropriate format. The present study highlights the hardware features of the PSoC hardware module as well as the control of MCA and other units through programming in Visual Basic. ß 2008 Elsevier B.V. All rights reserved.
Available online 22 May 2008 Keywords: PSoC MCA Virtual Instrument Line shape
1. Introduction Variable low-energy positron beams are useful for obtaining information about the depth-resolved distribution of the defects at the near-surface and interface regions of materials [1,2]. In this technique, positrons of tunable energies are implanted into the material under study. The implanted positrons thermalize quickly and annihilate with the electrons of the material giving out a characteristic gamma rays of energy of 511 keV. The depth at which the positrons are implanted is determined by the positron beam energy. Due to finite momentum distribution of the electrons, the annihilation gamma energy is Doppler broadened. The Doppler broadening of the annihilation radiation is quantified by a line shape parameter called S-parameter, which provides information pertaining to open volume defects in the sample. A plot of S-parameter versus positron beam energy gives a direct depth profile of open volume defects in the material under study. Similarly, complementary W-parameter signifies the annihilation events with core electrons. The slow positron flux attainable with laboratory beams is around 105 positrons per second and the Doppler S-parameter needs to be measured at intermediate beam energies in the range of 0–30 keV. This leads to a very long measurement times and each experiment runs for a long time necessitating the automation of the positron beam experiments. Such an automated experiment
* Corresponding author. E-mail address: [email protected] (G. Amarendra). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.05.280
already existed with our positron system [2], but it was very limited in its functionality and hence more effective automation program has been implemented recently. 2. Design details The hardware required for the making this automation was (i) high-voltage unit, (ii) PC compatible MCA plug-in card and (iii) programmable system on chip (PSoC) design for controlling the high-voltage unit [3]. The schematic of the low-energy positron beam automation is shown in Fig. 1. The automation program uses a M/S ‘‘Bertan’’ make variable DC high-voltage power supply (0–50 kV) with an analog programmable port [4]. This programmable port is used for the remote setting and sensing of the high voltage. The MCA card used for the automation was the Series 5000 MCArd, developed by the APTECNRC INC., USA [5]. The MCA card comes with the built-in onboard amplifier, ADC, memory and test pulsers and provides several features like near Gaussian shaping, automatic active gated base line restoration circuit, pulse pile up rejecter, live time correct circuits etc. This MCA card is compatible with any personal computer. 3. Hardware implementation of PSoC A PSoC device consists of 12 analog and 8 digital blocks on a single chip as shown in Fig. 2. The blocks can be programmed with proper connectivity between them, may be configured to achieve a
J. Jayapandian et al. / Applied Surface Science 255 (2008) 104–107
105
Fig. 1. Schematic of positron beam automation.
system on chip. PSoC devices have an array of 12 analog PSoC blocks that may work together or alone. Many analog user modules are available in the PSoC designer tool; examples include band pass filters, programmable gain amplifiers, instrumentation amplifiers, analog to digital converts (ADC), and digital to analog converters (DAC). PSoC devices have an array of eight digital PSoC blocks. Each digital PSoC block may be used autonomously as an 8-bit function or combined with other digital PSoC blocks to form 16, 24, or 32-bit functions. Many digital user modules are available; examples include timers, counter, UART, and SPI, etc. In our system, we have used, PSoC (8-pin DIP) device (CY8C27143) which utilizes the ADCINC12 (a 12-bit ADC) User Module, a PWM16 User Module with an external RC filter to get a 16-bit DAC, a PGA User Module for the preamplifier function, and a UART digital Communication User Module for serial communication between the PC and RS232. Through the PC’s serial port, the PSoC acquires data using the PGA and ADCINC12 User Modules and controls the required parameters using the PWM16 with an external RC filter (R = 1k and C = 47 mF), performs DAC with 16-bit resolution, to provide an
analog output from 0 to 5 V. For sensing the high voltage, a 12-bit ADC is configured using analog block. The design requires a suitable amplifier to amplify the sense analog signal. The amplified signal is then digitized with a 12-bit resolution ADC before being sent to the PC for display. A PGA is placed in analog block, ACB01, with suitable gain and reference to the reference analog ground created using the Ref_Mux User Module placed in the ACB00 block. The PGA output is connected to the input of the 12-bit incremental ADC for digitizing. The ADCINC12 uses analog block ASD11 and digital blocks DBB10 (TMR) and DBB11 (control); the PWM16 uses DBB00 (LSB) and DBB01 (MSB). Communication between the PSoC device and the PC through the RS232 port is done by the UART placed at DCB12 (Tad) and DCB13 (Red). The UART is set to operate at 115,200 baud by the counter output, placed in digital block DCB03. The counter user module receives the clock from global resource VC1 in the PSoC designer and divides it for 115k-baud rate operation for the UART. The power supply receives its control/ programming voltage from the 16-bit PWM module and controls the voltage using the 16-bit PWM signal with an external RC filter to provide an analog output from 0 to 5 V. The ‘‘Betran’’ make high-
Fig. 2. Block diagram of the PSoC high-voltage controller.
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J. Jayapandian et al. / Applied Surface Science 255 (2008) 104–107
Fig. 3. Pin connectivity and user module connections for PSoC.
Fig. 4. Flow chart for embedded design automation of positron beam.
J. Jayapandian et al. / Applied Surface Science 255 (2008) 104–107
107
4. Program flow As depicted in the flow chart in Fig. 4, the automation program expects the user to enter the various experimental settings like the initial and final high voltages, the time of acquisition for each run, the incremental value of the high voltage, the number of channels to which the MCA must be set up, the filename and the username etc. With this information provided, the automation program starts at the desired initial value and also starting the MCA’s data acquisition. After each acquisition, the MCA’s data is retrieved into the front end, relevant line shape parameters are calculated from the obtained spectrum, and are displayed in the tabular format and also as Origin plots. This process repeats for every high voltage unit. The system also does the automatic calibration of the MCA card and calculation of the energy resolution of the germanium detector. 5. Results and performance Fig. 5. S-parameter vs. positron beam energy plot of Ar implanted Al.
voltage power supply’s output 0–50 kV is controlled by this analog 0–5 V. The embedded system is powered from the reference voltage provided in the HV power supply itself, which provides additional safety in case of any power fluctuations. The analog and digital user module placement and pin connectivity for the automation design of the PSoC module is shown in Fig. 3. The PSoC system will be looking for the serial interrupt, and according to the commands provided in the switch statement, at the end of the code block, gives the option to select either to sense, control, or set to zero. The string ‘H’ provides analog output for controlling the voltage, ‘S’ starts the ADC to acquire sense voltage from the HV unit, ‘R’ stops the ADC read function and ‘Z’ makes the high-voltage power supply to reset to zero. The automation program developed in Visual Basic communicates with the PSoC module through serial port at a baud rate of 115,200. This communication with serial port is done by using the ‘‘Serial Port ActiveX control’’ which is shipped along with the Visual Basic programming environment. The initialization of the PSoC module, the setting up of high voltage and sensing of the high voltage are all carried out by sending the appropriate commands through the serial port. The communication of our Visual Basic application with the ‘‘APTEC’’ make MCA card has been established through a set of DDE (dynamic data exchange, a data exchange technology for windows based applications to exchange data with each other) commands offered by the APTEC software. The setting up of the MCA card, the starting and stopping of the data acquisition and all such remote communication with the MCA card like The selection of regions of interest, the background subtraction, the sum of counts in the region of interest etc. were also carried out by using various DDE commands provided by APTEC software without actually having to open the MCA operations window.
The PSoC module and the automation program have been tested independently and integrated into the beam system. The results were found to be satisfactory. The operation of desired high voltage and the control of the MCA are found to be proper. The Sparameters and W-parameters provided by the automation system are found satisfactory, and in accordance with the expectation. The energy resolution of the germanium detector was found to be 1.45 keV and the energy calibration of the MCA card was found to be 95 eV/channel, when the number of channels chosen was 4096. The first system that was studied on this new automation software was the 130 keV argon irradiated aluminum. One such plot for comparison of performance of the earlier and the present PSoC based system is shown in Fig. 5. The experimental results are found to be satisfactory. 6. Summary and conclusion Virtual instrumentation program of variable low-energy positron beam automation has been carried by using programmable system on chip. The control program controls the operations of the MCA card, the high-voltage unit and the other application software, providing the relevant parameters of interest, even as the acquisition is going on. This real time data acquisition is functioning satisfactorily in carrying out the experiments in a smooth and unattended manner. References [1] P.J. Schultz, K.G. Lynn, Rev. Mod. Phys. 60 (1988) 701. [2] G. Amarendra, B. Viswanathan, G. Venugopal Rao, J. Parimala, B. Purniah, Current Sci. 73 (1997) 409. [3] J. Jayapandian, Application Note AN2335, Cypress Microsystem, 21st July 2006. [4] User Manual of High-Voltage unit manufactured by M/s Bertan Associates Inc. [5] User manual of Series 5000 MCArd, manufactured by APTEC Instruments Inc.