PXI Chassis Research Articles

Low level RF development for ESS high beta cavity test

Testing of superconducting cavities requires the use of a Self-Excited Loop or Phase Locked Loop in order to track a cavity’s resonant frequency under the disturbances of micro-phonics. Many laboratories have successfully developed their own Low Level RF solutions and have implemented these using Field Programmable Gate Array at the heart of the digital system. This approach has also been adopted at Daresbury Laboratory. However, the dedicated system was identified as a single point of failure in the complex operational testing infrastructure and an alternative, back-up, system was sought. Rather than duplicate the existing system another approach has been adopted making use of Commercial Off The Shelf hardware with minimal requirement for interconnect to the existing high power system. The solution is based around the NI (National Instruments Corporation) FlexRIO transceiver adapter NI-5782 connected to the NI-7962R FPGA module inside a PXI chassis. This system is capable of working directly at an Intermediate frequency of 37.5 MHz and only requires a simple up-converter / down-converter stage. Testing the high Q (typically 2 × 1010) cavities up to accelerating gradients of 22.5 MV/m has been successful.

Development of Multichannel Readout Electronics for a CsI(TI) Gamma Detection Array at ETF of Cooler Storage Ring

We present a multichannel readout electronics developed for a CsI(TI) gamma detection array with 1024 large area avalanche photodiodes at the external target facility of cooler storage ring in the institute of modern physics. The full read-out electronics consist of 32 identical analog boards, eight acquisition and control boards (ACBs), and a PXI chassis. An analog board can handle energy and time measurements for 32 channels. The ACB implements analog output signal conversion, slow control, fast timing control signals generation, and data acquisition. The energy linearity of the readout electronics is better than 0.2% in the dynamic range of 0.06–0.60 V. The relative resolution of intrinsic electronics is about 0.24% at output voltage of 0.57 V.

Clock and trigger distribution for CBM-TOF quality evaluation of RPC super module detector assemblies

RPC Super module (SM) detector assemblies are used for charged hadron identification in the Time-of-Flight (TOF) spectrometer at the Compressed Baryonic Matter (CBM) experiment. Each SM contains several multi-gap Resistive Plate Chambers (MRPCs) and provides up to 320 electronic channels in total for high-precision time measurements. Time resolution of the Time-to-Digital Converter (TDC) is required to be better than 20 ps. During mass production, the quality of each SM needs to be evaluated. In order to meet the requirements, the system clock signal as well as the trigger signal should be distributed precisely and synchronously to all electronics modules within the evaluation readout system. In this paper, a hierarchical clock and trigger distribution method is proposed for the quality evaluation of CBM-TOF SM detectors. In a first stage, the master clock and trigger module (CTM) allocated in a 6U PXI chassis distributes the clock and trigger signals to the slave CTM in the same chassis. In a second stage, the slave CTM transmits the clock and trigger signals to the TDC readout module (TRM) through one optical link. In a third stage, the TRM distributes the clock and trigger signals synchronously to 10 individual TDC boards. Laboratory test results show that the clock jitter at the third stage is less than 4 ps (RMS) and the trigger transmission latency from the master CTM to the TDC is about 272 ns with 11 ps (RMS) jitter. The overall performance complies well with the required specifications.

Linearity evaluation of high-speed sampling ADC board

There are growing demands on the evaluation of accuracy for high-speed analog-to-digital converters which are increasingly needed in electrical metrology these days. Here, we have developed a system to measure the linearity error of analog-to-digital converters by adopting a reference sampling voltmeter and a dummy waveform generator. With the measurement setup, we evaluated the linearities for three units of Δ-Σ analog-to-digital converter, NI-5922, combined with three different PXI chassis. We found that the maximum linearity error can change with the PXI chassis up to about 15μV/V.

Design of a New Telescope Control System for Use in Astronomical Transient Events

Robotic autonomous telescopes provide highlevel control by selecting astronomical targets for observation, and they usually run under the control of a scheduler. TalonVIEW is a newly designed robotic autonomous telescope control system (TCS) for 16 inches telescope mount for use in astronomical transient events. The telescope control algorithm was implemented in PXI chassis written in GProgramming (LabVIEW) on realtime operating system(PharLab) from scratch. A new TCP/IP library was also implemented in Talon software to communicate with Pharlab in PXI chassis. Initial setup without any permanent pier and polar alignment showed that the pointing error of the telescope has been obtained as 2.22 arcminutes (132 arcseconds) in RA axis (horizontal axis of the image) and 25 arcseconds in Dec axis (vertical axis of the image), and tracking error has been observed as 4.8 arcseconds per second.

Design of a New Telescope Control System for Use in Astronomical Transient Events

Robotic autonomous telescopes provide highlevel control by selecting astronomical targets for observation, and they usually run under the control of a scheduler. TalonVIEW is a newly designed robotic autonomous telescope control system (TCS) for 16 inches telescope mount for use in astronomical transient events. The telescope control algorithm was implemented in PXI chassis written in GProgramming (LabVIEW) on realtime operating system(PharLab) from scratch. A new TCP/IP library was also implemented in Talon software to communicate with Pharlab in PXI chassis. Initial setup without any permanent pier and polar alignment showed that the pointing error of the telescope has been obtained as 2.22 arcminutes (132 arcseconds) in RA axis (horizontal axis of the image) and 25 arcseconds in Dec axis (vertical axis of the image), and tracking error has been observed as 4.8 arcseconds per second.

FPGA Based High Speed Data Acquisition System for Electrical Impedance Tomography

Electrical Impedance Tomography (EIT) systems are used to image tissue bio-impedance. EIT provides a number of features making it attractive for use as a medical imaging device including the ability to image fast physiological processes (>60 Hz), to meet a range of clinical imaging needs through varying electrode geometries and configurations, to impart only non-ionizing radiation to a patient, and to map the significant electrical property contrasts present between numerous benign and pathological tissues. To leverage these potential advantages for medical imaging, we developed a modular 32 channel data acquisition (DAQ) system using National Instruments' PXI chassis, along with FPGA, ADC, Signal Generator and Timing and Synchronization modules. To achieve high frame rates, signal demodulation and spectral characteristics of higher order harmonics were computed using dedicated FFT-hardware built into the FPGA module. By offloading the computing onto FPGA, we were able to achieve a reduction in throughput required between the FPGA and PC by a factor of 32:1. A custom designed analog front end (AFE) was used to interface electrodes with our system. Our system is wideband, and capable of acquiring data for input signal frequencies ranging from 100 Hz to 12 MHz. The modular design of both the hardware and software will allow this system to be flexibly configured for the particular clinical application.

A Virtual Instrument for Automated Measurement of Arterial Compliance

Measurement of arterial distensibility is very important in cardiovascular diagnosis for early detection of coronary heart disease and possible prediction of future cardiac events. Conventionally, B-mode ultrasound imaging systems have been used along with expensive vessel wall tracking systems for estimation of arterial distension and calculation of various estimates of compliance. We present a simple instrument for noninvasive in vivo evaluation of arterial compliance using a single element ultrasound transducer. The measurement methodology is initially validated using a proof of concept pilot experiment using a commercial ultrasound pulser-receiver. A prototype system is then developed around a PXI chassis using LABVIEW software. The virtual instrument employs a dynamic threshold algorithm to identify the artery walls and then utilizes a correlation based tracking technique to estimate arterial distension. The end-diastolic echo signals are averaged to reduce error in the automated diameter measurement process. The instrument allows automated measurement of the various measures of arterial compliance with minimal operator intervention. The performance of the virtual instrument was first analyzed using simulated data sets to establish the maximum measurement accuracy achievable under different input signal to noise ratio (SNR) levels. The system could measure distension with accuracy better than 10 μm for positive SNR. The measurement error in diameter was less than 1%. The system was then thoroughly evaluated by the experiments conducted on phantom models of the carotid artery and the accuracy and resolution were found to meet the requirements of the application. Measurements performed on human volunteers indicate that the instrument can measure arterial distension with a precision better than 5%. The end-diastolic arterial diameter can be measured with a precision better than 2% and an accuracy of 1%. The measurement system could lead to the development of small, portable, and inexpensive equipment for estimation of arterial compliance suitable in mass screening of “at risk” patients. The automated compliance measurement algorithm implemented in the instrument requires minimal operator input. The instrument could pave the way for dedicated systems for arterial compliance evaluation targeted at the general medical practitioner who has little or no expertise in vascular ultrasonography.

Control and acquisition for MAST Thomson scattering diagnostics

The MAST (mega-amp spherical tokamak) Thomson scattering (TS) diagnostics have been radically upgraded and expanded. Eight 30 Hz 1.6 J Nd:YAG lasers have been combined to produce a sampling rate of 240 Hz. The scattered signals are acquired by two spectrometer systems: core and edge. The core system has been built anew: collection optics, polychromators, digitizers, and control computers. It allows measurement of electron temperature and density at 130 spatial points with ∼10 mm resolution across the plasma. The Nd:YAG scattered light signals are registered in 650 channels as polychromator outputs; each channel is registered on two ADCs: at 1 GHz rate in a short interval around each laser pulse and at 100 kHz for background data. The fast ADCs are combined in 26 data acquisition units. Each unit is assembled in a 6 U PXI chassis with embedded controller and six 4-channel 1 GHz ADC cards. Some chassis contain a 96-channel slow ADC card with Ethernet control. The Ruby TS has been rebuilt with a new spectrometer and CCD camera to provide higher spatial resolution – 512 points; the laser has been modified to add double pulse capability. A new control and acquisition system has been developed; it has modular design allowing flexibility and seamless expansion. The system supports event-triggered and real-time operation (will be added in a later stage). A smart trigger device has been developed for TS timing and synchronisation. It provides complex pulse sequences for laser firing with resynchronisation on a number of digital and analogue inputs including plasma events. This device also triggers TS acquisition. The system is integrated by a TS master process running on the dedicated computer; it is represented as a standard MAST data acquisition unit. The Ruby TS is also implemented as a standard MAST unit linked with the Nd:YAG TS by MAST system services.

Impedance measurement set-up based on off-the-shelf PXI modules

As bioimpedance measurements are being done in an increasing variety of measurands and environments, measurement equipment must be flexible in use and easy to handle for the researcher. Measurement equipment used today is excellent for a range of uses, but it is often bulky, heavy, and not very flexible. A new compact and flexible measurement set-up based on off-the-shelf modules is described. The system is based on commercially available PXI-modules, one module that may be custom made, and custom software. The basis of the system is a PXI chassis with a power supply unit. The chassis is equipped with a controller module running software controlling the system, a signal generator, and a multichannel digitizer. All of this is commercially available. Both a custom made and a commercially available impedance interfaces were used. A LabVIEW program is controlling the measurement system, and provides a user interface. The LabVIEW program handles necessary signal conditioning and calibration. The measurement system is capable of doing frequency response measurements at frequencies up to 15 MHz. In addition to the two normal voltage pick-up electrodes used in four-electrode measurements, this system has the possibility to use 5 extra voltage pick-up electrodes. This simplifies exploration of segmental impedance, anisotropy, reciprocity, etc.

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Clock and trigger synchronization between several chassis of digital data acquisition modules

In applications with segmented high purity Ge detectors or other detector arrays with tens or hundreds of channels, the high development cost and limited flexibility of application specific integrated circuits outweigh their benefits of low power and small size. The readout electronics typically consist of multi-channel data acquisition modules in a common chassis for power, clock and trigger distribution, and data readout. As arrays become larger and reach several hundred channels, the readout electronics have to be divided over several chassis, but still must maintain precise synchronization of clocks and trigger signals across all channels. This division becomes necessary not only because of limits given by the instrumentation standards on module size and chassis slot numbers, but also because data readout times increase when more modules share the same data bus and because power requirements approach the limits of readily available power supplies. In this paper, we present a method for distributing clocks and triggers between 4 PXI chassis containing DGF Pixie-16 modules with up to 226 acquisition channels per chassis. The data acquisition system is intended to instrument the over 600 channels of the SeGA detector array at the National Superconducting Cyclotron Laboratory. Our solution is designed to achieve synchronous acquisition of detector waveforms from all channels with a jitter of less than 1ns, and can be extended to a larger number of chassis if desired.