CAMAC system

Control of the separator will be by a microprocessor based serial CAMAC system using standard CERN interfaces, and work is progressing rapidly in this domain. A control room, close to the SC control room, is being prepared, much of the CAMAC hardware is available already, and a start has been made on the software. 

CAMAC systems are worth considering as the basic interface connecting the computer with the experiment. (See V.C.2. and V.C.3.) There are several ADC s and digitizers available as CAMAC modules which are as good as the non-CAMAC units which makes the whole thing very attractive because of the ease of adding units and of the additions being of modest cost. 

The hardware cost associated with CAMAC also represents a middle ground between a homebuilt interface and a commercially built interface. The software must still be written for the particular system as in the case of a homebuilt interface but, due to the standardization of the commands required for the modules, the task is a little easier with the CAMAC interface. Furthermore, since CAMAC modules are commercially available, any programs written for a CAMAC system can be adapted quite easily for another CAMAC system. 

CAMAC is an international standard for modular computer instrumentation. It specifies the electrical, mechanical, and functional characteristics of modular instruments to be plugged into a standard multi-receptacle "crate" which, in turn, can be interfaced to a minicomputer. The unique feature of CAMAC systems, as opposed to other modular systems, is that the modules not only get power from the crate but the "data-way" between the modules and the crate "controller" can carry 24-bits of data in each direction in addition to various function, address, and flag signals. The controller resides in the crate as a module and acts as an interface between the modules and a specific computer. Some of the lines in the dataway are location-specific so that a module in a given slot can be addressed by the controller. The modules (except for the controller) cannot communicate with other modules except through the controller. 

The spectrometer described in the last section (V.C.2.) uses a CAMAC system with mostly commercial components. It consists of a crate with 25 slots, two of which are taken up with a crate controller to interface with a Data General NOVA 1200 computer. The essential modules in the crate, in addition to the controller, are two transient digitizers (each stores 1024 8-bit words recorded at rates up to 20 MHz), one timing module, a GPIB interface, and one X-Y driver. Together with other modules which are primarily used for utility and... 

Scattering on the Triple-Axis-Diffractometer [1,2] at the HASYLAB high-energy beamline BW5 is performed in the horizontal plane using an Eulerian cradle as sample stage and a germanium solid-state detector. The beam is monochromatized by a singlecrystal monochromator (e.g. Si 111, FWHM 5.8 ), focused by various slit systems (Huber, Riso) and iron collimators and monitorized by a scintillation counter. The instrument is controlled by a p-VAX computer via CAMAC. 

The operational procedures of the chamber have recently been upgraded from manual to automatic with the installation of a dedicated computer system (Kinetic Systems Inc., CAMAC with DEC LSI 11/23 microprocessor). This allows precise and reproducible control which was impossible under manual operation. Computer assisted operation was achieved through the development of an algorithm which controls the chamber wall temperature and cooling rate while maintaining a specified differential between air and wall temperature (AT = 0.0 0.2°C). The differential is maintained by adiabatic cooling of the air caused by variation of the rate of evacuation. 

For this reason the data acquisition systems at EMBL are based on CAMAC. Fig. (22) shows schematically the data acquisition configuration as it is used in our laboratory The high degree of modularity enables a continuous expansion of the system as required by the experiments, minimizing the development of new hardware and software. 

A real-time spectral data monitor was placed in operation. The monitor consists of an independent microprocessor-based system that acquires real-time spectral data and additional housekeeping information flowing through the CAMAC/HP computer-interface lines. The complete laser-induced fluorescence spectrum produced by each laser shot is displayed in real time. The system also provides a two-channel output to an analog chart recorder that produces two profile traces (usually the laser-induced phycoerythrin and chlorophyll a spectral response peaks). 

In this spectrometer, the timing and the digitizing functions already mentioned, as well as several other functions are performed by modules located in a CAMAC crate. A discussion of CAMAC will follow in the next section (V.C.3.). Simply described, it is a commercially standardized hardware system interfaced to the minicomputer with a few hundred modules of all kinds available commercially. 

This section points out the existence, apparently not well known in NMR circles, of a middle ground between developing a computer interface from scratch and buying a data system already interfaced to the spectrometer. We have assembled such an interface using CAMAC modules which are extensively used in particle physics experiments and we give a brief description here as an example of what is possible (Fukushima and Swenson, 1980). 

The block diagram in the last section shows the spectrometer with the CAMAC modules identified. Several different experiments requiring different pulse sequences can be performed easily with such a system. A moderately complicated example is a spin-lattice relaxation time measurement in the time domain on a poly crystalline intermetallic sample containing 1=3/2 nuclei. Since a non-cubic 1=3/2 system has unequally spaced levels, special techniques must be used for relaxation time measurements (see III.C.3.) and we adopt the procedure of Avogadro and Rigamonti (1973) to initialize the populations before the magnetization recovery. 

A wide variety of counting systems has been developed for various purposes. Equipment is often built as NIM (Nuclear Instrument Module standard) or CAMAC (Computer Automated Measurement And Control standard) modules, which fit into standard bins (or crates) containing power supplies and some inter-module connections. Cable connectors are also largely standardized. This facilitates combinations of bias supplies, amplifiers, discriminators, SCAs, ADCs, counters, and other circuitry to fit any need as well as their connection to computers. Some non-standard units, e.g. portable instruments, have their own power supply, main amplifier, counter or rate-meter, etc. 

The 5x5 strip detector used in this work (Figure 1) was fabricated using a photomask technique to make the lithium and boron implants. Our laboratory data acquisition system consists of 10 spectroscopy channels, each with a 13-bit ADC, permitting strips to be analyzed individually. The ADCs are read out through a CAMAC crate with a Macintosh computer. Events are stored on disk in list-mode for subsequent processing. 

Figure 5 Components (not to scale) of a typical nuclear microprobe system (A) electrostatic particle accelerator (B) primary object aperture (C) secondary collimator (D) focusing system (E) scanning system (F) video camera and microscope (G) surface barrier detector for scattered particles (H) X-ray detector (I) specimen (J) surface barrier detector for transmitted particles (STIM) (K) front-end CAMAC with data bus (L) main computer and display with elemental map. (Reprinted with permission from Maenhaut W and Malmqvist KG (2001) Particle-induced X-ray emission analysis. In Van Grieken RE and Markowicz AA (eds.) Handbook of X-Ray Spectrometry, 2nd edn. Ch. 12, pp. 719-809. New York Dekker Marcel Dekker Inc.)...

The CMU medium energy physics group is in the process of switching from a CAMAC-based data acquisition system to the more powerful FASTBUS standard. The advantages are numerous higher densities for more cost effective modules (typically, FASTBUS modules cost l/4 li their CAMAC counterparts), suppression of invalid data for more efficient data collection, smart crate controllers for better local control of data acquisition, faster read-out, and more. 

CAMAC—A modular instrumentation system for data handling , report EUR... 

Figure 2 camac interfaced conqmter system for multi-channel y-ray spectrometry... 

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