Autotuning and goniometer controller

The ATC-400 controller unit can be used as a standalone device, i.e. as a wobbler, to tune any RF resonant circuit. This is particularly useful in the preparation phase of an NMR experiment whenever user designed RF coils are used in order to improve the S/N ratio or to expand the frequency range of the probe tunability.

The controller unit is based on the industrial-grade CompactPCI platform fitted with Intel Core 2 Duo CPU blade and digital RF synthesizer. A separate internal power supply provides power to integrated RF reflecometer and stepper motor controller and drive units.

The ATM-C4G stepper motor unit is powered directly from the ATC-400 via a single cable harness. The controller also provides power, control, and RF tuning signal for the ATC-500 RF switch via two additional cables. Complete wiring of the AT-PMSC-1 autotuning system into an existing NMR spectrometer is thus achieved by solely three, ready to use, flexible cables. Moreover, cabling lengths can be as much as 20m or more since optically-coupled and differential-type signalling is employed. Distant positioning of the NMR magnet, across a large lab from the NMR spectrometer, therefore presents no problem for the installation of the AT-PMSC-1 autotuning system.

Through the ATC-400 touchscreen user interface, up to 4 trimmers and the goniometer of the ATP-CF probe can be controlled. The main screen of the interface displays a reflected RF power level vs. frequency and the orientation of the gonoimeter in real time, as well as the status bar. There are two modes of operation, the local one which, in addition to automatic tuning, allows for manual adjustment of trimmers and goniometer, and the remote one, intended for spectrometer-controlled autotuning and reorienting of samples. ATC-400 settings are controled through a separate screen, typically used to select active trimmers, to initialize the positions of trimmer and goniometer shafts, and to access the online help. Although the application software runs on top of Microsoft Windows XP, the OS is hidden from the operator’s access. The complete ATC-400 software layer can be automatically restored or upgraded by inserting a bootable USB key when the system is powered-on.

Frequency-stepping experiments in a broad frequency range (several MHz) as well as temperature-dependence experiments in a broad temperature range (several hundred K), which require precise tuning at each step, are easily performed by issuing string-based commands to the RS-232 bus from the automation.