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nmr_probes [2013/12/14 10:52] pereira |
nmr_probes [2014/11/13 12:14] pereira [Motivation] |
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Two digital oscilloscopes are dedicated to NMR readout – one for the analysis line NMRs and one for the spectrograph NMRs. The scopes are located in data-U6, in upper two shelves on the right electronics rack. They are isolated from clean ground because this signals from the NMR probes are on a dirty ground. | Two digital oscilloscopes are dedicated to NMR readout – one for the analysis line NMRs and one for the spectrograph NMRs. The scopes are located in data-U6, in upper two shelves on the right electronics rack. They are isolated from clean ground because this signals from the NMR probes are on a dirty ground. | ||
- | The NMR running programs for both the S800 analysis line and spectrograph | + | ===== Motivation ===== |
+ | Due to the location of the NMR probes in the dipoles of both the S800 analysis line and spectrograph, | ||
- | {{:wiki:NMR-control.jpg?400|NMR Control panel for the Analysis line dipoles.}} | + | The solution implemented on the S800 uses digital oscilloscopes to digitize the NMR signal. The digitized signal is then used in a program that calculates the position of the resonance and deduces the value of the magnetic field. This program (written in Tcl/Tk) is fully autonomous and automatically writes the measured Brho values to the relevant EPICS channels. In addition, it offers the possibility to match the dipoles |
+ | ===== Description ===== | ||
+ | The NMR running programs for both the S800 analysis line and spectrograph dipoles can be started by selecting the NMR option in the operation applications of the desktop **devop1**. The picture below shows the NMR panel for the S800 Analysis Line GUI as an example. The top (yellow) panel shows the data relevant to the NMR module, the middle (pink) the digitized signal from the oscilloscope and the bottom (blue) the status and measurements for the dipoles. | ||
- | The NMR program constantly checks the status of the various dipoles from the EPICS system and updates the status column. In addition, the program checks the log file at startup for the closest previously measured value. In case no previous measurement can be used the program searches for a signal around the guessed value of the field. This search can take some time if the calibration is off or the hysteresis of the dipole is large. | + | |
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+ | ===== Operation ===== | ||
+ | The NMR program constantly checks the status of the various dipoles from the EPICS system and updates the status column. In addition, the program checks the log file at startup for the closest previously measured value. In case no previous measurement can be used the program searches for a signal around the guessed value of the field. This search can take some time if the calibration is off or the hysteresis of the dipole is large. The maximum number of attempts is limited to 200. After that the status is marked as " | ||
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+ | In order to reduce the searching time, the program tries to guess the field from the following sources, in priority order: | ||
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+ | * Previous measurement if the current hasn't changed | ||
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+ | * Extrapolation from previous measurement if the change in current is within ±5% | ||
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+ | * Calibration if no previous measurement is available | ||
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+ | Once a signal is found, the measuring sequence tries to find two resonance positions on either side of 0. Each resonance is calculated as the average between the negative and positive modulation minima (blue and green curves, and corresponding arrows). The final field is interpolated from those measurements, | ||
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+ | If a dipole is turned off or its field is being changed, the status shows either " | ||
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+ | THIS FIGURE IS OBSOLETE. NEW A NEWER VERSION | ||
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+ | The magnet currents, measured fields, and deviation from the set value are logged in a file that is soft-linked from the " | ||
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+ | ===== Matching ===== | ||
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+ | The button labeled “Match” opens a new window for matching the dipoles by pairs (see picture below). The user has the possibility to match the dipoles to either Barney or to the average calculated from the present measurements. This last function is useful when the dipoles have been tweaked to adjust the position of the beam, leading to an unmatched pair of dipoles. Since matching the dipoles involves changing their fields, it is necessary to wait for the measuring loop to go over each dipole before the effect of matching can be observed. | ||
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+ | ===== Troubleshooting ===== | ||
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+ | The NMR program is connected to the following devices and systems: | ||
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+ | * The NMR module through a terminal server | ||
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+ | * The digital oscilloscope through a terminal server | ||
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+ | * The EPICS system through the caRepeater process launched by the et_wish shell running the program | ||
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+ | Any of these connections can eventually be broken, and the program tries to catch the failures and report them to the user. However there are cases when the program " | ||
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+ | In case nothing happens after clicking on the icon, the connection to the NMR module is probably locked and needs to be freed. To free it, type the following from any shell window (actual typing show in this font ): | ||
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+ | - **telnet 35.9.56.212** | ||
+ | - Enter any **username** | ||
+ | - **set priv ** | ||
+ | - The system will ask you the password (ask the S800 device physicist) | ||
+ | - **unattach port x** (where x=1 for the analysis line and x=2 for the spectrograph) | ||
+ | - **logout** | ||
+ | - Click again on the starting icon and the program should start. | ||