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This group includes the readback waveform at the top. All the PVs in this group directly affect or measure the frequency generated by the tune PLL NCO.
| Name | PV | Description |
|---|---|---|
| Tune Following Frequency | :PLL:NCO:OFFSETWF | This waveform records the complete history of the Tune PLL offset frequency |
| Offset FIFO readout overrun | :PLL:NCO:FIFO_OVF | This will report an alarm status if the OFFSETWF waveform overruns. Typically this can happen if the detector dwell time is set too low. |
| Reset FIFO | :PLL:NCO:RESET_FIFO_S | This will force the OFFSETWF to discard any partially captured data. This is used to ensure that the next update received for MEAN_OFFSET is fully up to date. |
All the PVs in the NCO group directly affect or measure the frequency generated by the tune PLL NCO.
| Name | PV | Description |
|---|---|---|
| Freq | :PLL:NCO:FREQ_S | When written this will set the PLL NCO to the given frequency. If feedback is running the offset will briefly be forced to zero. |
:PLL:NCO:FREQ | This reads back the current NCO frequency. This PV updates at 10Hz. | |
| Offset | :PLL:NCO:OFFSET | This is the current PLL offset, updated at 10Hz. |
| Gain | :PLL:NCO:GAIN_S | The NCO signal strength is configured here. |
:PLL:NCO:ENABLE_S | This PV turns the NCO output on or off. | |
| Mean | :PLL:NCO:MEAN_OFFSET | This is the mean offset computed over the last full OFFSETWF waveform. |
| Std | :PLL:NCO:STD_OFFSET | This is the standard deviation computed over the last full OFFSETWF waveform. |
| Tune | :PLL:NCO:TUNE | This is the fractional tune computed from the MEAN_OFFSET value and the base frequency. This PV updates when MEAN_OFFSET updates, and is forced to NaN when feedback is not running. |
Detector
This group of PVs is used to configure the detector used to measure the response.
| Name | PV | Description |
|---|---|---|
| Source | :PLL:DET:SELECT_S | Used to configure source of data for the detector. The possible sources are as documented for :DET:SELECT_S on Detector Overview. For Tune PLL the "ADC no fill" source is recommended. |
| Gain | :PLL:DET:SCALING_S | The magnitude of values read out from the detector as reported by :PLL:FILT:MAG_DB should be greater than -84dB to avoid loss of resolution in the phase measurement, and cannot be greater than 0dB without generating overflow. The dynamic range of the detector is much larger, and this gain control allows the readout scaling to be adjusted for best results. |
| Bunches | This links to the Detector Bunch Enables screen where the detector bunches can be configured. | |
:PLL:DET:COUNT | This reports how many bunches are being measured by the detector. | |
| Dwell | :PLL:DET:DWELL_S | This configures the number of turns used to measure a single detector value. |
| Blanking | :PLL:DET:BLANKING_S | This can be set to "Ignore", in which case the blanking trigger is ignored, or to "Blanking". If "Blanking" is selected, then while the blanking trigger (configured in Trigger Configuration) is active all inputs are ignored: both the detector and the feedback controller stand still. Note that updates are still generated: this ensures that any spectral measurements made using the :PLL:NCO:OFFSETWF waveform remain accurate. |
Readbacks
The readback PVs show the current measurements from the detector, all updating at 10 Hz.
| Name | PV | Description | ||||
|---|---|---|---|---|---|---|
| I, Q |
| Detector readbacks in I and Q components. To regard the response as a complex number, compute
| ||||
| Magnitude |
| Magnitude of the detector response and converted to dB, relative to overflow at magnitude = 1.0. | ||||
| Phase | :PLL:FILT:PHASE | Phase of the detector response. | ||||
| Debug | Links to the Tune PLL Debug for a detailed view of the detector response. | |||||
:PLL:DEBUG:ENABLE_S | This PV indicates whether the debug readbacks are enabled. This readback is normally not required, and the extra processing load can usefully be avoided by leaving this disabled when not required. |