PID / PLL Tab¶
The PID / PLL tab is only available if the GHF-PID Quad PID/PLL Controller option is installed on the GHFLI Lock-in Amplifier (the installed options are displayed in the Device tab).
Note
The feedback controllers provide general-purpose PID functionality, phase-locked loop (PLL) functionality, and External Reference functionality. When the user sets one of the demodulators to ExtRef mode (see Lock-in tab, Demodulators section, Mode column), one of the PID controllers will be reserved for that purpose.
Note
Some settings in the PID / PLL tab are interdependent with settings that are accessible from other tabs. If the PID output controls a certain variable, e.g. Signal Output Offset, this variable will be shown as read-only where it appears in other tabs (i.e. in the Lock-in tab for this case).
Features¶
- Four fully programmable proportional, integral, derivative (PID) controllers
- Two fully programmable 1.8 GHz phased-locked loops
- Input parameters: demodulated phase, amplitude, X & Y
- Output parameters: output amplitudes, oscillator frequencies, demodulator phase
- Phase unwrap for demodulator Θ data (± 1024 π), e.g. for optical phase-locked loops
- Bandwidth limit for the derivative (D) feedback component
- Programmable PLL center frequency and phase setpoint
- Programmable PLL phase detector filter settings
- Generation of sub-multiple frequencies by use of harmonic multiplication factor
Description¶
The PID / PLL tab is the main control center for the feedback loop controllers in the instrument. Whenever the tab is closed or an additional one of the same type is needed, clicking the following icon will open a new instance of the tab.
| Control/Tool | Option/Range | Description |
|---|---|---|
| PID |  |
Features all control, analysis, and simulation capabilities of the PID controllers. |
The PID / PLL tab (see LabOne UI: PID / PLL tab) consists of four identical side-tabs, each of them providing access to the functionality of one of the four PID / PLL controllers and the associated PID Advisor.
Note
Please note that the PID Advisor will be enabled in a future LabOne release.
With their variety of different input and output connections, the LabOne PID controllers are extremely versatile and can be used in a wide range of different applications including microwave resonator characterization and control, laser locking or high-speed SPM. Figure 2 shows a block diagram of all PID controller components, their interconnections and the variables to be specified by the user.
Setting up a Control Loop¶
Depending on the application there are a number of ways to set up a control loop. To learn the core principles of Proportional-Integral-Derivative (PID) Controllers you can visit Zurich Instruments YouTube channel and watch the following video:
Manual Setup¶
In cases where the transfer function of the device under test (DUT) is unknown and only little noise couples into the system from the environment, a manual approach is often the quickest way to get going. For manual configuration of a new control loop it is recommended to start with a small value for P and set the other parameters (I, D, D Limit) to zero. By enabling the controller one will then immediately see if the sign of P is correct and if the feedback is acting on the correct output parameter. For instance, by checking the numbers (Error, Shift, Out) displayed in the PID / PLL tab. A stepwise increase of the integral gain, I, will then help to zero the PID error signal completely. Enabling the derivative gain, D, can increase the speed of the feedback loop, but it can also cause an instable feedback loop behavior which sometimes can be mitigated by activating the associated low-pass filter.
Functional Elements¶
| Control/Tool | Option/Range | Description |
|---|---|---|
| Enable | ON / OFF | Enable the PID controller |
| Mode | Operation mode of the PID module. | |
| PID | The PID is used for a general application. | |
| PLL | The PID is used to control an internal oscillator. | |
| ExtRef | The PID is used by the external reference to control an internal oscillator. | |
| Auto Mode | This defines the type of automatic adaptation of parameters in the PID. | |
| Off | No automatic adaptation. | |
| PID Coeff | The coefficients of the PID controller are automatically set. | |
| Coeff + BW (low) | The PID coefficients, the filter bandwidth and the output limits are automatically set using a low bandwidth. | |
| Coeff + BW (high) | The PID coefficients, the filter bandwidth and the output limits are automatically set using a high bandwidth. | |
| Adaptive | All parameters of the PID including the center frequency are adapted. | |
| Input | Select input source of PID controller | |
| Demodulator X | Demodulator cartesian X component | |
| Demodulator Y | Demodulator cartesian Y component | |
| Demodulator R | Demodulator magnitude component | |
| Demodulator Theta | Demodulator phase | |
| Input Channel | index | Select input channel of PID controller. |
| Setpoint | numeric value | PID controller setpoint |
| Phase Unwrap | ON / OFF | Enables the phase unwrapping to track phase errors past the +/-180 degree boundary and increase PLL bandwidth. |
| Filter BW | numeric value | Bandwidth of the demodulator filter used as an input. |
| Filter Order | Selects the filter roll off between 6 dB/oct and 48 dB/oct of the current demodulator. | |
| 1 | 1st order filter 6 dB/oct | |
| 2 | 2nd order filter 12 dB/oct | |
| 3 | 3rd order filter 18 dB/oct | |
| 4 | 4th order filter 24 dB/oct | |
| Harmonic | 1 to 1023 | Multiplier of the for the reference frequency of the current demodulator. |
| Output | Select output of the PID controller | |
| Sig Out 1 Amplitude | Feedback to the main signal output amplitude 1 | |
| Sig Out 2 Amplitude | Feedback to the main signal output amplitude 2 | |
| Oscillator Frequency | Feedback to any of the internal oscillator frequencies | |
| Output Channel | index | Select output channel of PID controller. |
| Center | numeric value | After adding the Center value to the PID output, the signal is clamped to Center + Lower Limit and Center + Upper Limit. |
| Lower Limit | numeric value | After adding the Center value to the PID output, the signal is clamped between Center - Lower Limit, and Center + Upper Limit. |
| Upper Limit | numeric value | After adding the Center value to the PID output, the signal is clamped between Center - Lower Limit, and Center + Upper Limit. |
| P (Hz/deg) | numeric value | PID proportional gain P |
| I (Hz/deg/s) | numeric value | PID integral gain I |
| D (Hz/deg*s) | numeric value | PID derivative gain D |
| D Limit TC/BW 3 dB | The cutoff of the low-pass filter for the D limitation, shown as either the filter time constant or the 3 dB cutoff frequency, depending on the selected TC mode. When set to 0, the low-pass filter is disabled. | |
| Rate | PID sampling rate and update rate of PID outputs. Needs to be set substantially higher than the targeted loop filter bandwidth. The numerical precision of the controller is influenced by the loop filter sampling rate. If the target bandwidth is below 1 kHz is starts to make sense to adjust this rate to a value of about 100 to 500 times the target bandwidth. If the rate is set too high for low bandwidth applications, integration inaccuracies can lead to non linear behavior. |
|
| Error | numeric value | Error = Set point - PID Input |
| Lock LED | grey/green | Indicates when the PID (configured as PLL) is locked. The PLL error is sampled at 5 Sa/s and its absolute value is calculated. If the result is smaller than 5 degrees the loop is considered locked. Only works if mode is PLL or ExtRef. |
| Shift | numeric value | Difference between the current output value Out and the Center. Shift = P*Error + I*Int(Error, dt) + D*dError/dt |
| Value | numeric value | Current output value |
| To Advisor |  |
Copy the current PID settings to the PID Advisor. |