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.

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.

Figure 2: PID controller block diagram

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¶

Table 2: PID tab: PID section
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	numeric value	PID proportional gain P
I	numeric value	PID integral gain I
D	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 = PError + IInt(Error, dt) + D*dError/dt
Value	numeric value	Current output value
To Advisor		Copy the current PID settings to the PID Advisor.
Rate (Sa/s)		Defines the PID sampling rate, the number of samples that are sent to the host computer per second. A rate of about 7-10 higher as compared to the filter bandwidth usually provides sufficient aliasing suppression. This is also the rate of data received by LabOne Data Server and saved to the computer hard disk. This setting has no impact on the sample rate on the auxiliary outputs connectors. Note: the value inserted by the user may be approximated to the nearest value supported by the instrument.
Enable PID Streaming	ON / OFF	Enables the data acquisition and streaming of PID samples to the host computer for the corresponding PID. The corresponding PID controller should be enabled first. The streaming rate is defined in the field on the right-hand side. Enabling a stream activates a corresponding element in the numeric tab and allows for PID samples to be visualized and analyzed in any of the LabOne measurement tools. Note: enabling a PID's data transfer increases the load on the physical connection to the host computer.
Trigger Source		Select the source of trigger signal for the acquisition of PID samples.
	Trigger Input 1	Source of trigger signal is Trigger Input 1 on the instrument's front panel.
	Trigger Input 2	Source of trigger signal is Trigger Input 2 on the instrument's front panel.
	Trigger Input 3	Source of trigger signal is Trigger Input 3 on the instrument's front panel.
	Trigger Input 4	Source of trigger signal is Trigger Input 4 on the instrument's front panel.
	Software Trigger	Source of trigger signal is generated internally and can be controlled using the node "/dev..../system/swtriggers/0/single".
Trigger Mode		Select the starting point of the trigger event.
	None	Please update device firmware to enable HW Trigger functionality.
	Rise	Trigger events start at the rising edge of the trigger signal.
	Fall	Trigger events start at the falling edge of the trigger signal.
	Both	Trigger events start at rising and falling edges of the trigger signal.
Burst Length		Number of PID samples to acquire for a single trigger event.
Enable Triggering		Once enabled, the PID samples are transferred to the host computer when a trigger event occurs. When disabled, the transfer of PID samples to the host computer is continuous. Note that for both cases the corresponding PID controller and its Data Transfer must be enabled.