DigiPid Help

Help for DigiPID
Version 2017-11-10

Overview

The webpage is in four sections: at the top are the operating parameters, in the middle is the setup (which probably never change once set), below that is a graph with a snapshot of current conditions, at the very bottom is a place to upload an output transfer curve.

In the middle (setup section), select which mode the unit is for: DC to run a external AOM driver or a laser driver, or RF for an external AOM amplifier. If RF output, set the VCO frequency. Select the VCO with the narrowest range which can work at the desired frequency.

Although possibly unclear, in Run box, the Target box shows as a voltage. Similarly, the graph showing output in RF output mode will show as voltage. IN DC output, these are obvious, voltage is voltage. In RF output it is less clear. The internal RF modulator runs between ±7.25V, approximately, where -7.25V is zero RF output and +7.25V is 100% RF output.

Webpage
Web ver		HTML, JS and CSS version
Embedded		Left: embedded, right: HDL
Saves		Number of times configuration was saved (max 20,000)
Configure - Monitor		Monitor:Shows current state
Configure - Monitor		Configure: Client changes parameters, must click Apply to implement
Apply		Appears in Configure, click to implement as shown
Save as default		If checked, will save as default power-up state, otherwise lost if unit is rebooted
Green/Red Circle		Green means connected to unit, red disconnected. Number shows how many clients currently connected
Run	P gain	Proprotional gain, normalized to 100%
	I gain	Integral gain, normalized to 100%
	D gain	Derivative gain, normalized to 100%
	Target	The voltage which the whole system is trying to maintain
	Currently	The current output level
Manual		When Manual mode is selected, the output level, can also adjust on the unit directly
Stop		When Stop mode is selected, the output level
Pulse¹	Frequency	When Pulse mode is selected, the frequency of the pulse output
Pulse¹	Duty cycle	When Pulse mode is selected, the duty cycle of the pulse output
Saturation	Input	When lit, indicates an analog input saturation, reduce analog gain
	Output	When lit, indicates an output saturation, reduce main gain
	Integrator	When lit, indicates error integrator saturation, reduce I gain
Input Parameters	Gain	Analog input gain, increase until input saturates then reduce gain
	Bandwidth	Analog input bandwidth, also affects the processing rate (2.5 times oversampled)
	Resistance	Analog input resistance, with 50Ω do not exceed 3V_rms for >1 second
Output Mode	DC	The DC output is active, all applicable parameters are in V (RF output is disabled)
Output Mode	RF	The RF output is active, all applicable parameters are normalized in % (DC output is still active)
DC Output Limits	Max	DC output only, the highest output voltage allowed, can be +ve or -ve but must be more positive than Min
DC Output Limits	Min	DC output only, the lowest output voltage allowed, can be +ve or -ve but must be more negative than Max
RF Frequency	Set	The target frequency for the RF output, when Active Lock selected
	Meas.	The measured RF output frequency
	Control	The control for the RF frequency. Manually set when Manually Set selected
	Lock?²	Either Actively Lock to find and keep the Target frequency
Chart	None	No chart
	Output	A snapshot of the current output, analog DC or RF level as applicable
	Input	A snapshot of the current analog input
	Transfer³	The output transfer curve in use
Output Transfer Curve³	Choose File⁴	Select the ASCII text file defining the output transfer curve
Output Transfer Curve³	Force Linear	Check to revert to a linear output transfer curve

Note 1: In DC output, the pulse output swings between DC Output Min and Max, in RF output between 0% and 100%
Note 2: When Active Lock, the RF frequency will constantly adjust slightly up and down around the Target frequency
Note 3: See the section on the Output Transfer Curve for details

Output Transfer Curve File

The output transfer curve defines the relationship between the calculated output and the actual output. It is only applicable in Run mode but applys to both DC and RF outputs. Use this to linearize a nonlinear element such as a RF or optical modulator. For example, if a modulator has a low response at low levels then the transfer curve can be used to bump up the output at those low levels. A linear output transfer curve gives a 1:1 calculated to output relationship: e.g. double the calculated output level gives double the actual output level. A nonlinear curve must be defined by a text file. The file rules are:

Any rule violation will invalidate the whole file.
Test for a valid file by including two coniguous wildly anomolous point and have the Chart show Output Transfer Curve to confirm, then fix those points. Two points are required because only 78% of the points are shown (800/1024 = 0.78).
Each point is "<calculated output><space><new output>;", note the mandatory space and the semi-colon delimiter.
Each pair can be on a new line or not, leading spaces ignored.
More than one space and/or tab are allowed.
Pairs can be each on their own line or many on one line, although the former is more legible.
Integers only, plain old ASCII, probably a .txt file.
Each pair has a calculated point ("Point") in the curve, a space, then the new output ("Output") value at that Point.
The Point is 0 to 1023 to cover the ±10V calculated range, where 0 = -10V, 511 = 0V and 1023 = +10V.
The Output value is 0 to 65535 to cover the ±10V range, where 0 = -10V, 32767 = 0V and 65535 = +10V.
Note that both the Point and Output are limited by the DC Output Min and Max when in DC output mode, and ±7.25V when in RF output mode.
Note than Points and Outputs outside of the above limits are harmless and not used.
The default end points are "0 0;" and "1023 65535;", may be overwritten if you wish.
Example: to have a calculated 0.000V actually output +0.100V, the pair is "511 33095;".
Pairs must be in order, specifically the Points must be increasing.
Gaps in missing points are interpolated (this is the usual case where not all 1024 points are defined).
Although negative slopes in the new outputs are allowed, they can be trouble for stability.

Following is the contents of a short sample file which has several discontinuities defined. Note that although "0 0;" is defined, it is implied and not necessary. The last line overrides the default "1023 65535;".

0 0;
512 32768;
750 50000;
1023 65000;