What does the "Input Gain" setting do?

[Kyle Douglass]

Hi all,
I was just curious if anyone has played with the "Input Gain" setting in the Micro-Manager pgFocus plugin. Specifically, will decreasing this value prevent the stage from "hopping," i.e. jumping back and forth between two different but neighboring DAC levels?

The reason I ask is because some highly scattering samples return a distorted beam that's kind-of-Gaussian but not quite. We can sometimes lock onto this beam, but if it's distorted just enough then the pgFocus often makes slight errors in determining its centroid position; this results in the fast switching between neighboring DAC levels.

This situation is hard to reproduce in the lab, which is why I am asking here.

Cheers,
Kyle

[Karl Bellve]

Hi Kyle,

Input Gain is for calibrating the ADC due to the use of resistors to convert a ±10V ADC to a ±5V ADC via an Op Amp. Because resistors are never accurate, the gain via op amp is never 2 (incoming voltage * 2). Since resistors are linear at a specific temperature, we can just use a conversion factor and that is what that input gain is. It should be around 1. In practice, input gain probably doesn't matter. There are too many other errors in the system than to worry about 1-2% error in the input gain. 

The formula I use to determine input gain is on the wiki under the Analog to Digital Converter section: 

((2/10) * 2^14) / ((abs(-1 Volt) + (1 Volt)) = gain. 

For your issue, you could try and change the distance pgFocus moves to correct focus.

In the firmware code, the variable is dDriftCorrection and it is a percentage. I think it is 0.5 (or 50%). If you change it, I wouldn't go any higher than 80% otherwise you might get ringing. I never tested what happens if you go lower but going lower might solve your issue.

The command to change drift correction is "step". "step" without any value will print the value pgFocus is using. "step" with a value will change the value. I artificially limit the range to 0 > Value < 1.50,

Thanks for posting this question on the mailing list. 

PS. Some of the parts for your second pgFocus were on backorder, but I just got a notification that Mouser billed me, so I should be getting the parts soon.

Cheers 

Karl Bellvé

Biomedical Imaging Group
Molecular Medicine
University of Massachusetts Medical School

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[Kyle Douglass]

The command to change drift correction is "step". "step" without any value will print the value pgFocus is using. "step" with a value will change the value. I artificially limit the range to 0 > Value < 1.50,

Thanks for the detailed response, Karl. I'm not in the lab at the moment to check this. Is the "step" parameter accessible via Micro-Manager's Device Property Browser?

 

PS. Some of the parts for your second pgFocus were on backorder, but I just got a notification that Mouser billed me, so I should be getting the parts soon.

Sounds good to me :)

Kyle

[Karl Bellve]

On Tue, Feb 23, 2016 at 3:20 AM Kyle Douglass <kyle.m....@gmail.com> wrote:

The command to change drift correction is "step". "step" without any value will print the value pgFocus is using. "step" with a value will change the value. I artificially limit the range to 0 > Value < 1.50,

Thanks for the detailed response, Karl. I'm not in the lab at the moment to check this. Is the "step" parameter accessible via Micro-Manager's Device Property Browser?

Nope.

I can make it available the next time I am in the pgFocus plugin and Device Adapter code.