PHD2 NINA meridan flip issue

[Xavier Peillon]

PHD2 DEC Guiding Failure After Meridian Flip (EQ6-R + GSS + NINA)

Hello,

I am trying to diagnose a reproducible guiding issue that occurs after every meridian flip.

Equipment Mount

• SkyWatcher EQ6-R
• GS Server (GSS) 1.1.0.2
• ASCOM GS Sky Telescope driver
• Pulse guiding via ASCOM (no ST4)

Software

• NINA 3.2
• PHD2 2.6.14
• GS Server 1.1.0.2

Guide Scope

• SkyWatcher Evoguide 50ED
• Focal length: 242 mm

Guide Camera

• ZWO ASI120MM Mini
• Pixel size: 3.75 µm
• Binning 1x1

---

PHD2 Settings

• Calibration step: 750 ms (recommended by PHD2 calibration calculator)
• Guide speed: 0.9x sidereal
• Auto-restore calibration: OFF
• Reverse DEC output after meridian flip: OFF
• Use DEC compensation: ON
• Multi-star guiding: ON

Calibration is performed successfully and guiding quality is excellent.

---

NINA Settings

I use the Advanced Sequencer.

The sequence contains:

• Start Guiding
• Force Calibration = ON

Meridian flips are handled by the native NINA Meridian Flip Trigger.

---

Problem Description

A fresh calibration always works perfectly.

Typical sequence:

Fresh calibration
→ Guiding starts
→ Excellent guiding
→ Imaging runs normally

However, after a meridian flip:

Meridian Flip
→ Guiding resumes
→ DEC immediately diverges
→ DEC corrections saturate (~2500 ms)
→ Guide star eventually lost

RA remains normal.

The problem is only on the DEC axis.

---

Very Important Observation

If I stop guiding and perform a new calibration manually:

New calibration
→ Guiding becomes perfect immediately

The rest of the night runs normally.

Therefore:

• Fresh calibration = always good
• Reused/transformed calibration after side-of-pier change = always bad

This behaviour is 100% reproducible.

---

What I Have Verified Side of Pier

GSS reports SideOfPier correctly.

In NINA:

Side of Pier = East / West

changes correctly.

In GSS:

pierEast / pierWest

also changes correctly.

Therefore GSS appears to provide SideOfPier information properly.

Calibration

Fresh calibrations are always successful.

Guiding

Excellent guiding before the flip.

Auto-Restore

Disabled.

PHD2 logs confirm:

AutoLoadCalibration = 0

---

What Makes Me Suspicious

I suspect that NINA does not actually execute a new calibration after the meridian flip.

At the beginning of the night I can see:

Calibration Begins
Calibration Complete
Guiding Begins

After the meridian flip I only see:

Guiding Begins

and no new calibration.

It looks like the Meridian Flip Trigger restarts guiding directly instead of executing my "Start Guiding → Force Calibration" instruction.

---

Additional Information

• Guiding is done through ASCOM pulse guiding.
• No ST4 cable is used.
• GSS correctly reports SideOfPier.
• EQ6-R performs the physical meridian flip correctly.
• NINA recenters successfully after the flip.
• Only DEC guiding fails after the flip.
• A manual recalibration immediately fixes the problem.

---

Questions

1. Has anyone seen PHD2 fail to reuse a calibration after a side-of-pier change while a fresh calibration works perfectly?
2. Does the NINA Meridian Flip Trigger bypass the "Force Calibration" option of the Start Guiding instruction? I know i shoudn't ask for force calibration after meridian but the problem doesn't change if i use invert dec after meridan button or not...
3. Is there any known issue involving:
   • EQ6-R
   • GS Server (GSS)
   • PHD2
   • Meridian Flip
   • DEC guiding failure after flip

Any advice would be greatly appreciated.

[Brian Valente]

Xavier:

Please send your logs: https://openphdguiding.org/getting-help/

Many people use meridian flip and NINA without issue. I don't know why you are recalibrating after a flip, that isn't necessary. If your Dec is going on the opposite direction, your settings for reverse Dec need to be changed. use the calibrate meridian flip tool to assist you here.

We can't really offer much meaningful feedback until we see your logs. 

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Brian 

Brian Valente

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[steve]

Hi
GSS, so reverse DEC after the flip:

HTH and CS
Steve

[Brian Valente]

yes, that's the feature. You can use the calibrate meridian flip to determine the correct setting, or just flip the setting and see how it goes.

Beyond that, we would need to see the logs if you have followup questions.

Brian

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/1e423103-bbf6-4b01-b107-f1ae460b86df%40gmail.com.

[Xavier Peillon]

Hi, 

Thanks for the reply.

Here is the log of my latest night.

I didn't even see there was a calibrate meridian flip option... Shame on me. I will try this next night. 

Hope it will allow something new, even if i already tried meridian flip with & without the Dec invert option without any difference...

The only thing i didn't tried yet is the option "stop guiding while mount is moving"...

Xav

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[Brian Valente]

Xavier

Although you didn't ask about this, your primary period RA is very high, and is likely limiting your guiding/tracking results. the residual error is 0.90" so you won't get below that in RA RMS, and your RA is currently about 2x Dec.

Consider using PPEC algorithm for RA with the period set to 477 seconds, disable auto adjust period, and set the aggression to 80 for both predictive and reactive.

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAHaFNjxuoXf_5UoZDqfLQbiogo_SACcWaeY_VgJw1Q0TSa-ZaA%40mail.gmail.com.

[Brian Valente]

sorry - here's the complete graph

[Brian Valente]

Xavier

>>>Here is the log of my latest night.

please follow the directions below and use the built-in PHD Log Upload feature as described here to send all the relevant logs: 

https://openphdguiding.org/getting-help/ 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAHaFNjxuoXf_5UoZDqfLQbiogo_SACcWaeY_VgJw1Q0TSa-ZaA%40mail.gmail.com.