|
I have always used 0.8x as the guide rate when training PEC on my G11 with Gemini 1 Level 4.? I was just looking at the Gemini instructions in PEMPro V3 and it has this warning:? The Gemini firmware only supports 0.3x and 0.5x guide rates - 0.5x is recommended.? This conflicts with the description of command ID 502, Guide Speed used for training PEC, in the Gemini Level 4 Users Manual.? That seems to indicate the full 0.2x, 0.5x, and 0.8x range is valid.? Which is it?
|
Hi?sbasprez
you should be fine with up to 0.8x, although 0.5x is definitely recommended
Where did you see this error? I am in PEMPro now (and have used it for years) and never ran across that error message, regardless of what guide rate i put in
Brian
I have always used 0.8x as the guide rate when training PEC on my G11 with Gemini 1 Level 4.? I was just looking at the Gemini instructions in PEMPro V3 and it has this warning:? The Gemini firmware only supports 0.3x and 0.5x guide rates - 0.5x is recommended.? This conflicts with the description of command ID 502, Guide Speed used for training PEC, in the Gemini Level 4 Users Manual.? That seems to indicate the full 0.2x, 0.5x, and 0.8x range is valid.? Which is it?
-- Brian?
Brian Valente portfolio
|
Update:
i found that reference in the documentation.
i checked with Ray, i think that may be out of date. the valid range is 0.2x - 0.8x
however, I really recommend you stick with 0.5x for two reasons
1. it's the best balance between slower speed (better for PEC) and faster speed (better for guiding)
2. there may be some parts of the code that are hard-coded to 0.5x. i don't know this for sure, i've only heard this in passing, so it may not be true. So the recommendation is 0.5x
also FYI if you change your guidespeed at any time, you will need to redo your PEC to match the guidespeed
Brian
I have always used 0.8x as the guide rate when training PEC on my G11 with Gemini 1 Level 4.? I was just looking at the Gemini instructions in PEMPro V3 and it has this warning:? The Gemini firmware only supports 0.3x and 0.5x guide rates - 0.5x is recommended.? This conflicts with the description of command ID 502, Guide Speed used for training PEC, in the Gemini Level 4 Users Manual.? That seems to indicate the full 0.2x, 0.5x, and 0.8x range is valid.? Which is it?
-- Brian?
Brian Valente portfolio
|
I always learn something new on this forum. I presently avoid needing PEC by the few improvements I made to the RA drive. That hot PE down to the 1 arcsec RMS (~2.4 arcsec Peak to Peak) range, typical of my area's seeing.? I do use autoguiding at 0.5x Sidereal rate to correct other errors like polar alignment error/drift.??
Earlier, I did use the Gemini-1 built in PEC training and built in PEC averaging .? It worked fine.??
However, from this thread, I really don't understand why the autoguide rate has anything at all to do with PEC training.? The autoguider is turned off during PEC data acquisition.? The "autoguide" camera is only used to "watch" the tracked star's RA position during sidereal tracking.? You could even be tracking the star with 2 or 3 second exposures.??
The PEC is fitted to the recorded unguided tracking data later, by either the Gemini built in software or the external PC software.??
So...can someone explain why "autoguide rate" has something to do with PEC??
Thanks, Michael
On Mon, Aug 17, 2020, 12:24 PM Brian Valente < bvalente@...> wrote: Update:
i found that reference in the documentation.
i checked with Ray, i think that may be out of date. the valid range is 0.2x - 0.8x
however, I really recommend you stick with 0.5x for two reasons
1. it's the best balance between slower speed (better for PEC) and faster speed (better for guiding)
2. there may be some parts of the code that are hard-coded to 0.5x. i don't know this for sure, i've only heard this in passing, so it may not be true. So the recommendation is 0.5x
also FYI if you change your guidespeed at any time, you will need to redo your PEC to match the guidespeed
Brian
I have always used 0.8x as the guide rate when training PEC on my G11 with Gemini 1 Level 4.? I was just looking at the Gemini instructions in PEMPro V3 and it has this warning:? The Gemini firmware only supports 0.3x and 0.5x guide rates - 0.5x is recommended.? This conflicts with the description of command ID 502, Guide Speed used for training PEC, in the Gemini Level 4 Users Manual.? That seems to indicate the full 0.2x, 0.5x, and 0.8x range is valid.? Which is it?
--
Brian?
Brian Valente portfolio
|
On Mon, Aug 17, 2020 at 04:39 PM, Michael Herman wrote:
So...can someone explain why "autoguide rate" has something to do with PEC??
Hi Michael, Recording PE data doesn't require knowing the guide rate. Programming PEC data into Gemini - does. If you are programming PEC manually (using HC or autoguider corrections) then the corrections recorded are relative to the guide rate. If you change the guide rate, the correction rates will also need to be adjusted during PEC playback, and Gemini doesn't do this automatically. So, whatever rate you recorded and programmed PEC is the rate you should use for PEC playback. When PEC is programmed from the PC, say using PemPro, the corrections are also sent as the number of pulses needed for each of the corrections. This is also based on the guiding speed: if the speed is higher, then fewer pulses are needed, if lower -- more pulses. If the guiding speed is changed after the programming, the number of pulses of corrections will no longer be right and the corrections will be either faster or slower than what was programmed. Regards, ? ?-Paul
|
Hi Michael
Rene is the best person to answer this, but here are a few tidbits of my understanding
When you record PEC using a third party tool like PEMPro, the guide rate affects the speed at which corrections are applied (i'm not sure if it's in the capture, the playback, or both). First part is when you gather the data and then upload to the mount, Gemini needs to be at the same guide rate.?
Then when you're guiding, the guide rate needs to be at the same value as well. if you decide you want to guide at a different rate, you need to disable PEC or re-do it at the new rate. ?
for built-in PEC training, i'm not sure how much the above applies
On Mon, Aug 17, 2020 at 1:39 PM Michael Herman < mherman346@...> wrote: I always learn something new on this forum. I presently avoid needing PEC by the few improvements I made to the RA drive. That hot PE down to the 1 arcsec RMS (~2.4 arcsec Peak to Peak) range, typical of my area's seeing.? I do use autoguiding at 0.5x Sidereal rate to correct other errors like polar alignment error/drift.??
Earlier, I did use the Gemini-1 built in PEC training and built in PEC averaging .? It worked fine.??
However, from this thread, I really don't understand why the autoguide rate has anything at all to do with PEC training.? The autoguider is turned off during PEC data acquisition.? The "autoguide" camera is only used to "watch" the tracked star's RA position during sidereal tracking.? You could even be tracking the star with 2 or 3 second exposures.??
The PEC is fitted to the recorded unguided tracking data later, by either the Gemini built in software or the external PC software.??
So...can someone explain why "autoguide rate" has something to do with PEC??
Thanks, Michael
On Mon, Aug 17, 2020, 12:24 PM Brian Valente < bvalente@...> wrote: Update:
i found that reference in the documentation.
i checked with Ray, i think that may be out of date. the valid range is 0.2x - 0.8x
however, I really recommend you stick with 0.5x for two reasons
1. it's the best balance between slower speed (better for PEC) and faster speed (better for guiding)
2. there may be some parts of the code that are hard-coded to 0.5x. i don't know this for sure, i've only heard this in passing, so it may not be true. So the recommendation is 0.5x
also FYI if you change your guidespeed at any time, you will need to redo your PEC to match the guidespeed
Brian
I have always used 0.8x as the guide rate when training PEC on my G11 with Gemini 1 Level 4.? I was just looking at the Gemini instructions in PEMPro V3 and it has this warning:? The Gemini firmware only supports 0.3x and 0.5x guide rates - 0.5x is recommended.? This conflicts with the description of command ID 502, Guide Speed used for training PEC, in the Gemini Level 4 Users Manual.? That seems to indicate the full 0.2x, 0.5x, and 0.8x range is valid.? Which is it?
--
Brian?
Brian Valente portfolio
-- Brian?
Brian Valente portfolio
|
UPDATE: The 0.3x and 0.5x from the documentation are incorrect - those are values from the 492 controller, not the Gemini.
Brian
On Mon, Aug 17, 2020 at 2:00 PM Paul Kanevsky < yh@...> wrote: On Mon, Aug 17, 2020 at 04:39 PM, Michael Herman wrote:
So...can someone explain why "autoguide rate" has something to do with PEC??
Hi Michael,
Recording PE data doesn't require knowing the guide rate. Programming PEC data into Gemini - does.
If you are programming PEC manually (using HC or autoguider corrections) then the corrections recorded are relative to the guide rate. If you change the guide rate, the correction rates will also need to be adjusted during PEC playback, and Gemini doesn't do this automatically. So, whatever rate you recorded and programmed PEC is the rate you should use for PEC playback.
When PEC is programmed from the PC, say using PemPro, the corrections are also sent as the number of pulses needed for each of the corrections. This is also based on the guiding speed: if the speed is higher, then fewer pulses are needed, if lower -- more pulses. If the guiding speed is changed after the programming, the number of pulses of corrections will no longer be right and the corrections will be either faster or slower than what was programmed.
Regards,
? ?-Paul
-- Brian?
Brian Valente portfolio
|
Thank you for those answers.
I think Paul's ideas might be close to the mark.? I still don't quite "see" the issue in my mind's eye yet. I think now that the autoguide speed really applies to using PEC and Autoguiding actively AFTER the PEC curve has been generated.? The autoguide speed has zero to do with taking the PE data.? It can't because the video camera is just capturing the target star location in its image plane.? No autoguiding pulses are used at all in taking that tracking data.
So the?autoguide speed recommendation must have to do after, with PEC turned on.? Then I can see how the?autoguide rate might come into play.??
However, if the corrections needed to be very fast, say for a very sharp worm or coupler induced error, the faster your autoguide rate that is "allowed" by Gemini would be able to counteract such severe trouble.? However, in my PEC experience, you want to "smooth out" any sharp impulses. That is why the Gemini-1 provides for you to run multiple PE runs, so the software can just average out the corrections.? You do not want to be "chasing the seeing" as the saying goes.??
If you?look at the PEC curves that typically go from -2 arcsec to?+ 2 arcsec over a worm period (4 minutes on G11) you would not need a very fast autoguide speed, so limiting that to 0.5 sidereal is sensible.? Anyway it will also matter if your FL is very high...so you are more sensitive to star movement.? At that point you might want to allow the autoguider to move the mount faster, at 0.8 of sidereal maybe.??
It's all one big experiment for us observers.
Have fun, stay well, and (the lastest issue:thunderstorms!)?hope your power stays on!
Michael
On Mon, Aug 17, 2020 at 2:44 PM Brian Valente < bvalente@...> wrote: UPDATE: The 0.3x and 0.5x from the documentation are incorrect - those are values from the 492 controller, not the Gemini.
Brian
On Mon, Aug 17, 2020 at 2:00 PM Paul Kanevsky < yh@...> wrote: On Mon, Aug 17, 2020 at 04:39 PM, Michael Herman wrote:
So...can someone explain why "autoguide rate" has something to do with PEC??
Hi Michael,
Recording PE data doesn't require knowing the guide rate. Programming PEC data into Gemini - does.
If you are programming PEC manually (using HC or autoguider corrections) then the corrections recorded are relative to the guide rate. If you change the guide rate, the correction rates will also need to be adjusted during PEC playback, and Gemini doesn't do this automatically. So, whatever rate you recorded and programmed PEC is the rate you should use for PEC playback.
When PEC is programmed from the PC, say using PemPro, the corrections are also sent as the number of pulses needed for each of the corrections. This is also based on the guiding speed: if the speed is higher, then fewer pulses are needed, if lower -- more pulses. If the guiding speed is changed after the programming, the number of pulses of corrections will no longer be right and the corrections will be either faster or slower than what was programmed.
Regards,
? ?-Paul
--
Brian?
Brian Valente portfolio
|
I think Paul's ideas might be close to the mark. I still don't quite "see" the issue in my mind's eye yet.
I think now that the autoguide speed really applies to using PEC and Autoguiding actively AFTER the PEC curve has
been generated. The autoguide speed has zero to do with taking the PE data. It can't because the video camera is
just capturing the target star location in its image plane. No autoguiding pulses are used at all in taking that tracking
data. That's incorrect if you are using an autoguider to program PEC data. The autoguider keeps the star centered so it MUST send pulse guide commands via the ASCOM interface. The Gemini moves the mount and keeps track of the movement at that autoguider rate. What gets stored are indicators to move forward or backward (at autoguider speed) at each internal clock "tick". Gemini PEC data is recorded based on the autoguide speed. If you change the autoguide speed after collecting periodic error playback will be either under or over-emphasized. Also, when recording and averaging multiple cycles via an autoguider there are other problems besides seeing. You are also inherently introducing phase error from camera delay as well as potential periodic error from uncorrectable frequencies (like the 3.15x frequency). This will lead to an inferior PEC curve, even when averaged. BTW, that was my mistake reducing the autoguider rates to just two options (0.3x and 0.5x). I'll restore the full range in the next PEMPro build. -Ray Gralak Author of APCC (Astro-Physics Command Center): Author of PEMPro V3: Author of Astro-Physics V2 ASCOM Driver: -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Michael Herman
Sent: Monday, August 17, 2020 4:06 PM
To: [email protected]
Subject: Re: [Losmandy_users_io] Valid Guide Rates for PEC on Gemini Level 4
Thank you for those answers.
I think Paul's ideas might be close to the mark. I still don't quite "see" the issue in my mind's eye yet.
I think now that the autoguide speed really applies to using PEC and Autoguiding actively AFTER the PEC
curve has been generated. The autoguide speed has zero to do with taking the PE data. It can't because the
video camera is just capturing the target star location in its image plane. No autoguiding pulses are used at all
in taking that tracking data.
So the autoguide speed recommendation must have to do after, with PEC turned on. Then I can see how the
autoguide rate might come into play.
However, if the corrections needed to be very fast, say for a very sharp worm or coupler induced error, the
faster your autoguide rate that is "allowed" by Gemini would be able to counteract such severe trouble.
However, in my PEC experience, you want to "smooth out" any sharp impulses. That is why the Gemini-1
provides for you to run multiple PE runs, so the software can just average out the corrections. You do not want
to be "chasing the seeing" as the saying goes.
If you look at the PEC curves that typically go from -2 arcsec to + 2 arcsec over a worm period (4 minutes on
G11) you would not need a very fast autoguide speed, so limiting that to 0.5 sidereal is sensible. Anyway it will
also matter if your FL is very high...so you are more sensitive to star movement. At that point you might want
to allow the autoguider to move the mount faster, at 0.8 of sidereal maybe.
It's all one big experiment for us observers.
Have fun, stay well, and (the lastest issue:thunderstorms!) hope your power stays on!
Michael
On Mon, Aug 17, 2020 at 2:44 PM Brian Valente <bvalente@...> wrote:
UPDATE:
The 0.3x and 0.5x from the documentation are incorrect - those are values from the 492 controller, not
the Gemini.
Brian
On Mon, Aug 17, 2020 at 2:00 PM Paul Kanevsky <yh@...> wrote:
On Mon, Aug 17, 2020 at 04:39 PM, Michael Herman wrote:
So...can someone explain why "autoguide rate" has something to do with PEC?
Hi Michael,
Recording PE data doesn't require knowing the guide rate. Programming PEC data into Gemini -
does.
If you are programming PEC manually (using HC or autoguider corrections) then the corrections
recorded are relative to the guide rate. If you change the guide rate, the correction rates will also need to be
adjusted during PEC playback, and Gemini doesn't do this automatically. So, whatever rate you recorded and
programmed PEC is the rate you should use for PEC playback.
When PEC is programmed from the PC, say using PemPro, the corrections are also sent as the
number of pulses needed for each of the corrections. This is also based on the guiding speed: if the speed is
higher, then fewer pulses are needed, if lower -- more pulses. If the guiding speed is changed after the
programming, the number of pulses of corrections will no longer be right and the corrections will be either faster
or slower than what was programmed.
Regards,
-Paul
--
Brian
Brian Valente
portfolio brianvalentephotography.com <>
--
Michael Herman
mobile: 408 421-1239
email: mherman346@...
|
On Mon, Aug 17, 2020 at 08:23 PM, Ray Gralak wrote:
That's incorrect if you are using an autoguider to program PEC data. The autoguider keeps the star centered so it MUST send pulse guide commands via the ASCOM interface. The Gemini moves the mount and keeps track of the movement at that autoguider rate. What gets stored are indicators to move forward or backward (at autoguider speed) at each internal clock "tick".
Gemini PEC data is recorded based on the autoguide speed. If you change the autoguide speed after collecting periodic error playback will be either under or over-emphasized.
Ray is exactly right. This is what I was trying to say, albeit a little less clearly :) Periodic error correction pulses are recorded and stored? at the current guide speed by Gemini, regardless of how PEC is programmed. If you change the guide rate later, the pulses will no longer match the speed and the result will be overshoots or undershoots by PEC. Both not desirable.
|
Good morning all,
Based on my observations using my G11 with Gemini 2 in the past few years, the guide rate does not affect PEC once a PEC file is loaded. The currPEC.pec file contains all the information required for PEC to run independently of the guide rate.
Also, note that serial command 502 always returns 0.5, regardless of the actual guide rate used to train PEC, so it cannot be used to determine the PEC rate; you have to look at the clock divisors in the currPEC.pec file to determine the PEC rate.
Attached is the first section of a draft document I am writing on guiding and PEC.
Eric
|
Eric, I recall our discussion on the CCDWare forum last year, where you didn't believe me that the PEC move distance was different between east and west moves. I am glad to see you now understand. :-) Based on my observations using my G11 with Gemini 2 in the past few years, the guide rate does not affect
PEC once a PEC file is loaded Yes, at mount boot time, the Gemini firmware reads the PEC data, and the PEC table is calculated/loaded. However, I don't think that changing the guide rate after booting recalculates the PEC table. If the Gemini firmware does not recalculate the PEC table there can be two effects at guide rates different from the guide rate at boot time: 1) Playback of the PEC data is not as effective (i.e., under or over-emphasized) 2) There may be RA drift, which might be why in your document you say you wrote: However, I have observed that when the PEC clock divisors and the current guide rate do not match,
while tracking at sidereal rate, the mount frequently reports its velocity as ¡°Slewing¡± as opposed
to ¡°Tracking¡±. This implies that despite the rate divisor values in the PEC table, the Gemini firmware is using the current guide rate instead of the rates defined by the divisors. -Ray Gralak Author of APCC (Astro-Physics Command Center): Author of PEMPro V3: Author of Astro-Physics V2 ASCOM Driver: -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Cyclone
Sent: Tuesday, August 18, 2020 5:37 AM
To: [email protected]
Subject: Re: [Losmandy_users_io] Valid Guide Rates for PEC on Gemini Level 4
Good morning all,
Based on my observations using my G11 with Gemini 2 in the past few years, the guide rate does not affect
PEC once a PEC file is loaded. The currPEC.pec file contains all the information required for PEC to run
independently of the guide rate.
Attached is the first section of a draft document I am writing on guiding and PEC.
Eric
|
>>>
Periodic error correction pulses are recorded and stored? at the current guide speed?by Gemini, regardless of how PEC is programmed
yep - glad you guys added some meat to that bone
On Tue, Aug 18, 2020 at 5:36 AM Paul Kanevsky < yh@...> wrote: On Mon, Aug 17, 2020 at 08:23 PM, Ray Gralak wrote:
That's incorrect if you are using an autoguider to program PEC data. The autoguider keeps the star centered so it MUST send pulse guide commands via the ASCOM interface. The Gemini moves the mount and keeps track of the movement at that autoguider rate. What gets stored are indicators to move forward or backward (at autoguider speed) at each internal clock "tick".
Gemini PEC data is recorded based on the autoguide speed. If you change the autoguide speed after collecting periodic error playback will be either under or over-emphasized.
Ray is exactly right. This is what I was trying to say, albeit a little less clearly :) Periodic error correction pulses are recorded and stored?at the current guide speed by Gemini, regardless of how PEC is programmed. If you change the guide rate later, the pulses will no longer match the speed and the result will be overshoots or undershoots by PEC. Both not desirable.
-- Brian?
Brian Valente portfolio
|
>>>
Also, note that serial command 502 always returns 0.5, regardless of the actual guide rate used to train PEC, so it cannot be used to determine the PEC rate; you have to look at the clock divisors in thew currPEC.pec file to determine the PEC rate.
this was the part i remembered about something in Gemini always returning 0.5x
[Edited Message Follows]
Good morning all,
Based on my observations using my G11 with Gemini 2 in the past few years, the guide rate does not affect PEC once a PEC file is loaded. The currPEC.pec file contains all the information required for PEC to run independently of the guide rate.
Also, note that serial command 502 always returns 0.5, regardless of the actual guide rate used to train PEC, so it cannot be used to determine the PEC rate; you have to look at the clock divisors in thew currPEC.pec file to determine the PEC rate.
Attached is the first section of a draft document I am writing on guiding and PEC.
Eric
-- Brian?
Brian Valente portfolio
|
Ray,
I still cannot get PEMPRO to work with my mount, but I wrote my own PEC programming software :)
You state "the Gemini firmware is using the current guide rate instead of the rates defined by the divisors". However, as I described in my previous post, this is not my observation. I can change the guide rate to any value, it does not change PEC behavior. The first time I noticed this is when I forgot to match the guide rate to the currPEC rate and collected residual PE data. The residual PE with PEC ON was well corrected regardless of the guide rate.
Do you have data that shows that the guide rate affects PEC? That behaviour does not match my mount.
Eric
|
I still cannot get PEMPRO to work with my mount, but I wrote my own PEC programming software :) PEMPro works well on other Gemini equipped mounts if you follow the directions. You seemed pretty stubborn about me being wrong about the move distances being different between East/West, so maybe you didn't follow the directions? You state "the Gemini firmware is using the current guide rate instead of the rates defined by the divisors".
However, as I described in my previous post, this is not my observation. I can change the guide rate to any
value, it does not change PEC behavior. You should get some correction when the rates are different, but not the best possible correction. The more severe effect is the extra drift introduced, which can cause poorer autoguiding RMS than if you turned PEC off. The first time I noticed this is when I forgot to match the guide rate to
the currPEC rate and collected residual PE data. The residual PE with PEC ON was well corrected regardless
of the guide rate. According to your PDF when you had mismatched guide and PEC rates you observed drift (mount would indicate "slew"). I've definitely seen logs where there has been extra drift when the rates do not match. I don't have a mount myself to test with but others can try this test. There is always the possibility that there has been a firmware change to account for this. Have you tried measuring drift with mismatched guide/pec rates? -Ray Gralak Author of APCC (Astro-Physics Command Center): Author of PEMPro V3: Author of Astro-Physics V2 ASCOM Driver: -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Cyclone
Sent: Tuesday, August 18, 2020 7:27 AM
To: [email protected]
Subject: Re: [Losmandy_users_io] Valid Guide Rates for PEC on Gemini Level 4
Ray,
I still cannot get PEMPRO to work with my mount, but I wrote my own PEC programming software :)
You state "the Gemini firmware is using the current guide rate instead of the rates defined by the divisors".
However, as I described in my previous post, this is not my observation. I can change the guide rate to any
value, it does not change PEC behavior. The first time I noticed this is when I forgot to match the guide rate to
the currPEC rate and collected residual PE data. The residual PE with PEC ON was well corrected regardless
of the guide rate.
Do you have data that shows that the guide rate affects PEC? That behaviour does not match my mount.
Eric
|
I still think it's a mis translation or a mis statement. I think the statement should be: ? ...the PEC data is recorded at the present Tracking speed....
It cannot be guide speed since there is no guiding being performed during PEC recording.? But Tracking rate surely would affect the PEC recording, since that determines the RA rate of speed and the corrections are matched to the worm rotation period.? ?
So in recording PEC data, I'd avoid using King rate, etc...just stick to Sidereal.??
Stay well, ...
Michael?
On Tue, Aug 18, 2020, 7:13 AM Brian Valente < bvalente@...> wrote: >>>
Periodic error correction pulses are recorded and stored? at the current guide speed?by Gemini, regardless of how PEC is programmed
yep - glad you guys added some meat to that bone
On Tue, Aug 18, 2020 at 5:36 AM Paul Kanevsky < yh@...> wrote: On Mon, Aug 17, 2020 at 08:23 PM, Ray Gralak wrote:
That's incorrect if you are using an autoguider to program PEC data. The autoguider keeps the star centered so it MUST send pulse guide commands via the ASCOM interface. The Gemini moves the mount and keeps track of the movement at that autoguider rate. What gets stored are indicators to move forward or backward (at autoguider speed) at each internal clock "tick".
Gemini PEC data is recorded based on the autoguide speed. If you change the autoguide speed after collecting periodic error playback will be either under or over-emphasized.
Ray is exactly right. This is what I was trying to say, albeit a little less clearly :) Periodic error correction pulses are recorded and stored?at the current guide speed by Gemini, regardless of how PEC is programmed. If you change the guide rate later, the pulses will no longer match the speed and the result will be overshoots or undershoots by PEC. Both not desirable.
--
Brian?
Brian Valente portfolio
|
Ray,
You seemed pretty stubborn about me being wrong about the move distances being different between East/West
The issue with PEMPRO is not the difference between East and West moves, but I don't want to get off topic.
According to your PDF when you had mismatched guide and PEC rates you observed drift.
The report does not say that. The mount reports its state as slewing periodically and momentarily, but there is no change in drift. I assume that because the PEC divisors are different than the guide divisors, the mount reports its state as slewing at each PEC correction, but there does not seem to be any other side effect.
Have you tried measuring drift with mismatched guide/pec rates?
I did measure the drift with the same PEC curve and different guide rates and the drift in RA does not change (approximately 1 arcsec/min). Hopefully someone else can measure their residual PE/drift at different guide rates using the same PEC curve so we have more than one sample. Eric
|
On Tue, Aug 18, 2020 at 11:20 AM, Michael Herman wrote:
I still think it's a mis translation or a mis statement.
I think the statement should be:
?
...the PEC data is recorded at the present Tracking speed....
Michael, there are two steps and you keep talking only about the first one. Step one is recording PE data, the other is programming it into Gemini. Recording data into Gemini requires knowing the guide rate, otherwise Gemini doesn't know the size of the corrections you are sending.
|
Eric, The issue with PEMPRO is not the difference between East and West moves, but I don't want to get off topic. At the time you were using PEMPro there was an issue introduced when adding the two-cyle PEC programming for the Gemini, but that has been long since fixed. Hopefully someone else can measure their residual PE/drift at different guide rates using the same PEC curve
so we have more than one sample. PEMPro has been able to program the Gemini controllers since 2005, so I've seen hundreds of curves where drift was introduced by using the wrong guide rate. Hopefully a few people will report if the amount of drift changes depending on guide rate. It could well be that the latest firmware has changed the behavior. That said, the amount of drift change when changing guide-rate will depend on the PEC curve. The lower the periodic error of the mount, the less drift will be introduced when changing guide rate. So, one arc-sec/minute could be right for your mount and a small change in guide rate. It could be a lot more under different circumstances. -Ray Gralak Author of APCC (Astro-Physics Command Center): Author of PEMPro V3: Author of Astro-Physics V2 ASCOM Driver: -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Cyclone
Sent: Tuesday, August 18, 2020 8:25 AM
To: [email protected]
Subject: Re: [Losmandy_users_io] Valid Guide Rates for PEC on Gemini Level 4
Ray,
You seemed pretty stubborn about me being wrong about the move distances being different between
East/West
The issue with PEMPRO is not the difference between East and West moves, but I don't want to get off topic.
According to your PDF when you had mismatched guide and PEC rates you observed drift.
The report does not say that. The mount reports its state as slewing periodically and momentarily, but there is
no change in drift. I assume that because the PEC divisors are different than the guide divisors, the mount
reports its state as slewing at each PEC correction, but there does not seem to be any other side effect.
Have you tried measuring drift with mismatched guide/pec rates?
I did measure the drift with the same PEC curve and different guide rates and the drift in RA does not change
(approximately 1 arcsec/min).
Hopefully someone else can measure their residual PE/drift at different guide rates using the same PEC curve
so we have more than one sample.
Eric
|
Michael Herman
Paul Kanevsky