Rotator terminology and understanding their motions

I’m using a PlaneWave IRF90 on one of their L-mounts, and it’s been great for tracking in the alt-az configuration. PlaneWave has recently integrated their main instrument control packages into a single PWI4 suite. I’m still controlling the rotator with their previous PWI3 version. They have no documentation for their current version of PWI3.

There’s an interplay between the straight, raw mechanical angle of the rotator as delivered by the encoders, something labeled as “position angle,” and something else that pops up during various operations called “field angle.” Our observing program would go more smoothly if we had better control of our image orientation. We’re new to the alt-az-rotator way of doing things.

At this point, I’m mostly interested in keeping track of the encoder angle. Given that “position angle” can apparently be set, but “field angle” cannot (as near as I can tell), the conclusion might be that field angle is the indicator that retains the encoder angle. But, the appearance of “field angle” in the control panel is transient. In the manual I have in hand, it gives the impression that the encoder angle is retained in the “position angle” display until the “field angle” display has been activated by an operational change.

I’ll be back in the dome in a few days to study rotator and control software responses to test out some of these ideas. Anyone having the knowledge to control a rotator to the point where they could use one to actually measure a position angle (not our objective, but indicative of a level of understanding), I’d be grateful for a response.

Does this help?
https://www2.keck.hawaii.edu/inst/KSDs/40/html/ksd40-55.14.html

or this?
Position angle - Wikipedia(usually,direction%20of%20the%20right%20ascension.
Ray

Thank you for taking the time to respond Ray.

The Keck document is great, but doesn’t translate well to the PlaneWave implementation of their rotator control software.

Position angle per se is not the issue. That’s a “simple” measurement. I first encountered it in the 1980s working with Georgia State’s CHARA, where they were using speckle interferometry, with assistance from Charles Worley of USNO (a visual binary guy using his filar micrometer to obtain separations and position angles) to determine stellar orbits.

PlaneWave has been uncharacteristically silent this last month. They’ve always been great in supporting their instrumentation. Perhaps they’re busy manning a booth at the AAVSO conference.

Anyway, I’ve simply been hoping that someone has the “Ah Hah!” piece of information that will save me the time of studying the rotator and control software on their own terms. I’d rather be doing something else, but it takes what it takes, right?

Thanks again Ray. All the best. Tom