So there are two types of drive systems that allow a telescope to track objects in the sky.  Objects in the sky rotate around the axis the earth rotates on.  

One uses two axis to track in altitude (angle the horizon), and azimuth (angle with respect to north).  This requires both axis to work in a coordinated motion to track an object with respect to time.

The second type of drive, has one axis (Right Ascension) aligned with the North Star (actually the north celestial pole) to track objects.  This axis rotates at a rate of 1 revolution per 24hrs.  The second axis of this system is the angle from the celestial equator.  So in this system every object has it's own set of coordinates.  Kind of like latitude and longitude.  To track and object all the telescope has to do is turn the right ascension axis at a constant rate.

In this second type of drive, to move from tracking one object to a new object, one must move both axis to the new coordinates.  With respect to the right ascension axis, as it moves from one coordinate to another, it will speed up (slew) and will keep track of the change in angle with respect to time.  

So my question is, can one with an S7-1200 have an axis turn at some constant speed while keeping track of it's angular position with respect with time?  Think of the angular position as time of day.  

Hello,

One uses two axis to track in altitude (angle the horizon), and azimuth (angle with respect to north).  This requires both axis to work in a coordinated motion to track an object with respect to time.

Siemens having solar tracking library which is based on altitude and latitude ( azimuth ) for S71200 and S7 1500 PLC. This will be useful for your application. Plz contact to your local Siemens Colleagues.

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FYI

https://w3.siemens.com/markets/global/en/machinebuilding/solar-production-machines/Documents/simply-follow-the-sun.pdf

http://w3.siemens.com/verticals/mea/en/solar-industry/field-supply/tracking-control/documents/e20001-a100-t112-x-7600.pdf

S7-1200 real time clock accuracy: +/- 60 secs/month