Re: [TASS] Tech Note 48

[Tom Droege <droege@WWA.COM>]

Peter and list since of general interest:


At 06:35 PM 9/2/99 +0100, you wrote:
>
>Tom, in tech note 48, there are a series of parameters for the Mark IV. Are
>these accurate?
>

We will no doubt run MPP mode with 80,000 or so (90,000?) full well
electrons.  I am still fussing with the gain, but it will be close to 2 e-
per ADU when I am done.  This to match the 80,000 e- to most of the 64k 16
bit ADC range.

>Ie:
>
>Dec of -30 to 90 degrees - I assume that this is local to the camera, as you
>are after southern locations.

We expect to cover from the pole to the horizon.  There is a "limit switch"
that can be set anywhere.  One then makes movements relative to this
reference position.  You can go past the switch position.  I have not yet
calibrated this motion, so I can't give you that.  But I think one will be
able to position to 10 minutes of arc or so.  This is not a great drive.
It is a chain drive and so has backlash, however there is a clamp, so if
you come from one direction always, and the wind is not blowing too much,
then you should always come to the same position by going to the limit and
then making so many steps from the limit.  This should usually take tens of
seconds.

I would set the limit switch at one end of the Dec. practical range, then
move to it and back off to set a new Dec. position.  Note the sequence is:

Unclamp
Move to limit
Move to position
Clamp

>
>HA +- 1 Hour

It will be a little more than this.  +/- 20 degrees at least.  But accuracy
may suffer at the limits.

>
>Movement in Dec of 12 degrees per second

This is roughly correct.

>
>Movement in HA of 1 degree per second
>

Presently this is way off.  I move in RA at 15 degrees per hour.  I move
backwards at 60 degrees per hour.  I have a new motor that I hope will
improve this ratio, but it will always be a problem.  i.e. you have to
think about backing off the RA drive in parallel with something else.  i.e.:

start backing noting the time
start read out
when read out is done, note the time to check where you are -one may have
gone into the stop, the motor just stalls (I hope).
continue back up motion if stil needed, else back of the limit stop and
move back in.
OK, this is a mess, I am working on it.


>Field of view of 4.3 square degrees
>

4.3 x 4.3 sq degrees = 16 sq degrees.  OK, you can figure it out exactly
400mm focal length, 15 u pixels, 2030 useful pixels.  (16 of 2048 are
covered).

>Exposure from 10 seconds to 1000 seconds.
>

No limit, you time it.  Shutter takes about 0.1 second to open or close.
It is built like a parlor door.  I.e the two haves slide away from each
other to make the opening.  So the middle gets exposed more by 0.2 second
from the edges.

Available commands:
Open shutter(n)
Close shutter(n)

Thus the two cameras do not have to have the same exposure length.  One
should allow for this so that the V camera can be programmed for a longer
exposure.

>Read out time of 50 seconds.

It is about 47 seconds.  I have made some prom changes that extends it
somewhat so that a longer cable can be driven (or a shorter cable more
reliably).

>
>I'll need to know these you I can get the timing sorted out for the
scheduler.
>
>Thanks, Peter
>
>--
>Peter T Mount      peter@retep.org.uk                Tel +44 (0) 7990 898443
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