Re: Risetime calculator (in tekwiki)

Tony Fleming

Thanks for sharing! You had a great job, despite stress and push to work
24/7 .... if the management could do that.
I wish I was working in a group like you did, the learning curve and new
"thinking" was a greatest teacher!
Have a great day!

On Fri, Jan 17, 2020 at 9:54 AM Dennis Tillman W7PF <>

Hi Tim,
It is an ANALOG computer. These were very commonly used for many things
but that was probably before you were born.
I got my first real job in 1967 working in a huge lab at Allied Aerospace
that designed airplane autopilots and flight control systems. Until a year
later these were always analog computers. To design the airplane's analog
flight control computer to have the right characteristics a team had to
measure the airplane's response to various (controlled) inputs such as how
it responded when commanded to make a sharp turn.

The job of the airplane's analog computer was to take that raw response
which was converted into an equation and create another equation that had
the response the customer (an airline) wanted. Presumably that would be to
turn the sharp bumpy turn into something gentle and smooth. This was all
done on a precision analog computer that had a plug board that was at least
6ft by 10ft long. Various modules (OpAmps, inductances, capacitances,
resistances, etc.) could be easily connected together and modified until
the engineers were satisfied with the results.

The final configuration was converted back into an equation and then a
different group of engineers took those equations and using OpAmp modules,
from companies like Philbrick Research, put it all together in a small box
that ultimately became the autopilot for that plane. By the time I arrived
Allied Aerospace was using newly developed OpAmp ICs such as the uA709. I
remember when I was only on the job for a few weeks and I blew one of those
uA709s out. I was really scared that I would be chewed out. Those things
cost $50 each because they were so new. The OpAmp ICs revolutionized
everything we did. Suddenly the autopilot could be smaller and do more

2 years later digital ICs were beginning to be reliable enough that they
could be used in parts of the autopilot. I worked on the Concorde Autopilot
that was done with this new family of DIGITAL logic called DTL. It had a
lot of details you had to be careful about like needing pull up resistors
in certain cases. Those caused trouble for a while. The problems were
solved eventually.
For a few years after that the autopilots were a mixture of analog and
digital ICs. Most of the autopilot was analog, and parts like VOTER
circuits, which decided which of the three autopilot results (everything is
triple redundant in an autopilot) is correct, were digital. This was done
with analog comparators and digital logic. If something should go bad with
one of the three autopilots the voter circuit disconnects it and relies on
the other two autopilot results.

Dennis Tillman W7PF

-----Original Message-----
From: [] On Behalf Of Tim
Sent: Thursday, January 16, 2020 11:32 PM
Subject: [TekScopes] Risetime calculator (in tekwiki)

from Tim P (UK)
What is this, please? It seems to be a simple analog computer, maybe with
Log pots.
In case the link doesn't work, the device is in tekwiki Other Instruments.

Appears to give f = sqrt(a^2 + b^2 + c^2)

Tim P

Dennis Tillman W7PF
TekScopes Moderator

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