#### Risetime calculator (in tekwiki)

Tim Phillips

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.

http://w140.com/tekwiki/wiki/Risetime_Calculator

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

thanks
Tim P

Albert Otten

Ideally you would use pots (as variable resistors) for which the resistance increases quadratically from ccw to cw. Then compare the sum of the first 3 resistances with the 4th resistance in a bridge circuit and tune the 4th pot to zero reading. I don't think that the quadratic behavior can be approached good enough with log pots and some trimpots and extra resistors.

Albert

On Fri, Jan 17, 2020 at 08:31 AM, Tim Phillips wrote:

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.

http://w140.com/tekwiki/wiki/Risetime_Calculator

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

thanks
Tim P

Leo Bodnar

It can be also done with linear pots and quadratic scale markings around the pot.
Or a slide rule with two sliders.
Leo

GerryR <totalautomation1@...>

Is there a Tek part number associated with this unit? How is it used to calculate rise time?
Thanks,
GerryR

----- Original Message -----
From: "Tim Phillips" <timexucl@gmail.com>
To: <TekScopes@groups.io>
Sent: Friday, January 17, 2020 2:32 AM
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.

http://w140.com/tekwiki/wiki/Risetime_Calculator

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

thanks
Tim P

Jean-Paul

I have the circular slide rule version, Tektronix Circuit Computer (TEK 003-023) circa 1961, risetime, resonance, impedance, etc.
https://vintagetek.org/tektronix-circuit-computer/

Any others have one?
Looking for another one!

Jon

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 things.

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: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Tim Phillips
Sent: Thursday, January 16, 2020 11:32 PM
To: TekScopes@groups.io
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.

http://w140.com/tekwiki/wiki/Risetime_Calculator

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

thanks
Tim P

--
Dennis Tillman W7PF
TekScopes Moderator

amirb

there are no opamps or any active device in this thing as far as I can tell. so no analog computer... See the picture...
only a bunch of resistors in some kind of bridge which must be balanced but why it will produce RMS beats me

On Fri, Jan 17, 2020 at 10:54 AM, Dennis Tillman W7PF wrote:

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 things.

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: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Tim
Phillips
Sent: Thursday, January 16, 2020 11:32 PM
To: TekScopes@groups.io
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.

http://w140.com/tekwiki/wiki/Risetime_Calculator

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

thanks
Tim P

--
Dennis Tillman W7PF
TekScopes Moderator

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 <dennis@ridesoft.com>
wrote:

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
things.

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: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Tim
Phillips
Sent: Thursday, January 16, 2020 11:32 PM
To: TekScopes@groups.io
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.

http://w140.com/tekwiki/wiki/Risetime_Calculator

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

thanks
Tim P

--
Dennis Tillman W7PF
TekScopes Moderator

Hi Tim,
When I was in high school my friend and I built an analog computer with 2 pots and a meter. It multiplied two numbers together and displayed the result on the meter.
When we showed it to my friend's sister she asked us to multiply 2x3.
The result we got was around 8 on the meter. It could have been 9 or 7. It was hard to tell.
She was not impressed.

We looked around for something better to do with our budding career in electronics.
There wasn't much. The only "instrument" I owned was a VTVM. That limits your options.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Albert Otten
Sent: Friday, January 17, 2020 1:15 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Risetime calculator (in tekwiki)

Ideally you would use pots (as variable resistors) for which the resistance increases quadratically from ccw to cw. Then compare the sum of the first 3 resistances with the 4th resistance in a bridge circuit and tune the 4th pot to zero reading. I don't think that the quadratic behavior can be approached good enough with log pots and some trimpots and extra resistors.

Albert

On Fri, Jan 17, 2020 at 08:31 AM, Tim Phillips wrote:

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.

http://w140.com/tekwiki/wiki/Risetime_Calculator

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

thanks
Tim P

--
Dennis Tillman W7PF
TekScopes Moderator

Bruce Atwood

Just as an op-amp (with negative feedback) nulls the voltage between the
inverting and non-inverting inputs here the nulling is done with wetware
and the center zero meter.

On 1/17/2020 10:57 AM, amirb wrote:
there are no opamps or any active device in this thing as far as I can tell. so no analog computer... See the picture...
only a bunch of resistors in some kind of bridge which must be balanced but why it will produce RMS beats me
On Fri, Jan 17, 2020 at 10:54 AM, Dennis Tillman W7PF wrote:

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 things.

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: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Tim
Phillips
Sent: Thursday, January 16, 2020 11:32 PM
To: TekScopes@groups.io
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.

https://urldefense.com/v3/__http://w140.com/tekwiki/wiki/Risetime_Calculator__;!!KGKeukY!jGwTq9kVenN9hphTkjChf-o92VKRzY8LCY0yndo2kwjW0iBcvbYRWHB5DdUxKH41\$

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

thanks
Tim P

--
Dennis Tillman W7PF
TekScopes Moderator

.
--
Bruce Atwood PhD
Department of Astronomy
The Ohio State University
100 West 18th Ave., Room 4055
Columbus, OH 43210

Phone 614.314.0189
FAX 614.292.2928

Chuck Harris

Of course it is an analog computer!

It is using the sum of three log pots to balance with a fourth
to get a result that is read on the fourth dial.

That makes it a computer.

Read some history. Early computers didn't necessarily have any
active components. Think slide rule.

-Chuck Harris

amirb wrote:

there are no opamps or any active device in this thing as far as I can tell. so no analog computer... See the picture...
only a bunch of resistors in some kind of bridge which must be balanced but why it will produce RMS beats me
On Fri, Jan 17, 2020 at 10:54 AM, Dennis Tillman W7PF wrote:

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

Scott Singelyn

Jean-Paul, very cool calculator! Is there any chance that it could be taken apart and each disk scanned? If it could, then I think we could make a paper cut-out version to play with.
Thanks for sharing.

n4buq

Sounds like the system had lost its calibration data; however, 2 x 3 does equal 8 for large values of 3.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Dennis Tillman W7PF" <dennis@ridesoft.com>
To: TekScopes@groups.io
Sent: Friday, January 17, 2020 10:02:17 AM
Subject: Re: [TekScopes] Risetime calculator (in tekwiki)

Hi Tim,
When I was in high school my friend and I built an analog computer with 2
pots and a meter. It multiplied two numbers together and displayed the
result on the meter.
When we showed it to my friend's sister she asked us to multiply 2x3.
The result we got was around 8 on the meter. It could have been 9 or 7. It
was hard to tell.
She was not impressed.

We looked around for something better to do with our budding career in
electronics.
There wasn't much. The only "instrument" I owned was a VTVM. That limits your
options.

Dennis Tillman W7PF

Jason A.

I would love to have one of those Tektronix Circuit Computers too! I've been watching for one to show up and have never found one yet. Jon, do you have a 3d printer? I bet you could make copies and sell them! :-) You probably wouldn't get rich doing so, but Like the VTCT Dennis came up with, you'd probably have more demand than either of us would have thought...

Roy Thistle

On Fri, Jan 17, 2020 at 03:30 AM, GerryR wrote:

How is it used to calculate rise time?
Hi GerryR, Hi All:
If I remember correctly....
If T = the total rise time of a cascaded system, and
ti for I = 1 to n is the rise time for each of the n subsystems, of the cascaded system.
then, for n =3, as for example in the Tektronix unit
T = sqrt( t1^2 + t2^2 + t3^2 )
so the unit computes the overall risetime of a cascaded system, supposing you know the rise times of the three cascaded systems.
Doing it with a slide rule requires finding three squares on the slide rule, 3 copies, two hand additions, and a final square root operation on the slide rule... versus 4 operations on the Tektronix unit. I'd rather use the Tektronix unit... and unless there was a large, very well made, slide rule available, the Tektronix unit was probably as accurate for the final result... or the answers it gave were good enough.
Best wishes and regards.
Roy

Roy Thistle

On Fri, Jan 17, 2020 at 07:57 AM, amirb wrote:

why it will produce RMS
Hi amirb, et. al.:
If by RMS you mean "root mean square" … and if there are three cascaded systems with, for example, 90 degree phase shift each.... and if the cascade is driven by a sinusoidal input... then, you could use the Tektronix unit to determine the overall RMS output, of the cascaded system.
Since, the RMS values of the inputs to each subsystem are orthogonal...because of the phase shift.
And RMSout = sqrt( RMS1^2 + RMS2^2 + RMS3^2 )
Best regards and wishes.
Roy
P.S. You might have meant, why the circuit with do that above calculation... or any other calculations. If so, see the other posts in this thread, for an explanation.

Hi Barry,
I didn't thinking of telling that to Andrea, my friend's sister, at the time. I doubt she would have bought it.
Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of n4buq
Sent: Friday, January 17, 2020 9:01 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Risetime calculator (in tekwiki)

Sounds like the system had lost its calibration data; however, 2 x 3 does equal 8 for large values of 3.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Dennis Tillman W7PF" <dennis@ridesoft.com>
To: TekScopes@groups.io
Sent: Friday, January 17, 2020 10:02:17 AM
Subject: Re: [TekScopes] Risetime calculator (in tekwiki)

Hi Tim,
When I was in high school my friend and I built an analog computer
with 2 pots and a meter. It multiplied two numbers together and
displayed the result on the meter.
When we showed it to my friend's sister she asked us to multiply 2x3.
The result we got was around 8 on the meter. It could have been 9 or
7. It was hard to tell.
She was not impressed.

We looked around for something better to do with our budding career in
electronics.
There wasn't much. The only "instrument" I owned was a VTVM. That

Dennis Tillman W7PF

--
Dennis Tillman W7PF
TekScopes Moderator

Hi Jason,
I have never seen one of these before the other day but I can reproduce the analog computer my friend and I made when we were in high school as a substitute until you find the Tektronix one. It had a beautiful Formica wood grain front panel to impress people. I can even put something that looks like a Tek logo on it. Let me know. :)
Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jason A. via Groups.Io
Sent: Friday, January 17, 2020 12:31 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Risetime calculator (in tekwiki)

I would love to have one of those Tektronix Circuit Computers too! I've been watching for one to show up and have never found one yet. Jon, do you have a 3d printer? I bet you could make copies and sell them! :-) You probably wouldn't get rich doing so, but Like the VTCT Dennis came up with, you'd probably have more demand than either of us would have thought...

--
Dennis Tillman W7PF
TekScopes Moderator

amirb

Roy
sorry my mistake, I only meant why/how this thing can calculate square root of sum of squares (should not have used rms for that perhaps)
obviously there are no sinusoidal voltages or anything like that in this device.

and so far nobody here knows exactly how this device works. Yes it is based on a bridge that when balanced you can read the answer on the
4th pot, That operation was pretty obvious by looking at the front panel. It appears to only have bunch of resistors (5 pots for calibration and 4 on the front panel plus
bunch of fixed resistors) and yet it does a nonlinear calculation or at least approximates a nonlinear expression that involves square root, but how?
nobody has explained that really.

It seems that it must be balancing the power in one resistor (4th pot) with the sum of powers in three other resistors!
but I have not seen a bridge that can do this...

I tried to draw the schematics by looking at that picture but I got lost in the middle of it...

On Fri, Jan 17, 2020 at 08:50 PM, Roy Thistle wrote:

On Fri, Jan 17, 2020 at 07:57 AM, amirb wrote:

why it will produce RMS
Hi amirb, et. al.:
If by RMS you mean "root mean square" … and if there are three cascaded
systems with, for example, 90 degree phase shift each.... and if the cascade
is driven by a sinusoidal input... then, you could use the Tektronix unit to
determine the overall RMS output, of the cascaded system.
Since, the RMS values of the inputs to each subsystem are orthogonal...because
of the phase shift.
And RMSout = sqrt( RMS1^2 + RMS2^2 + RMS3^2 )
Best regards and wishes.
Roy
P.S. You might have meant, why the circuit with do that above calculation...
or any other calculations. If so, see the other posts in this thread, for an
explanation.

Harvey White

Perhaps I can help a bit.

Look at some of the sliderule scales if you can.  If you wanted to do addition, the scales would be linear.  If you wanted to do multiplication, they would not be.  You move the slides and 2*2 aligns with 4.  4*4 aligns with 16.  If you had pots, then while the pots can be linear, and you may or may not compute each step as if it were linear (and you probably wouldn't), when you balance the bridge, you want the final pot to read a value that's the result of the equation.

in other words, if you have 1 and 1, the result scale needs to balance at 1.  If you have 2 and 2, the result scale needs to balance at 1.414 * 2, or 2.828.  Mark that value as 2.828.  You have to balance the two legs to an equal voltage.  Even if the pots are linear, you mark them with the appropriate scale values to solve the equation.

Harvey

On 1/17/2020 10:48 PM, amirb wrote:
Roy
sorry my mistake, I only meant why/how this thing can calculate square root of sum of squares (should not have used rms for that perhaps)
obviously there are no sinusoidal voltages or anything like that in this device.

and so far nobody here knows exactly how this device works. Yes it is based on a bridge that when balanced you can read the answer on the
4th pot, That operation was pretty obvious by looking at the front panel. It appears to only have bunch of resistors (5 pots for calibration and 4 on the front panel plus
bunch of fixed resistors) and yet it does a nonlinear calculation or at least approximates a nonlinear expression that involves square root, but how?
nobody has explained that really.

It seems that it must be balancing the power in one resistor (4th pot) with the sum of powers in three other resistors!
but I have not seen a bridge that can do this...

I tried to draw the schematics by looking at that picture but I got lost in the middle of it...

On Fri, Jan 17, 2020 at 08:50 PM, Roy Thistle wrote:

On Fri, Jan 17, 2020 at 07:57 AM, amirb wrote:

why it will produce RMS
Hi amirb, et. al.:
If by RMS you mean "root mean square" … and if there are three cascaded
systems with, for example, 90 degree phase shift each.... and if the cascade
is driven by a sinusoidal input... then, you could use the Tektronix unit to
determine the overall RMS output, of the cascaded system.
Since, the RMS values of the inputs to each subsystem are orthogonal...because
of the phase shift.
And RMSout = sqrt( RMS1^2 + RMS2^2 + RMS3^2 )
Best regards and wishes.
Roy
P.S. You might have meant, why the circuit with do that above calculation...
or any other calculations. If so, see the other posts in this thread, for an
explanation.

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