Variable frequency delay

[Nikyu]

I have a strobe light which is used to view rotating machinery. It
uses a magnetic tach sensor which has a 0 - 5V output. The output
goes directly into the strobe. I would like to be able to rotate the
image captured by the strobe. Basically, I want to delay the 0 - 5V
signal from the tach by something on the order of 1 ms. The big
problem is the frequency of the rotating equipment is not constant, it
can range from 0 to 2500 rpm. So depending on the angular speed, a 1
ms delay would cause a different angular shift in the image I see.

What I want is about a 15 degree rotation of the captured image and
slow and high speeds.

Any ideas?

Thanks!

Eric

 

[Jasen Betts]

On 2009-02-16, Nikyu <eryk33@netscape.net> wrote:

I have a strobe light which is used to view rotating machinery. It
uses a magnetic tach sensor which has a 0 - 5V output. The output
goes directly into the strobe. I would like to be able to rotate the
image captured by the strobe. Basically, I want to delay the 0 - 5V
signal from the tach by something on the order of 1 ms. The big
problem is the frequency of the rotating equipment is not constant, it
can range from 0 to 2500 rpm. So depending on the angular speed, a 1
ms delay would cause a different angular shift in the image I see.

What I want is about a 15 degree rotation of the captured image and
slow and high speeds.

Any ideas?

get 23 more sensors and a 24 way switch?

possibly something could be done with a microcontroller
something with a timer with PWM and event capture and a few lines of
code.

there's an analogue solution too

in ramp peak |\
---generator-+-detector---rheostat---| \
| comparator -- edge --- out
`-----------------------| / detector
|/

 

[Bob Masta]

On Mon, 16 Feb 2009 08:09:18 -0800 (PST), Nikyu
<eryk33@netscape.net> wrote:

I have a strobe light which is used to view rotating machinery. It
uses a magnetic tach sensor which has a 0 - 5V output. The output
goes directly into the strobe. I would like to be able to rotate the
image captured by the strobe. Basically, I want to delay the 0 - 5V
signal from the tach by something on the order of 1 ms. The big
problem is the frequency of the rotating equipment is not constant, it
can range from 0 to 2500 rpm. So depending on the angular speed, a 1
ms delay would cause a different angular shift in the image I see.

What I want is about a 15 degree rotation of the captured image and
slow and high speeds.

Any ideas?

Thanks!

Eric

You can do this with a dual-slope ramp scheme.
The input pulse switches on an input current to an
integrator that ramps up at rate dependent on the
phase delay you want. The integrator output goes
to a comparator, and when it hits threshold it
disconnects the charging current and connects a
*constant* discharge current. That ramps the
integrator down until the next input pulse starts
the cycle over again. The comparator output is a
rectangular wave that is delayed by an amount
controlled by the up-ramp current.

I used this approach back in the mid-1970s while
working for GM's Cadillac division, to provide a
simple (cheap) way to control ignition timing
without an on-board computer. Various switches
(manifold pressure, temperature, engine speed)
combined in a simple diode logic array to select
the charging current for the desired spark advance
at various running conditions. Worked great, cost
only 10% what a computer would have cost but gave
90% of the benefits. But I think they only used
it for one or two years, and only on a few models,
before computers took over.

Best regards,


Bob Masta

DAQARTA v4.51
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!

 

[H]

On Mon, 16 Feb 2009 08:09:18 -0800 (PST), Nikyu <eryk33@netscape.net>
wrote:

I have a strobe light which is used to view rotating machinery. It
uses a magnetic tach sensor which has a 0 - 5V output. The output
goes directly into the strobe. I would like to be able to rotate the
image captured by the strobe.

The simple, foolproof method would be to move the magnetic sensor or
the magnet. I assume that is not an acceptable option?

An even simpler option would be to simply buy a timing light which has
this functionality built-in. Not a very fun solution, though.

Basically, I want to delay the 0 - 5V
signal from the tach by something on the order of 1 ms. The big
problem is the frequency of the rotating equipment is not constant, it
can range from 0 to 2500 rpm. So depending on the angular speed, a 1
ms delay would cause a different angular shift in the image I see.

What I want is about a 15 degree rotation of the captured image and
slow and high speeds.

Obviously, 15 degree delay is not possible at zero speed. You will
have to define a minimum required speed.

Depending on how low you have to go, this problem should not be too
difficult with a microcontroller and a bit of arithmetic. You'd have
to time one complete revolution (the time between two pulses), and
then delay the next pulse by 1/24 of that value. This method assumes
that the speed does not change between two consecutive revolutions, so
it would only be accurate at constant speeds.

 

[Nobody]

On Mon, 16 Feb 2009 08:09:18 -0800, Nikyu wrote:

I have a strobe light which is used to view rotating machinery. It
uses a magnetic tach sensor which has a 0 - 5V output. The output
goes directly into the strobe. I would like to be able to rotate the
image captured by the strobe. Basically, I want to delay the 0 - 5V
signal from the tach by something on the order of 1 ms. The big
problem is the frequency of the rotating equipment is not constant, it
can range from 0 to 2500 rpm. So depending on the angular speed, a 1
ms delay would cause a different angular shift in the image I see.

What I want is about a 15 degree rotation of the captured image and
slow and high speeds.

Any ideas?

Use a microcontroller. I can't think of a solution using discretes which
isn't significantly more complex.

The obvious discrete solution is a phase-locked loop (PLL) with a 12-stage
twisted ring counter as the divider. That gives you 24 signals at the same
frequency as the input, with phase shifts in 15-degree steps.

A much simpler solution is an absolute delay which can be varied via a
knob. You manually adjust the knob until you're looking at the right part.
This assumes that the speed doesn't vary while you're looking at it.

 

[whit3rd]

On Feb 16, 8:09 am, Nikyu <ery...@netscape.net> wrote:

I have a strobe light which is used to view rotating machinery.  It
uses a magnetic tach sensor which has a 0 - 5V output.  The output
goes directly into the strobe.  I would like to be able to rotate the
image captured by the strobe.

So, use a phase-locked loop (CD4046 type) with one or
two decoded counters (CD4017 type) in the reference
branch. That will give you ten to twenty taps at
various phases with respect to the input.