I/P values too high ... need help here
Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
Hey Bogus ,
Thanks for the info.
What you are describing is called an 'integrator' and it's used to shape a squarewave signal or 'round' off the edges.
Normally they are comprised of some resistive and capacitive componnents and possibly an inductive component as well.
I'm not too sure why the squarewave needs to be shaped into more of a sinusoidal waveform as digital circuits are triggered by squarewaves.
The trigger occurs either on the leading or trailing edge of the waveform.
I'm figuring (guessing
) the tach filter is some value of capacitance (and maybe inductance) that filters the harmonics created by the magnetic field created when the coil current collapses to create the secondary ignition voltage.
Probably to keep form double or triple triggering the input circuit on the extra excursions in the harmonics.
That's what has been so puzzling to me. How can a digital circuit be off 'just a little' ? Usually they are right or don't work at all.
I suppose since the TACH meter is an analog device somewhere there is a DA converter that drives the meter movement. Seems that is where a calibration capability would be to set these things correctly.
Anyway I thought I must be the only one with a tach indicating incorrectly.
Looks as if I'm not alone.
Maybe we'll get more information from someone else out there.
Thanks for the info.
What you are describing is called an 'integrator' and it's used to shape a squarewave signal or 'round' off the edges.
Normally they are comprised of some resistive and capacitive componnents and possibly an inductive component as well.
I'm not too sure why the squarewave needs to be shaped into more of a sinusoidal waveform as digital circuits are triggered by squarewaves.
The trigger occurs either on the leading or trailing edge of the waveform.
I'm figuring (guessing
) the tach filter is some value of capacitance (and maybe inductance) that filters the harmonics created by the magnetic field created when the coil current collapses to create the secondary ignition voltage.Probably to keep form double or triple triggering the input circuit on the extra excursions in the harmonics.
That's what has been so puzzling to me. How can a digital circuit be off 'just a little' ? Usually they are right or don't work at all.
I suppose since the TACH meter is an analog device somewhere there is a DA converter that drives the meter movement. Seems that is where a calibration capability would be to set these things correctly.
Anyway I thought I must be the only one with a tach indicating incorrectly.
Looks as if I'm not alone.
Maybe we'll get more information from someone else out there.
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
Originally Posted by bogus
I am not sure if it's all that simple... the filter takes out the square wave so the tach can display the RPMs more accurately. Without it, the tach would be jumping like crazy.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Originally Posted by VetNutJim
Hey Bogus ,
Thanks for the info.
What you are describing is called an 'integrator' and it's used to shape a squarewave signal or 'round' off the edges.
Normally they are comprised of some resistive and capacitive componnents and possibly an inductive component as well.
I'm not too sure why the squarewave needs to be shaped into more of a sinusoidal waveform as digital circuits are triggered by squarewaves.
The trigger occurs either on the leading or trailing edge of the waveform.
I'm figuring (guessing) the tach filter is some value of capacitance (and maybe inductance) that filters the harmonics created by the magnetic field created when the coil current collapses to create the secondary ignition voltage.
Probably to keep form double or triple triggering the input circuit on the extra excursions in the harmonics.
Thanks for the info.
What you are describing is called an 'integrator' and it's used to shape a squarewave signal or 'round' off the edges.
Normally they are comprised of some resistive and capacitive componnents and possibly an inductive component as well.
I'm not too sure why the squarewave needs to be shaped into more of a sinusoidal waveform as digital circuits are triggered by squarewaves.
The trigger occurs either on the leading or trailing edge of the waveform.
I'm figuring (guessing
) the tach filter is some value of capacitance (and maybe inductance) that filters the harmonics created by the magnetic field created when the coil current collapses to create the secondary ignition voltage.Probably to keep form double or triple triggering the input circuit on the extra excursions in the harmonics.
That's what has been so puzzling to me. How can a digital circuit be off 'just a little' ? Usually they are right or don't work at all.
I suppose since the TACH meter is an analog device somewhere there is a DA converter that drives the meter movement. Seems that is where a calibration capability would be to set these things correctly.
Anyway I thought I must be the only one with a tach indicating incorrectly.
Looks as if I'm not alone.
Maybe we'll get more information from someone else out there.
I suppose since the TACH meter is an analog device somewhere there is a DA converter that drives the meter movement. Seems that is where a calibration capability would be to set these things correctly.
Anyway I thought I must be the only one with a tach indicating incorrectly.
Looks as if I'm not alone.
Maybe we'll get more information from someone else out there.
Thread Starter
6th Gear
Joined: Jan 2005
Posts: 6
Likes: 0
According to the electric diagram it seems to be a double capacitor with a bridge to ground. This means that with a bad ground, the final voltage output will be too high, but still stable. With a broken filter it would probably do exactly like Bogus says, jump like crazy.
It stopped raining this morning, so I went to have a look at the location again, which I can't reach in any way without getting the distributor out of the way !@#$%!@#!!! And of course so far the only tool that always fits is my hammer... I have good hope that the problem is over as soon as I can get to clean up the ground of the tach filter. Through all the wires, cables and vacuum tubes it doesn't seem to be all shiny and new behind the engine...
P.
It stopped raining this morning, so I went to have a look at the location again, which I can't reach in any way without getting the distributor out of the way !@#$%!@#!!! And of course so far the only tool that always fits is my hammer... I have good hope that the problem is over as soon as I can get to clean up the ground of the tach filter. Through all the wires, cables and vacuum tubes it doesn't seem to be all shiny and new behind the engine...
P.
