Can I swap a cer. resonator for an xtal?

[Isaac Wingfield]

<http://www.jameco.com/cgi-
bin/ncommerce3/ExecMacro/jameco/searchResult.d2w/report?sort=BPA&search=1378
16
which states 17pF, the two 30pF caps currently in the circuit would be

fine?

Sounds about right.

There are two main types of crystals. Parallel resonant, and series
resonant.[/QUOTE]

That's a common belief, but it's not true. A crystal can be operated in
either mode; what that specification tells you, is which way to operate
the crystal to have it oscillate at its specified frequency (in other
words, that's how the manufacturer operated it, to measure it, and
*that* is why the parallel capacitance is specified). It'll operate in
the other mode just fine, but at a slightly different frequency; that's
all. Many times, that difference in frequency is of absolutely no
significance.

Isaac

 

[Isaac Wingfield]

Certainly it wouldn't be of significance if a resonator was good
enough.

No real-life resonator is that good. What matters is the precision of
frequency necessary for the task at hand. Sometimes the difference
between the series resonant frequency and the parallel resonant
frequency *for any crystal you can buy*, is an error that is simply not
tolerable.

OTOH, sometimes the precise frequency is of no concern whatsoever, and
it's fine to be somewhere close, but fairly stable. That would be the
case for almost all computer system clock applications, for example.

Isaac

 

[Da Man]

Removed all caps & tested with cap tester.

What's the ESR of the electrolitic caps?

 

[DaveC]

What's the ESR of the electrolitic caps?

Criminy, I don't know. Can the ESR really change that much without the
capacitance value not changing?

Is there a way to measure this with a meter -- that is, a commonly-available,
meter, not an ESR meter (if there is such a thing...)?

Regards,

 

[James Sweet]

Criminy, I don't know. Can the ESR really change that much without the
capacitance value not changing?

Is there a way to measure this with a meter -- that is, a commonly-available,
meter, not an ESR meter (if there is such a thing...)?

Yes and no, if in doubt try replacing caps.

 

[Spehro Pefhany]

Yes and no, if in doubt try replacing caps.

Or just tack one of roughly equal value and at least as high voltage
rating across the suspect cap....


Best regards,
Spehro Pefhany

 

[Fred Abse]

What's the ESR of the electrolitic caps?

We don't live in a perfect world, hence the perfect capacitor of circuit
theory doesn't really exist. Capacitors are made out of real materials
which are less than perfect. The leads are made of some metal or another,
which has resistance, they are attached to the plates, which are made out
of something which has resistivity, in the case of electrolytic
capacitors, one "plate" is actually a solution of chemicals in one form or
another. No dielectric is perfect either, all have losses which can be
expressed as a resistance.

All these imperfections add up, so what we have is what appears at the
terminals as a "perfect" capacitor in series with a resistance.

This is called the equivalent series resistance (ESR). "Equivalent"
because it is the cumulative effect of many different losses.

This is true for all capacitors, but electrolytic capacitors exhibit the
highest values of ESR.

You will also come across the term "loss angle". This is just a different
way of expressing the same thing, and is the difference between the actual
phase angle of the component and the -90 degrees of a perfect capacitor.

Summing up; a perfect capacitor does not dissipate power, real capacitors
do, and ESR is one way of expressing this.