Empathy List Archives

W

Will

Fri, Jan 13, 2012 9:11 PM

Extremely low value (3 terminal!) standard capacitors are usually
constructed using a metal plate (guard) with a small aperture hole in
center and two parallell metal plates (the capacitor) on both sides of
the guard. The capacitance is adjusted by changing the distance of the
plates and the size of the aperture.

2012/1/13, Fred Schneider pa4tim@gmail.com:

I need something that gives a known capacitance around 1 pF.

Extremely low value (3 terminal!) standard capacitors are usually constructed using a metal plate (guard) with a small aperture hole in center and two parallell metal plates (the capacitor) on both sides of the guard. The capacitance is adjusted by changing the distance of the plates and the size of the aperture. 2012/1/13, Fred Schneider <pa4tim@gmail.com>: > I need something that gives a known capacitance around 1 pF.

W

Will

Fri, Jan 13, 2012 10:12 PM

Poul-Henning Kamp wrote:

Actually the major trouble with Peltier is controlling them, because
they are asymetric with respect to transport direction.

I think the negative feedback of the control loop helps with that,
unless the difference is so big that it requires different
compensation for cooling and heating to be stable.

Andreas Jahn wrote:

What about this?
http://www.eevblog.com/2010/07/25/eevblog-101-hacking-your-own-peltier-lab-thermal-chamber/

Seeing the internals of Peltier fridge on the video gave me some ideas. Thanks.

But I think I still try to build something by myself... All comments
and ideas are very welcome.

Poul-Henning Kamp wrote: >Actually the major trouble with Peltier is controlling them, because >they are asymetric with respect to transport direction. I think the negative feedback of the control loop helps with that, unless the difference is so big that it requires different compensation for cooling and heating to be stable. Andreas Jahn wrote: >What about this? >http://www.eevblog.com/2010/07/25/eevblog-101-hacking-your-own-peltier-lab-thermal-chamber/ Seeing the internals of Peltier fridge on the video gave me some ideas. Thanks. But I think I still try to build something by myself... All comments and ideas are very welcome.

PK

Poul-Henning Kamp

Fri, Jan 13, 2012 10:19 PM

In message CAE6XXriOVmmkLr2K6jZFdHurtYbYyCbGZcRLExQ=rvMcDFk2jw@mail.gmail.com
, Will writes:

Poul-Henning Kamp wrote:

Actually the major trouble with Peltier is controlling them, because
they are asymetric with respect to transport direction.

I think the negative feedback of the control loop helps with that,
unless the difference is so big that it requires different
compensation for cooling and heating to be stable.

Depends on the temperature difference but I seem to recall that it
is something like 1:3.

The problem is that once you get to your target temperature, it will
fuddle around with the small residual noise and because of the
asymetry it actually amplifies the noise if you don't do something
to prevent it.

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

In message <CAE6XXriOVmmkLr2K6jZFdHurtYbYyCbGZcRLExQ=rvMcDFk2jw@mail.gmail.com> , Will writes: >Poul-Henning Kamp wrote: > >>Actually the major trouble with Peltier is controlling them, because >>they are asymetric with respect to transport direction. > >I think the negative feedback of the control loop helps with that, >unless the difference is so big that it requires different >compensation for cooling and heating to be stable. Depends on the temperature difference but I seem to recall that it is something like 1:3. The problem is that once you get to your target temperature, it will fuddle around with the small residual noise and because of the asymetry it actually amplifies the noise if you don't do something to prevent it. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

RS

Randy Scott

Fri, Jan 13, 2012 10:52 PM

Actually the major trouble with Peltier is controlling them, because
they are asymetric with respect to transport direction.

I think the negative feedback of the control loop helps with that,
unless the difference is so big that it requires different
compensation for cooling and heating to be stable.

Depends on the temperature difference but I seem to recall that it
is something like 1:3.

Forgive my ignorance, but does this mean that it is "harder" to cool
than it is to heat, given the same magnitude of current through the
junction?

The problem is that once you get to your target temperature, it will
fuddle around with the small residual noise and because of the
asymetry it actually amplifies the noise if you don't do something
to prevent it.

Does this depend on the manner in which you're driving the Peltier
(a "digital" control where the junction is fully-heating, fully-
cooling, or off vs. an "analog" control where the control loop
controls the magnitude and direction of current flow)?

Randy.

>>>Actually the major trouble with Peltier is controlling them, because >>>they are asymetric with respect to transport direction. >> >>I think the negative feedback of the control loop helps with that, >>unless the difference is so big that it requires different >>compensation for cooling and heating to be stable. > >Depends on the temperature difference but I seem to recall that it >is something like 1:3. Forgive my ignorance, but does this mean that it is "harder" to cool than it is to heat, given the same magnitude of current through the junction? >The problem is that once you get to your target temperature, it will >fuddle around with the small residual noise and because of the >asymetry it actually amplifies the noise if you don't do something >to prevent it. Does this depend on the manner in which you're driving the Peltier (a "digital" control where the junction is fully-heating, fully- cooling, or off vs. an "analog" control where the control loop controls the magnitude and direction of current flow)? Randy.

BS

Bob Smither

Fri, Jan 13, 2012 11:48 PM

Will wrote:

Varying room temperature is a remarkable source of error when making
measurements in home environment. It would be nice to have a simple
air bath for the items under test. And even better if it was big
enough for the multimeter too. There are commercial units available
but very expensive.

A DIY solution seems to be possible: a simple PI(D) controller built
around an NTC resistor, op-amp, pass-transistor and heater plus a fan
to keep the air moving inside the box. That approach allows
temperature higher than room temperature only but in most cases
stability is important and not the absolute value. A Peltier element
is almost as easy to drive as a heater resistor, but dissipated heat
probably makes the thermal design much more challenging.

I am not an expert and there many questionmarks related air
circulation, thermistor location and probably other things I can't
even imagine.

Hi Will,

For years I have used a modified Rival brand consumer grade convection oven as a
test chamber. Although I designed it for use up to 200C, it can be used at any
temperature above ambient.

The oven has a usefully large "cooking" chamber - 16" x 14" x 8.5". The heater
and fan are in a section above the chamber separated by a metal partition. The
heated air exits that section and enters the chamber through several slots in
the metal partition.

I redid the wiring so that the fan runs all the time and I designed a simple on
/ off controller to control the heater element. The controller is in series
with the oven bimetallic thermostat which serves as an over temperature safety
cutoff - I just set it well above the temperature I set the controller to.

The controller uses a diode that is placed in the chamber as the sensing
element. A comparator compares the diode voltage to a fixed level derived from
a reference and a 10 turn pot.

The heater is switched by a solid state relay that is controlled by the
comparator output. The SSR has the nice feature of zero voltage turn on that
reduces any electrical interference.

I have tried different placements of the diode sensor. If it is located in the
heater / fan section above the chamber the system is very over damped and it
takes a long time to reach equilibrium (the diode "overreacts" to the power
applied to the heater element and shuts down). If it is located in the chamber,
the oven will overshoot the target temperature as the applied power is not
sensed quickly enough. The best location seems to be in the chamber but close
(~1") to one of the slots where the heated air enters the chamber.

Although the SSR is an on / off device, when close to the set point it behaves
in almost an analog fashion as there is some 60 cycle pickup on the sense lead
(that goes to the diode sensor) so in fact it operates at various duty cycles as
it applies power to the heater.

I just ran an experiment with three thermocouples in the chamber at different
positions (close to wall, in middle of chamber, ...). The lowest setting on my
controller is above room temperature at 34C. Here are the minimums and maximums
through several cycles of the controller at the three different locations as
recorded on a Doric Trendicator 412A:

Position 1: 33.8C - 34.2C
Position 2: 33.7C - 34.2C
Position 3: 33.7C - 34.3C

I have used this oven for over 25 years. Recently the fan motor finally gave up
but it was easy to replace.

Hope this gives you some ideas.

Bob Smither

Will wrote: > Varying room temperature is a remarkable source of error when making > measurements in home environment. It would be nice to have a simple > air bath for the items under test. And even better if it was big > enough for the multimeter too. There are commercial units available > but very expensive. > > A DIY solution seems to be possible: a simple PI(D) controller built > around an NTC resistor, op-amp, pass-transistor and heater plus a fan > to keep the air moving inside the box. That approach allows > temperature higher than room temperature only but in most cases > stability is important and not the absolute value. A Peltier element > is almost as easy to drive as a heater resistor, but dissipated heat > probably makes the thermal design much more challenging. > > I am not an expert and there many questionmarks related air > circulation, thermistor location and probably other things I can't > even imagine. Hi Will, For years I have used a modified Rival brand consumer grade convection oven as a test chamber. Although I designed it for use up to 200C, it can be used at any temperature above ambient. The oven has a usefully large "cooking" chamber - 16" x 14" x 8.5". The heater and fan are in a section above the chamber separated by a metal partition. The heated air exits that section and enters the chamber through several slots in the metal partition. I redid the wiring so that the fan runs all the time and I designed a simple on / off controller to control the heater element. The controller is in series with the oven bimetallic thermostat which serves as an over temperature safety cutoff - I just set it well above the temperature I set the controller to. The controller uses a diode that is placed in the chamber as the sensing element. A comparator compares the diode voltage to a fixed level derived from a reference and a 10 turn pot. The heater is switched by a solid state relay that is controlled by the comparator output. The SSR has the nice feature of zero voltage turn on that reduces any electrical interference. I have tried different placements of the diode sensor. If it is located in the heater / fan section above the chamber the system is very over damped and it takes a long time to reach equilibrium (the diode "overreacts" to the power applied to the heater element and shuts down). If it is located in the chamber, the oven will overshoot the target temperature as the applied power is not sensed quickly enough. The best location seems to be in the chamber but close (~1") to one of the slots where the heated air enters the chamber. Although the SSR is an on / off device, when close to the set point it behaves in almost an analog fashion as there is some 60 cycle pickup on the sense lead (that goes to the diode sensor) so in fact it operates at various duty cycles as it applies power to the heater. I just ran an experiment with three thermocouples in the chamber at different positions (close to wall, in middle of chamber, ...). The lowest setting on my controller is above room temperature at 34C. Here are the minimums and maximums through several cycles of the controller at the three different locations as recorded on a Doric Trendicator 412A: Position 1: 33.8C - 34.2C Position 2: 33.7C - 34.2C Position 3: 33.7C - 34.3C I have used this oven for over 25 years. Recently the fan motor finally gave up but it was easy to replace. Hope this gives you some ideas. Bob Smither

F

Fred

Sat, Jan 14, 2012 12:24 AM

Nice Maual.
All you folks, thanks for the info. I have some inspiration. Think I
first try the coaxial approach. But the biggest problem will be to know
the value but a coaxial one is the most easy to measure using a VNA and
that will get me pretty close.
http://www.pa4tim.nl/?p=2929 some pictures and results op to now.

Fred

Brooke Clarke schreef op vr 13-01-2012 om 09:46 [-0800]:

Hi Fred:

Measuring components is very different from measuring things with connectors.
In order to get good answers you need to account for stray impedance as well as compensate for things like cable length.

One way to eliminate stray capacitance is to use guarding, for example see:
http://www.prc68.com/I/HP4274_4275_LCR.shtml#G

For the frequency range where they are available the four terminal pair RLC bridges are by far the most accurate method
of measuring impedance.
For more on that and a treasure trove of info on imedance measurements get a copy of the free HP Impedance Measurement
Handbook and the associated Accessories Selection Guide for Impedance Measurements. Links to those at:
http://www.prc68.com/I/Z.shtml

For really accurate impedance measurements it's best to use an "analyzer" (sweep frequency test with graphic display) as
opposed to a "meter" that has a numeric display. The better impedance analyzers have the ability to fit a number of
models to the measured complex impedance vs frequency plot and give you the circuit values.

For semiconductors their is the HP C-V meter that uses a current source to charge a capacitiance and measures the
voltage. This data plotted over time gives the semiconductor doping profile.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html

Fred Schneider wrote:

I am measuring small capacitances, just for sport but that is more difficult as I thought.
I need something that gives a known capacitance around 1 pF.
I cut several pieces FR4 in different sizes and measured them several ways, but the problem is the dielectric constant if I use K = 4.5 and distance 1.33 ( it is 1.35 thick form outside copper to outside copper so the 1.33 is also a guess) i get calculated results that are in line with my measurements. Not the same values but the same ratios.

I used a digital VNA in shunt mode, a TF1717 bridge from Marconi, the frequency shift methode as described by F.E. terman in RF measurements, a modern LCR meter ( not an expansive very good one) a function generator at 50 KHz and thn measuring the current through the capacitor, an O-opamp plugin with a setup i made to measure small currents ( delta V and delta t are constants so i measure delta i) and the last something call a Capacitance-Frequentie converter i designed, a constant DC current, a constant delta voltage integrator and comprator) and as a result a changing delta T, so frequence is related to capacitance.
All measurements are close but not enough ;-)

so I need a sturdy standard capacitance. Any suggestions, something using air will be best I think but two metal plates should be straight and mounted solid opposite. I used aluminium but forgot the dielectric constant of the oxide so it is not just air. Only if I use K=1.41 I am close. Two seperate peases of pcb ? And then there is the edge effect ect. Most formulas I find are aproximations.

I got some standard caps in the range 100-1000 pF but i want to be able to measure it in fF.

Fred PA4TIM

Op 13 jan. 2012 om 15:04 heeft "Poul-Henning Kamp"phk@phk.freebsd.dk het volgende geschreven:

In messageCAE6XXrhydntKXjzq6W8ZA46Fs048CD-Wvrcbotz7kciGd57j5Q@mail.gmail.com
, Will writes:

A Peltier element
is almost as easy to drive as a heater resistor, but dissipated heat
probably makes the thermal design much more challenging.

Actually the major trouble with Peltier is controlling them, because
they are asymetric with respect to transport direction.

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.

Nice Maual. All you folks, thanks for the info. I have some inspiration. Think I first try the coaxial approach. But the biggest problem will be to know the value but a coaxial one is the most easy to measure using a VNA and that will get me pretty close. http://www.pa4tim.nl/?p=2929 some pictures and results op to now. Fred Brooke Clarke schreef op vr 13-01-2012 om 09:46 [-0800]: > Hi Fred: > > Measuring components is very different from measuring things with connectors. > In order to get good answers you need to account for stray impedance as well as compensate for things like cable length. > > One way to eliminate stray capacitance is to use guarding, for example see: > http://www.prc68.com/I/HP4274_4275_LCR.shtml#G > > For the frequency range where they are available the four terminal pair RLC bridges are by far the most accurate method > of measuring impedance. > For more on that and a treasure trove of info on imedance measurements get a copy of the free HP Impedance Measurement > Handbook and the associated Accessories Selection Guide for Impedance Measurements. Links to those at: > http://www.prc68.com/I/Z.shtml > > For really accurate impedance measurements it's best to use an "analyzer" (sweep frequency test with graphic display) as > opposed to a "meter" that has a numeric display. The better impedance analyzers have the ability to fit a number of > models to the measured complex impedance vs frequency plot and give you the circuit values. > > For semiconductors their is the HP C-V meter that uses a current source to charge a capacitiance and measures the > voltage. This data plotted over time gives the semiconductor doping profile. > > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/Brooke4Congress.html > > > Fred Schneider wrote: > > I am measuring small capacitances, just for sport but that is more difficult as I thought. > > I need something that gives a known capacitance around 1 pF. > > I cut several pieces FR4 in different sizes and measured them several ways, but the problem is the dielectric constant if I use K = 4.5 and distance 1.33 ( it is 1.35 thick form outside copper to outside copper so the 1.33 is also a guess) i get calculated results that are in line with my measurements. Not the same values but the same ratios. > > > > I used a digital VNA in shunt mode, a TF1717 bridge from Marconi, the frequency shift methode as described by F.E. terman in RF measurements, a modern LCR meter ( not an expansive very good one) a function generator at 50 KHz and thn measuring the current through the capacitor, an O-opamp plugin with a setup i made to measure small currents ( delta V and delta t are constants so i measure delta i) and the last something call a Capacitance-Frequentie converter i designed, a constant DC current, a constant delta voltage integrator and comprator) and as a result a changing delta T, so frequence is related to capacitance. > > All measurements are close but not enough ;-) > > > > so I need a sturdy standard capacitance. Any suggestions, something using air will be best I think but two metal plates should be straight and mounted solid opposite. I used aluminium but forgot the dielectric constant of the oxide so it is not just air. Only if I use K=1.41 I am close. Two seperate peases of pcb ? And then there is the edge effect ect. Most formulas I find are aproximations. > > > > I got some standard caps in the range 100-1000 pF but i want to be able to measure it in fF. > > > > Fred PA4TIM > > > > > > > > > > > > Fred PA4TIM > > > > Op 13 jan. 2012 om 15:04 heeft "Poul-Henning Kamp"<phk@phk.freebsd.dk> het volgende geschreven: > > > >> In message<CAE6XXrhydntKXjzq6W8ZA46Fs048CD-Wvrcbotz7kciGd57j5Q@mail.gmail.com> > >> , Will writes: > >> > >>> A Peltier element > >>> is almost as easy to drive as a heater resistor, but dissipated heat > >>> probably makes the thermal design much more challenging. > >> Actually the major trouble with Peltier is controlling them, because > >> they are asymetric with respect to transport direction. > >> > >> > >> -- > >> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > >> phk@FreeBSD.ORG | TCP/IP since RFC 956 > >> FreeBSD committer | BSD since 4.3-tahoe > >> Never attribute to malice what can adequately be explained by incompetence. > >> > >> _______________________________________________ > >> volt-nuts mailing list -- volt-nuts@febo.com > >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > >> and follow the instructions there. > > _______________________________________________ > > volt-nuts mailing list -- volt-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > > > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

BC

Brooke Clarke

Sat, Jan 14, 2012 2:36 AM

Hi Fred:

You can not measure a 1 pf cap using a VNA, they are great for measuring things that are near 50 Ohms but the error
grows very fast as you move away from 50 Ohms.
Check out the error plots in the HP/Agilent Impedance Measurement Handbook for different types of measurement methods.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html

Fred wrote:

Nice Maual.
All you folks, thanks for the info. I have some inspiration. Think I
first try the coaxial approach. But the biggest problem will be to know
the value but a coaxial one is the most easy to measure using a VNA and
that will get me pretty close.
http://www.pa4tim.nl/?p=2929 some pictures and results op to now.

Fred

Brooke Clarke schreef op vr 13-01-2012 om 09:46 [-0800]:

Hi Fred:

Measuring components is very different from measuring things with connectors.
In order to get good answers you need to account for stray impedance as well as compensate for things like cable length.

One way to eliminate stray capacitance is to use guarding, for example see:
http://www.prc68.com/I/HP4274_4275_LCR.shtml#G

For the frequency range where they are available the four terminal pair RLC bridges are by far the most accurate method
of measuring impedance.
For more on that and a treasure trove of info on imedance measurements get a copy of the free HP Impedance Measurement
Handbook and the associated Accessories Selection Guide for Impedance Measurements. Links to those at:
http://www.prc68.com/I/Z.shtml

For really accurate impedance measurements it's best to use an "analyzer" (sweep frequency test with graphic display) as
opposed to a "meter" that has a numeric display. The better impedance analyzers have the ability to fit a number of
models to the measured complex impedance vs frequency plot and give you the circuit values.

For semiconductors their is the HP C-V meter that uses a current source to charge a capacitiance and measures the
voltage. This data plotted over time gives the semiconductor doping profile.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html

Fred Schneider wrote:

I am measuring small capacitances, just for sport but that is more difficult as I thought.
I need something that gives a known capacitance around 1 pF.
I cut several pieces FR4 in different sizes and measured them several ways, but the problem is the dielectric constant if I use K = 4.5 and distance 1.33 ( it is 1.35 thick form outside copper to outside copper so the 1.33 is also a guess) i get calculated results that are in line with my measurements. Not the same values but the same ratios.

I used a digital VNA in shunt mode, a TF1717 bridge from Marconi, the frequency shift methode as described by F.E. terman in RF measurements, a modern LCR meter ( not an expansive very good one) a function generator at 50 KHz and thn measuring the current through the capacitor, an O-opamp plugin with a setup i made to measure small currents ( delta V and delta t are constants so i measure delta i) and the last something call a Capacitance-Frequentie converter i designed, a constant DC current, a constant delta voltage integrator and comprator) and as a result a changing delta T, so frequence is related to capacitance.
All measurements are close but not enough ;-)

so I need a sturdy standard capacitance. Any suggestions, something using air will be best I think but two metal plates should be straight and mounted solid opposite. I used aluminium but forgot the dielectric constant of the oxide so it is not just air. Only if I use K=1.41 I am close. Two seperate peases of pcb ? And then there is the edge effect ect. Most formulas I find are aproximations.

I got some standard caps in the range 100-1000 pF but i want to be able to measure it in fF.

Fred PA4TIM

Op 13 jan. 2012 om 15:04 heeft "Poul-Henning Kamp"phk@phk.freebsd.dk het volgende geschreven:

In messageCAE6XXrhydntKXjzq6W8ZA46Fs048CD-Wvrcbotz7kciGd57j5Q@mail.gmail.com
, Will writes:

A Peltier element
is almost as easy to drive as a heater resistor, but dissipated heat
probably makes the thermal design much more challenging.

Actually the major trouble with Peltier is controlling them, because
they are asymetric with respect to transport direction.

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.

Hi Fred: You can not measure a 1 pf cap using a VNA, they are great for measuring things that are near 50 Ohms but the error grows very fast as you move away from 50 Ohms. Check out the error plots in the HP/Agilent Impedance Measurement Handbook for different types of measurement methods. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/Brooke4Congress.html Fred wrote: > Nice Maual. > All you folks, thanks for the info. I have some inspiration. Think I > first try the coaxial approach. But the biggest problem will be to know > the value but a coaxial one is the most easy to measure using a VNA and > that will get me pretty close. > http://www.pa4tim.nl/?p=2929 some pictures and results op to now. > > Fred > > > Brooke Clarke schreef op vr 13-01-2012 om 09:46 [-0800]: >> Hi Fred: >> >> Measuring components is very different from measuring things with connectors. >> In order to get good answers you need to account for stray impedance as well as compensate for things like cable length. >> >> One way to eliminate stray capacitance is to use guarding, for example see: >> http://www.prc68.com/I/HP4274_4275_LCR.shtml#G >> >> For the frequency range where they are available the four terminal pair RLC bridges are by far the most accurate method >> of measuring impedance. >> For more on that and a treasure trove of info on imedance measurements get a copy of the free HP Impedance Measurement >> Handbook and the associated Accessories Selection Guide for Impedance Measurements. Links to those at: >> http://www.prc68.com/I/Z.shtml >> >> For really accurate impedance measurements it's best to use an "analyzer" (sweep frequency test with graphic display) as >> opposed to a "meter" that has a numeric display. The better impedance analyzers have the ability to fit a number of >> models to the measured complex impedance vs frequency plot and give you the circuit values. >> >> For semiconductors their is the HP C-V meter that uses a current source to charge a capacitiance and measures the >> voltage. This data plotted over time gives the semiconductor doping profile. >> >> Have Fun, >> >> Brooke Clarke >> http://www.PRC68.com >> http://www.end2partygovernment.com/Brooke4Congress.html >> >> >> Fred Schneider wrote: >>> I am measuring small capacitances, just for sport but that is more difficult as I thought. >>> I need something that gives a known capacitance around 1 pF. >>> I cut several pieces FR4 in different sizes and measured them several ways, but the problem is the dielectric constant if I use K = 4.5 and distance 1.33 ( it is 1.35 thick form outside copper to outside copper so the 1.33 is also a guess) i get calculated results that are in line with my measurements. Not the same values but the same ratios. >>> >>> I used a digital VNA in shunt mode, a TF1717 bridge from Marconi, the frequency shift methode as described by F.E. terman in RF measurements, a modern LCR meter ( not an expansive very good one) a function generator at 50 KHz and thn measuring the current through the capacitor, an O-opamp plugin with a setup i made to measure small currents ( delta V and delta t are constants so i measure delta i) and the last something call a Capacitance-Frequentie converter i designed, a constant DC current, a constant delta voltage integrator and comprator) and as a result a changing delta T, so frequence is related to capacitance. >>> All measurements are close but not enough ;-) >>> >>> so I need a sturdy standard capacitance. Any suggestions, something using air will be best I think but two metal plates should be straight and mounted solid opposite. I used aluminium but forgot the dielectric constant of the oxide so it is not just air. Only if I use K=1.41 I am close. Two seperate peases of pcb ? And then there is the edge effect ect. Most formulas I find are aproximations. >>> >>> I got some standard caps in the range 100-1000 pF but i want to be able to measure it in fF. >>> >>> Fred PA4TIM >>> >>> >>> >>> >>> >>> Fred PA4TIM >>> >>> Op 13 jan. 2012 om 15:04 heeft "Poul-Henning Kamp"<phk@phk.freebsd.dk> het volgende geschreven: >>> >>>> In message<CAE6XXrhydntKXjzq6W8ZA46Fs048CD-Wvrcbotz7kciGd57j5Q@mail.gmail.com> >>>> , Will writes: >>>> >>>>> A Peltier element >>>>> is almost as easy to drive as a heater resistor, but dissipated heat >>>>> probably makes the thermal design much more challenging. >>>> Actually the major trouble with Peltier is controlling them, because >>>> they are asymetric with respect to transport direction. >>>> >>>> >>>> -- >>>> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >>>> phk@FreeBSD.ORG | TCP/IP since RFC 956 >>>> FreeBSD committer | BSD since 4.3-tahoe >>>> Never attribute to malice what can adequately be explained by incompetence. >>>> >>>> _______________________________________________ >>>> volt-nuts mailing list -- volt-nuts@febo.com >>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >>>> and follow the instructions there. >>> _______________________________________________ >>> volt-nuts mailing list -- volt-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >>> and follow the instructions there. >>> >>> >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > >

PK

Poul-Henning Kamp

Sat, Jan 14, 2012 7:06 AM

In message 1326495142.51960.YahooMailNeo@web161706.mail.bf1.yahoo.com, Randy
Scott writes:

Depends on the temperature difference but I seem to recall that it
is something like 1:3.

Forgive my ignorance, but does this mean that it is "harder" to cool
than it is to heat, given the same magnitude of current through the
junction?

Yes, running electricity through the peltier heats it. The heat is
dissipated evenly throughout.

On the warm side you get:
0.5 * Electrical-heat + Moved-heat

On the cold side you get:
0.5 * Electrical-heat - Moved-heat

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

In message <1326495142.51960.YahooMailNeo@web161706.mail.bf1.yahoo.com>, Randy Scott writes: >>Depends on the temperature difference but I seem to recall that it >>is something like 1:3. > >Forgive my ignorance, but does this mean that it is "harder" to cool >than it is to heat, given the same magnitude of current through the >junction? Yes, running electricity through the peltier heats it. The heat is dissipated evenly throughout. On the warm side you get: 0.5 * Electrical-heat + Moved-heat On the cold side you get: 0.5 * Electrical-heat - Moved-heat -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

ME

Marvin E. Gozum

Tue, Jan 17, 2012 12:11 PM

Some DIY ideas for an environmental chamber. Note, one thing most
don't do is alter relative humidity. To do that you can inject steam.

A key item is getting a chamber big enough for your need. The heat
control is fairly easy to design, many approaches. Cooling to the
40F ish area using a Peltier device is simple solution for a chamber
but its cost efficiency and regulation could be a problem as the cuft
of the chamber grows. I think the heating part is generally easy and
reliable, its getting the right size to save the labor of building
one from scratch, that has both thermal glass, and insulation to build on.

In the eevblog.com post earlier, Dave uses a reptile incubator, there
is a variant sold as a portable cooler/refrigerator under the Coleman
name but the Peltier is set only to cool. The ReptiPro 5000 or its
clones, has reportedly unreliable electronics, either the Peltier or
its thermostat are prone to fail early, but its worth a mod to get a
good sized chamber that has the infrastructure to build both a
heating and cooling chamber in one.

You can find incubators new or eBay that will save you the labor of
building more tightly regulated heat only chambers. Infant animal
incubators, egg incubators and bio-lab incubators are typical search terms.

Toaster or convection ovens work for just heating, and the only value
of changing or supplementing the thermostat is for tighter regulation
and adding a fan to insure the heat is evenly distributed in larger chambers.

If you are lucky to find a used human baby incubator, and have the
room for it, it has both the size, fan, and regulation for good even
heating with portholes for working inside the chamber.

At 06:48 PM 1/13/2012, Bob Smither wrote:

Will wrote:

Varying room temperature is a remarkable source of error when making
measurements in home environment. It would be nice to have a simple
air bath for the items under test. And even better if it was big
enough for the multimeter too. There are commercial units available
but very expensive.

A DIY solution seems to be possible: a simple PI(D) controller built
around an NTC resistor, op-amp, pass-transistor and heater plus a fan
to keep the air moving inside the box. That approach allows
temperature higher than room temperature only but in most cases
stability is important and not the absolute value. A Peltier element
is almost as easy to drive as a heater resistor, but dissipated heat
probably makes the thermal design much more challenging.

I am not an expert and there many questionmarks related air
circulation, thermistor location and probably other things I can't
even imagine.

Hi Will,

For years I have used a modified Rival brand consumer grade
convection oven as a
test chamber. Although I designed it for use up to 200C, it can be
used at any
temperature above ambient.

The oven has a usefully large "cooking" chamber - 16" x 14" x
8.5". The heater
and fan are in a section above the chamber separated by a metal
partition. The
heated air exits that section and enters the chamber through several slots in
the metal partition.

I redid the wiring so that the fan runs all the time and I designed
a simple on
/ off controller to control the heater element. The controller is in series
with the oven bimetallic thermostat which serves as an over temperature safety
cutoff - I just set it well above the temperature I set the controller to.

The controller uses a diode that is placed in the chamber as the sensing
element. A comparator compares the diode voltage to a fixed level
derived from
a reference and a 10 turn pot.

The heater is switched by a solid state relay that is controlled by the
comparator output. The SSR has the nice feature of zero voltage turn on that
reduces any electrical interference.

I have tried different placements of the diode sensor. If it is
located in the
heater / fan section above the chamber the system is very over damped and it
takes a long time to reach equilibrium (the diode "overreacts" to the power
applied to the heater element and shuts down). If it is located in
the chamber,
the oven will overshoot the target temperature as the applied power is not
sensed quickly enough. The best location seems to be in the chamber but close
(~1") to one of the slots where the heated air enters the chamber.

Although the SSR is an on / off device, when close to the set point it behaves
in almost an analog fashion as there is some 60 cycle pickup on the sense lead
(that goes to the diode sensor) so in fact it operates at various
duty cycles as
it applies power to the heater.

I just ran an experiment with three thermocouples in the chamber at different
positions (close to wall, in middle of chamber, ...). The lowest
setting on my
controller is above room temperature at 34C. Here are the minimums
and maximums
through several cycles of the controller at the three different locations as
recorded on a Doric Trendicator 412A:

Position 1: 33.8C - 34.2C
Position 2: 33.7C - 34.2C
Position 3: 33.7C - 34.3C

I have used this oven for over 25 years. Recently the fan motor
finally gave up
but it was easy to replace.

Hope this gives you some ideas.

Bob Smither

Sincerely,

Marv Gozum
Philadelphia, PA

Some DIY ideas for an environmental chamber. Note, one thing most don't do is alter relative humidity. To do that you can inject steam. A key item is getting a chamber big enough for your need. The heat control is fairly easy to design, many approaches. Cooling to the 40F ish area using a Peltier device is simple solution for a chamber but its cost efficiency and regulation could be a problem as the cuft of the chamber grows. I think the heating part is generally easy and reliable, its getting the right size to save the labor of building one from scratch, that has both thermal glass, and insulation to build on. In the eevblog.com post earlier, Dave uses a reptile incubator, there is a variant sold as a portable cooler/refrigerator under the Coleman name but the Peltier is set only to cool. The ReptiPro 5000 or its clones, has reportedly unreliable electronics, either the Peltier or its thermostat are prone to fail early, but its worth a mod to get a good sized chamber that has the infrastructure to build both a heating and cooling chamber in one. You can find incubators new or eBay that will save you the labor of building more tightly regulated heat only chambers. Infant animal incubators, egg incubators and bio-lab incubators are typical search terms. Toaster or convection ovens work for just heating, and the only value of changing or supplementing the thermostat is for tighter regulation and adding a fan to insure the heat is evenly distributed in larger chambers. If you are lucky to find a used human baby incubator, and have the room for it, it has both the size, fan, and regulation for good even heating with portholes for working inside the chamber. At 06:48 PM 1/13/2012, Bob Smither wrote: >Will wrote: > > Varying room temperature is a remarkable source of error when making > > measurements in home environment. It would be nice to have a simple > > air bath for the items under test. And even better if it was big > > enough for the multimeter too. There are commercial units available > > but very expensive. > > > > A DIY solution seems to be possible: a simple PI(D) controller built > > around an NTC resistor, op-amp, pass-transistor and heater plus a fan > > to keep the air moving inside the box. That approach allows > > temperature higher than room temperature only but in most cases > > stability is important and not the absolute value. A Peltier element > > is almost as easy to drive as a heater resistor, but dissipated heat > > probably makes the thermal design much more challenging. > > > > I am not an expert and there many questionmarks related air > > circulation, thermistor location and probably other things I can't > > even imagine. > >Hi Will, > >For years I have used a modified Rival brand consumer grade >convection oven as a >test chamber. Although I designed it for use up to 200C, it can be >used at any >temperature above ambient. > >The oven has a usefully large "cooking" chamber - 16" x 14" x >8.5". The heater >and fan are in a section above the chamber separated by a metal >partition. The >heated air exits that section and enters the chamber through several slots in >the metal partition. > >I redid the wiring so that the fan runs all the time and I designed >a simple on >/ off controller to control the heater element. The controller is in series >with the oven bimetallic thermostat which serves as an over temperature safety >cutoff - I just set it well above the temperature I set the controller to. > >The controller uses a diode that is placed in the chamber as the sensing >element. A comparator compares the diode voltage to a fixed level >derived from >a reference and a 10 turn pot. > >The heater is switched by a solid state relay that is controlled by the >comparator output. The SSR has the nice feature of zero voltage turn on that >reduces any electrical interference. > >I have tried different placements of the diode sensor. If it is >located in the >heater / fan section above the chamber the system is very over damped and it >takes a long time to reach equilibrium (the diode "overreacts" to the power >applied to the heater element and shuts down). If it is located in >the chamber, >the oven will overshoot the target temperature as the applied power is not >sensed quickly enough. The best location seems to be in the chamber but close >(~1") to one of the slots where the heated air enters the chamber. > >Although the SSR is an on / off device, when close to the set point it behaves >in almost an analog fashion as there is some 60 cycle pickup on the sense lead >(that goes to the diode sensor) so in fact it operates at various >duty cycles as >it applies power to the heater. > >I just ran an experiment with three thermocouples in the chamber at different >positions (close to wall, in middle of chamber, ...). The lowest >setting on my >controller is above room temperature at 34C. Here are the minimums >and maximums >through several cycles of the controller at the three different locations as >recorded on a Doric Trendicator 412A: > >Position 1: 33.8C - 34.2C >Position 2: 33.7C - 34.2C >Position 3: 33.7C - 34.3C > >I have used this oven for over 25 years. Recently the fan motor >finally gave up >but it was easy to replace. > >Hope this gives you some ideas. > >Bob Smither Sincerely, Marv Gozum Philadelphia, PA

W

Will

Sat, Jan 21, 2012 2:20 PM

Thanks for the comments. Yesterday I found an old vine cooler / fridge
probably meant for hotel use. Aluminium profile frame and double glass
door, stainless steel inside and outside. The old compressor has been
removed so there is plenty of space for the electronics.

2012/1/17, Marvin E. Gozum marvin.gozum@jefferson.edu:

Some DIY ideas for an environmental chamber. Note, one thing most
don't do is alter relative humidity. To do that you can inject steam.

A key item is getting a chamber big enough for your need. The heat
control is fairly easy to design, many approaches. Cooling to the
40F ish area using a Peltier device is simple solution for a chamber
but its cost efficiency and regulation could be a problem as the cuft
of the chamber grows. I think the heating part is generally easy and
reliable, its getting the right size to save the labor of building
one from scratch, that has both thermal glass, and insulation to build on.

In the eevblog.com post earlier, Dave uses a reptile incubator, there
is a variant sold as a portable cooler/refrigerator under the Coleman
name but the Peltier is set only to cool. The ReptiPro 5000 or its
clones, has reportedly unreliable electronics, either the Peltier or
its thermostat are prone to fail early, but its worth a mod to get a
good sized chamber that has the infrastructure to build both a
heating and cooling chamber in one.

You can find incubators new or eBay that will save you the labor of
building more tightly regulated heat only chambers. Infant animal
incubators, egg incubators and bio-lab incubators are typical search terms.

Toaster or convection ovens work for just heating, and the only value
of changing or supplementing the thermostat is for tighter regulation
and adding a fan to insure the heat is evenly distributed in larger
chambers.

If you are lucky to find a used human baby incubator, and have the
room for it, it has both the size, fan, and regulation for good even
heating with portholes for working inside the chamber.

Thanks for the comments. Yesterday I found an old vine cooler / fridge probably meant for hotel use. Aluminium profile frame and double glass door, stainless steel inside and outside. The old compressor has been removed so there is plenty of space for the electronics. 2012/1/17, Marvin E. Gozum <marvin.gozum@jefferson.edu>: > Some DIY ideas for an environmental chamber. Note, one thing most > don't do is alter relative humidity. To do that you can inject steam. > > A key item is getting a chamber big enough for your need. The heat > control is fairly easy to design, many approaches. Cooling to the > 40F ish area using a Peltier device is simple solution for a chamber > but its cost efficiency and regulation could be a problem as the cuft > of the chamber grows. I think the heating part is generally easy and > reliable, its getting the right size to save the labor of building > one from scratch, that has both thermal glass, and insulation to build on. > > In the eevblog.com post earlier, Dave uses a reptile incubator, there > is a variant sold as a portable cooler/refrigerator under the Coleman > name but the Peltier is set only to cool. The ReptiPro 5000 or its > clones, has reportedly unreliable electronics, either the Peltier or > its thermostat are prone to fail early, but its worth a mod to get a > good sized chamber that has the infrastructure to build both a > heating and cooling chamber in one. > > You can find incubators new or eBay that will save you the labor of > building more tightly regulated heat only chambers. Infant animal > incubators, egg incubators and bio-lab incubators are typical search terms. > > Toaster or convection ovens work for just heating, and the only value > of changing or supplementing the thermostat is for tighter regulation > and adding a fan to insure the heat is evenly distributed in larger > chambers. > > If you are lucky to find a used human baby incubator, and have the > room for it, it has both the size, fan, and regulation for good even > heating with portholes for working inside the chamber.

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DIY Air bath