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From: John Larkin on 9 Aug 2010 23:00
On Mon, 9 Aug 2010 13:18:18 -0700 (PDT), George Herold
<ggherold(a)gmail.com> wrote:

>On Aug 8, 4:41�pm, John Larkin
><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> On Sat, 7 Aug 2010 13:14:41 -0700 (PDT), George Herold
>>
>>
>>
>>
>>
>> <ggher...(a)gmail.com> wrote:
>> >On Aug 7, 12:12�pm, John Larkin
>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> >> On Thu, 5 Aug 2010 16:39:25 -0700 (PDT), Bret Cahill
>>
>> >> <BretCah...(a)peoplepc.com> wrote:
>> >> >To get to a higher frequency, is it possible to just use a smaller cap
>> >> >and/or resistor on op amp derivative taking circuits?
>>
>> >> What do you mean by "get to a higher frequency"? Do you mean "continue
>> >> to be accurate at a higher signal frequency"?
>>
>> >> The size of the cap scales the constant K in
>>
>> >> OUT = K * (dIN/dt)
>>
>> >> but has nothing to do with how high a frequency the circuit will work
>> >> at. The opamp determines that.
>>
>> >> The "pure" opamp differentiator, just a cap, a resistor, and an opamp,
>> >> seldom works. It tends to be unstable and oscillate.
>>
>> >> Interestingly, its dual, the opamp integrator, has problems of its
>> >> own.
>>
>> >> Do you have any specific performance goals in mind?
>>
>> >> John
>>
>> >What problems do you see with an integrator? �These always seem to
>> >work just fine for me.
>>
>> They integrate their own voltage offset and bias current, of course.
>> For something like a magnetic field probe coil, that gets to be the
>> dominant error. Some cute periodic auto-zero becomes necessary.
>> Chopper amps are great, but noisy.
>>
>> > I find the State Variable filter a bit 'scary'. �Whoever first
>> >thought of putting to integrators in a row had a lot of 'guts'. �But I
>> >love the outcome.
>>
>> We're just finishing up a product that jams 32 brutaly-pipelined
>> 8-pole lowpass filters into one FPGA, sample rate 500 KHz per channel.
>> The cutoff range is 50 KHz down to 1 Hz, and original concept, classic
>> DSP butterfly stages, blew up mathematically. At 1 Hz we had allowable
>> coefficients errors like one part in 10^40, and 2-pole stage gains
>> like 10^17. This wasn't good. I suggested simulating a state-variable
>> lowpass digitally, and that worked, using the 48 bit MACs in the
>> Xilinx FPGA. The nice thing about state-variable filters is that you
>> can make the 2-pole stage gains exactly 1, and the coefficients scale
>> pretty much linearly on frequency.
>>
>" I like SV analog filters, but sometimes a Sallen-Key is better,
> because the DC gain is 1 and doesn't depend on resistor accuracy."
>
>
>I was measuring the DC gain of SV filters we are using a few months
>ago. I was amazed at how accurate they were.
>I can't recall the exact numbers, (My notebooks at work and I'm on
>vacation.) but gain error was much less than the 0.1% resistor
>tolerance.
>They all used the same 10k 0.1% Sumuso (sp) resistors, I guess the
>resistors matched much better than 0.1%. It's hard for me to measure
>things to much better than 0.1%. I need another digit on my
>voltmeter.

Susumu. They are fabulous, come from Digikey, and cost 1/10 of the
Vishay stuff.

>
>Say has anyone looked at the resistor values from 0.1% Sumuso (sp)
>resistors? I wonder if they have the same bimodal
>distribution that was claimed for the old 10% tolerance carbon
>resistors. (where the 5% resistors were selected from the middle of
>the
>normal distribution.) For those who don't know the better Sumuso
>resistors also come in 0.05% tolerance.

The actual available values are bizarre. Maybe they made what specific
customers wanted, then put them on the market. Or used a random number
generator.

We tested some of the 0.05% parts, for TC. We got numbers like 5 and 8
PPM/K.

John

From: George Herold on 10 Aug 2010 10:13
On Aug 9, 11:00 pm, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Mon, 9 Aug 2010 13:18:18 -0700 (PDT), George Herold
>
>
>
>
>
> <ggher...(a)gmail.com> wrote:
> >On Aug 8, 4:41 pm, John Larkin
> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> >> On Sat, 7 Aug 2010 13:14:41 -0700 (PDT), George Herold
>
> >> <ggher...(a)gmail.com> wrote:
> >> >On Aug 7, 12:12 pm, John Larkin
> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> >> >> On Thu, 5 Aug 2010 16:39:25 -0700 (PDT), Bret Cahill
>
> >> >> <BretCah...(a)peoplepc.com> wrote:
> >> >> >To get to a higher frequency, is it possible to just use a smaller cap
> >> >> >and/or resistor on op amp derivative taking circuits?
>
> >> >> What do you mean by "get to a higher frequency"? Do you mean "continue
> >> >> to be accurate at a higher signal frequency"?
>
> >> >> The size of the cap scales the constant K in
>
> >> >> OUT = K * (dIN/dt)
>
> >> >> but has nothing to do with how high a frequency the circuit will work
> >> >> at. The opamp determines that.
>
> >> >> The "pure" opamp differentiator, just a cap, a resistor, and an opamp,
> >> >> seldom works. It tends to be unstable and oscillate.
>
> >> >> Interestingly, its dual, the opamp integrator, has problems of its
> >> >> own.
>
> >> >> Do you have any specific performance goals in mind?
>
> >> >> John
>
> >> >What problems do you see with an integrator?  These always seem to
> >> >work just fine for me.
>
> >> They integrate their own voltage offset and bias current, of course.
> >> For something like a magnetic field probe coil, that gets to be the
> >> dominant error. Some cute periodic auto-zero becomes necessary.
> >> Chopper amps are great, but noisy.
>
> >> > I find the State Variable filter a bit 'scary'.  Whoever first
> >> >thought of putting to integrators in a row had a lot of 'guts'.  But I
> >> >love the outcome.
>
> >> We're just finishing up a product that jams 32 brutaly-pipelined
> >> 8-pole lowpass filters into one FPGA, sample rate 500 KHz per channel.
> >> The cutoff range is 50 KHz down to 1 Hz, and original concept, classic
> >> DSP butterfly stages, blew up mathematically. At 1 Hz we had allowable
> >> coefficients errors like one part in 10^40, and 2-pole stage gains
> >> like 10^17. This wasn't good. I suggested simulating a state-variable
> >> lowpass digitally, and that worked, using the 48 bit MACs in the
> >> Xilinx FPGA. The nice thing about state-variable filters is that you
> >> can make the 2-pole stage gains exactly 1, and the coefficients scale
> >> pretty much linearly on frequency.
>
> >" I like SV analog filters, but sometimes a Sallen-Key is better,
> > because the DC gain is 1 and doesn't depend on resistor accuracy."
>
> >I was measuring the DC gain of SV filters we are using a few months
> >ago.   I was amazed at how accurate they were.
> >I can't recall the exact numbers,  (My notebooks at work and I'm on
> >vacation.)  but gain error was much less than the 0.1% resistor
> >tolerance.
> >They all used the same 10k 0.1% Sumuso (sp) resistors, I guess the
> >resistors matched much better than 0.1%.  It's hard for me to measure
> >things to much better than 0.1%.  I need another digit on my
> >voltmeter.
>
> Susumu. They are fabulous, come from Digikey, and cost 1/10 of the
> Vishay stuff.
>
>
>
> >Say has anyone looked at the resistor values from 0.1% Sumuso (sp)
> >resistors?  I wonder if they have the same bimodal
> >distribution that was claimed for the old 10% tolerance carbon
> >resistors.  (where the 5% resistors were selected from the middle of
> >the
> >normal distribution.)  For those who don't know the better Sumuso
> >resistors also come in 0.05% tolerance.
>
> The actual available values are bizarre. Maybe they made what specific
> customers wanted, then put them on the market. Or used a random number
> generator.
>
> We tested some of the 0.05% parts, for TC. We got numbers like 5 and 8
> PPM/K.
>
> John

Ahh Susumu, Thanks for the correction. I wonder if the 0.1% are
rejects from 0.05% batches. (The 0.1% cost something like 1/5 as
much.) Maybe I'll try and measure some.... Say If I put them in a
bridge I can measure differences with a lot more resolution. Is there
any easy way to swap chip resistors into some test jig? I'll need to
keep the variations in the test jig resistance down below 0.1 ohm or
so.. (for 10k ohm samples).

George H.



From: John Larkin on 10 Aug 2010 20:57
On Tue, 10 Aug 2010 07:13:20 -0700 (PDT), George Herold
<ggherold(a)gmail.com> wrote:

>On Aug 9, 11:00�pm, John Larkin
><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> On Mon, 9 Aug 2010 13:18:18 -0700 (PDT), George Herold
>>
>>
>>
>>
>>
>> <ggher...(a)gmail.com> wrote:
>> >On Aug 8, 4:41�pm, John Larkin
>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> >> On Sat, 7 Aug 2010 13:14:41 -0700 (PDT), George Herold
>>
>> >> <ggher...(a)gmail.com> wrote:
>> >> >On Aug 7, 12:12�pm, John Larkin
>> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> >> >> On Thu, 5 Aug 2010 16:39:25 -0700 (PDT), Bret Cahill
>>
>> >> >> <BretCah...(a)peoplepc.com> wrote:
>> >> >> >To get to a higher frequency, is it possible to just use a smaller cap
>> >> >> >and/or resistor on op amp derivative taking circuits?
>>
>> >> >> What do you mean by "get to a higher frequency"? Do you mean "continue
>> >> >> to be accurate at a higher signal frequency"?
>>
>> >> >> The size of the cap scales the constant K in
>>
>> >> >> OUT = K * (dIN/dt)
>>
>> >> >> but has nothing to do with how high a frequency the circuit will work
>> >> >> at. The opamp determines that.
>>
>> >> >> The "pure" opamp differentiator, just a cap, a resistor, and an opamp,
>> >> >> seldom works. It tends to be unstable and oscillate.
>>
>> >> >> Interestingly, its dual, the opamp integrator, has problems of its
>> >> >> own.
>>
>> >> >> Do you have any specific performance goals in mind?
>>
>> >> >> John
>>
>> >> >What problems do you see with an integrator? �These always seem to
>> >> >work just fine for me.
>>
>> >> They integrate their own voltage offset and bias current, of course.
>> >> For something like a magnetic field probe coil, that gets to be the
>> >> dominant error. Some cute periodic auto-zero becomes necessary.
>> >> Chopper amps are great, but noisy.
>>
>> >> > I find the State Variable filter a bit 'scary'. �Whoever first
>> >> >thought of putting to integrators in a row had a lot of 'guts'. �But I
>> >> >love the outcome.
>>
>> >> We're just finishing up a product that jams 32 brutaly-pipelined
>> >> 8-pole lowpass filters into one FPGA, sample rate 500 KHz per channel.
>> >> The cutoff range is 50 KHz down to 1 Hz, and original concept, classic
>> >> DSP butterfly stages, blew up mathematically. At 1 Hz we had allowable
>> >> coefficients errors like one part in 10^40, and 2-pole stage gains
>> >> like 10^17. This wasn't good. I suggested simulating a state-variable
>> >> lowpass digitally, and that worked, using the 48 bit MACs in the
>> >> Xilinx FPGA. The nice thing about state-variable filters is that you
>> >> can make the 2-pole stage gains exactly 1, and the coefficients scale
>> >> pretty much linearly on frequency.
>>
>> >" I like SV analog filters, but sometimes a Sallen-Key is better,
>> > because the DC gain is 1 and doesn't depend on resistor accuracy."
>>
>> >I was measuring the DC gain of SV filters we are using a few months
>> >ago. � I was amazed at how accurate they were.
>> >I can't recall the exact numbers, �(My notebooks at work and I'm on
>> >vacation.) �but gain error was much less than the 0.1% resistor
>> >tolerance.
>> >They all used the same 10k 0.1% Sumuso (sp) resistors, I guess the
>> >resistors matched much better than 0.1%. �It's hard for me to measure
>> >things to much better than 0.1%. �I need another digit on my
>> >voltmeter.
>>
>> Susumu. They are fabulous, come from Digikey, and cost 1/10 of the
>> Vishay stuff.
>>
>>
>>
>> >Say has anyone looked at the resistor values from 0.1% Sumuso (sp)
>> >resistors? �I wonder if they have the same bimodal
>> >distribution that was claimed for the old 10% tolerance carbon
>> >resistors. �(where the 5% resistors were selected from the middle of
>> >the
>> >normal distribution.) �For those who don't know the better Sumuso
>> >resistors also come in 0.05% tolerance.
>>
>> The actual available values are bizarre. Maybe they made what specific
>> customers wanted, then put them on the market. Or used a random number
>> generator.
>>
>> We tested some of the 0.05% parts, for TC. We got numbers like 5 and 8
>> PPM/K.
>>
>> John
>
>Ahh Susumu, Thanks for the correction. I wonder if the 0.1% are
>rejects from 0.05% batches. (The 0.1% cost something like 1/5 as
>much.) Maybe I'll try and measure some.... Say If I put them in a
>bridge I can measure differences with a lot more resolution. Is there
>any easy way to swap chip resistors into some test jig? I'll need to
>keep the variations in the test jig resistance down below 0.1 ohm or
>so.. (for 10k ohm samples).
>

I think the only fair thing to do is solder them to real surface-mount
pads on a board, especially to measure TC. You never know how stresses
might effect things when you get to single digits of PPMs.

John

From: George Herold on 11 Aug 2010 09:10
On Aug 10, 8:57 pm, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Tue, 10 Aug 2010 07:13:20 -0700 (PDT), George Herold
>
>
>
>
>
> <ggher...(a)gmail.com> wrote:
> >On Aug 9, 11:00 pm, John Larkin
> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> >> On Mon, 9 Aug 2010 13:18:18 -0700 (PDT), George Herold
>
> >> <ggher...(a)gmail.com> wrote:
> >> >On Aug 8, 4:41 pm, John Larkin
> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> >> >> On Sat, 7 Aug 2010 13:14:41 -0700 (PDT), George Herold
>
> >> >> <ggher...(a)gmail.com> wrote:
> >> >> >On Aug 7, 12:12 pm, John Larkin
> >> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> >> >> >> On Thu, 5 Aug 2010 16:39:25 -0700 (PDT), Bret Cahill
>
> >> >> >> <BretCah...(a)peoplepc.com> wrote:
> >> >> >> >To get to a higher frequency, is it possible to just use a smaller cap
> >> >> >> >and/or resistor on op amp derivative taking circuits?
>
> >> >> >> What do you mean by "get to a higher frequency"? Do you mean "continue
> >> >> >> to be accurate at a higher signal frequency"?
>
> >> >> >> The size of the cap scales the constant K in
>
> >> >> >> OUT = K * (dIN/dt)
>
> >> >> >> but has nothing to do with how high a frequency the circuit will work
> >> >> >> at. The opamp determines that.
>
> >> >> >> The "pure" opamp differentiator, just a cap, a resistor, and an opamp,
> >> >> >> seldom works. It tends to be unstable and oscillate.
>
> >> >> >> Interestingly, its dual, the opamp integrator, has problems of its
> >> >> >> own.
>
> >> >> >> Do you have any specific performance goals in mind?
>
> >> >> >> John
>
> >> >> >What problems do you see with an integrator?  These always seem to
> >> >> >work just fine for me.
>
> >> >> They integrate their own voltage offset and bias current, of course..
> >> >> For something like a magnetic field probe coil, that gets to be the
> >> >> dominant error. Some cute periodic auto-zero becomes necessary.
> >> >> Chopper amps are great, but noisy.
>
> >> >> > I find the State Variable filter a bit 'scary'.  Whoever first
> >> >> >thought of putting to integrators in a row had a lot of 'guts'.  But I
> >> >> >love the outcome.
>
> >> >> We're just finishing up a product that jams 32 brutaly-pipelined
> >> >> 8-pole lowpass filters into one FPGA, sample rate 500 KHz per channel.
> >> >> The cutoff range is 50 KHz down to 1 Hz, and original concept, classic
> >> >> DSP butterfly stages, blew up mathematically. At 1 Hz we had allowable
> >> >> coefficients errors like one part in 10^40, and 2-pole stage gains
> >> >> like 10^17. This wasn't good. I suggested simulating a state-variable
> >> >> lowpass digitally, and that worked, using the 48 bit MACs in the
> >> >> Xilinx FPGA. The nice thing about state-variable filters is that you
> >> >> can make the 2-pole stage gains exactly 1, and the coefficients scale
> >> >> pretty much linearly on frequency.
>
> >> >" I like SV analog filters, but sometimes a Sallen-Key is better,
> >> > because the DC gain is 1 and doesn't depend on resistor accuracy."
>
> >> >I was measuring the DC gain of SV filters we are using a few months
> >> >ago.   I was amazed at how accurate they were.
> >> >I can't recall the exact numbers,  (My notebooks at work and I'm on
> >> >vacation.)  but gain error was much less than the 0.1% resistor
> >> >tolerance.
> >> >They all used the same 10k 0.1% Sumuso (sp) resistors, I guess the
> >> >resistors matched much better than 0.1%.  It's hard for me to measure
> >> >things to much better than 0.1%.  I need another digit on my
> >> >voltmeter.
>
> >> Susumu. They are fabulous, come from Digikey, and cost 1/10 of the
> >> Vishay stuff.
>
> >> >Say has anyone looked at the resistor values from 0.1% Sumuso (sp)
> >> >resistors?  I wonder if they have the same bimodal
> >> >distribution that was claimed for the old 10% tolerance carbon
> >> >resistors.  (where the 5% resistors were selected from the middle of
> >> >the
> >> >normal distribution.)  For those who don't know the better Sumuso
> >> >resistors also come in 0.05% tolerance.
>
> >> The actual available values are bizarre. Maybe they made what specific
> >> customers wanted, then put them on the market. Or used a random number
> >> generator.
>
> >> We tested some of the 0.05% parts, for TC. We got numbers like 5 and 8
> >> PPM/K.
>
> >> John
>
> >Ahh Susumu,  Thanks for the correction.  I wonder if the 0.1% are
> >rejects from 0.05% batches.  (The 0.1% cost something like 1/5 as
> >much.)  Maybe I'll try and measure some.... Say If I put them in a
> >bridge I can measure differences with a lot more resolution.  Is there
> >any easy way to swap chip resistors into some test jig?   I'll need to
> >keep the variations in the test jig resistance down below 0.1 ohm or
> >so.. (for 10k ohm samples).
>
> I think the only fair thing to do is solder them to real surface-mount
> pads on a board, especially to measure TC. You never know how stresses
> might effect things when you get to single digits of PPMs.
>
> John

Hmm If I want a quick measure of say 10 or 20 of them that sounds like
a lot of work. Unsoldering surface mount is always a bit of a PITA.
I use solder wick and then push with the iron...

Maybe I could stand the R's on end, solder one end to a PCB and touch
solder a bit of wire to the other end.

The Sumusu data sheet does list TC's at the few ppm level. Resistors
are pretty amazing. What's the TC of a piece of copper?.. one part in
10^4 or something like that. Oh they also sell 0.02% resistors. I
wonder what they cost?

George H.
From: John Larkin on 11 Aug 2010 19:10
On Wed, 11 Aug 2010 06:10:15 -0700 (PDT), George Herold
<ggherold(a)gmail.com> wrote:

>On Aug 10, 8:57�pm, John Larkin
><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> On Tue, 10 Aug 2010 07:13:20 -0700 (PDT), George Herold
>>
>>
>>
>>
>>
>> <ggher...(a)gmail.com> wrote:
>> >On Aug 9, 11:00�pm, John Larkin
>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> >> On Mon, 9 Aug 2010 13:18:18 -0700 (PDT), George Herold
>>
>> >> <ggher...(a)gmail.com> wrote:
>> >> >On Aug 8, 4:41�pm, John Larkin
>> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> >> >> On Sat, 7 Aug 2010 13:14:41 -0700 (PDT), George Herold
>>
>> >> >> <ggher...(a)gmail.com> wrote:
>> >> >> >On Aug 7, 12:12�pm, John Larkin
>> >> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> >> >> >> On Thu, 5 Aug 2010 16:39:25 -0700 (PDT), Bret Cahill
>>
>> >> >> >> <BretCah...(a)peoplepc.com> wrote:
>> >> >> >> >To get to a higher frequency, is it possible to just use a smaller cap
>> >> >> >> >and/or resistor on op amp derivative taking circuits?
>>
>> >> >> >> What do you mean by "get to a higher frequency"? Do you mean "continue
>> >> >> >> to be accurate at a higher signal frequency"?
>>
>> >> >> >> The size of the cap scales the constant K in
>>
>> >> >> >> OUT = K * (dIN/dt)
>>
>> >> >> >> but has nothing to do with how high a frequency the circuit will work
>> >> >> >> at. The opamp determines that.
>>
>> >> >> >> The "pure" opamp differentiator, just a cap, a resistor, and an opamp,
>> >> >> >> seldom works. It tends to be unstable and oscillate.
>>
>> >> >> >> Interestingly, its dual, the opamp integrator, has problems of its
>> >> >> >> own.
>>
>> >> >> >> Do you have any specific performance goals in mind?
>>
>> >> >> >> John
>>
>> >> >> >What problems do you see with an integrator? �These always seem to
>> >> >> >work just fine for me.
>>
>> >> >> They integrate their own voltage offset and bias current, of course.
>> >> >> For something like a magnetic field probe coil, that gets to be the
>> >> >> dominant error. Some cute periodic auto-zero becomes necessary.
>> >> >> Chopper amps are great, but noisy.
>>
>> >> >> > I find the State Variable filter a bit 'scary'. �Whoever first
>> >> >> >thought of putting to integrators in a row had a lot of 'guts'. �But I
>> >> >> >love the outcome.
>>
>> >> >> We're just finishing up a product that jams 32 brutaly-pipelined
>> >> >> 8-pole lowpass filters into one FPGA, sample rate 500 KHz per channel.
>> >> >> The cutoff range is 50 KHz down to 1 Hz, and original concept, classic
>> >> >> DSP butterfly stages, blew up mathematically. At 1 Hz we had allowable
>> >> >> coefficients errors like one part in 10^40, and 2-pole stage gains
>> >> >> like 10^17. This wasn't good. I suggested simulating a state-variable
>> >> >> lowpass digitally, and that worked, using the 48 bit MACs in the
>> >> >> Xilinx FPGA. The nice thing about state-variable filters is that you
>> >> >> can make the 2-pole stage gains exactly 1, and the coefficients scale
>> >> >> pretty much linearly on frequency.
>>
>> >> >" I like SV analog filters, but sometimes a Sallen-Key is better,
>> >> > because the DC gain is 1 and doesn't depend on resistor accuracy."
>>
>> >> >I was measuring the DC gain of SV filters we are using a few months
>> >> >ago. � I was amazed at how accurate they were.
>> >> >I can't recall the exact numbers, �(My notebooks at work and I'm on
>> >> >vacation.) �but gain error was much less than the 0.1% resistor
>> >> >tolerance.
>> >> >They all used the same 10k 0.1% Sumuso (sp) resistors, I guess the
>> >> >resistors matched much better than 0.1%. �It's hard for me to measure
>> >> >things to much better than 0.1%. �I need another digit on my
>> >> >voltmeter.
>>
>> >> Susumu. They are fabulous, come from Digikey, and cost 1/10 of the
>> >> Vishay stuff.
>>
>> >> >Say has anyone looked at the resistor values from 0.1% Sumuso (sp)
>> >> >resistors? �I wonder if they have the same bimodal
>> >> >distribution that was claimed for the old 10% tolerance carbon
>> >> >resistors. �(where the 5% resistors were selected from the middle of
>> >> >the
>> >> >normal distribution.) �For those who don't know the better Sumuso
>> >> >resistors also come in 0.05% tolerance.
>>
>> >> The actual available values are bizarre. Maybe they made what specific
>> >> customers wanted, then put them on the market. Or used a random number
>> >> generator.
>>
>> >> We tested some of the 0.05% parts, for TC. We got numbers like 5 and 8
>> >> PPM/K.
>>
>> >> John
>>
>> >Ahh Susumu, �Thanks for the correction. �I wonder if the 0.1% are
>> >rejects from 0.05% batches. �(The 0.1% cost something like 1/5 as
>> >much.) �Maybe I'll try and measure some.... Say If I put them in a
>> >bridge I can measure differences with a lot more resolution. �Is there
>> >any easy way to swap chip resistors into some test jig? � I'll need to
>> >keep the variations in the test jig resistance down below 0.1 ohm or
>> >so.. (for 10k ohm samples).
>>
>> I think the only fair thing to do is solder them to real surface-mount
>> pads on a board, especially to measure TC. You never know how stresses
>> might effect things when you get to single digits of PPMs.
>>
>> John
>
>Hmm If I want a quick measure of say 10 or 20 of them that sounds like
>a lot of work. Unsoldering surface mount is always a bit of a PITA.
>I use solder wick and then push with the iron...
>
>Maybe I could stand the R's on end, solder one end to a PCB and touch
>solder a bit of wire to the other end.
>
>The Sumusu data sheet does list TC's at the few ppm level. Resistors
>are pretty amazing. What's the TC of a piece of copper?.. one part in
>10^4 or something like that.


Much worse, around 0.4% per K. Most metals are in that ballpark.

John

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