EDN garbage?

[George Herold]

I was browsing EDN. Is this guy full of it?

http://www.edn.com/electronics-blogs/living-analog/4406272/Thermoelectric-gradients

Thanks,

George H.

 

[Tim Wescott]

On Tue, 05 Feb 2013 13:10:32 -0800, George Herold wrote:

I was browsing EDN. Is this guy full of it?

http://www.edn.com/electronics-blogs/living-analog/4406272/
Thermoelectric-gradients

Only in that he doesn't quantify how great the effect is. One thing I've
learned about metrology is that _everything_ affects your measurements --
it's just that some things don't affect your measurements as much as
others. Did you look at the paper he referenced? Did it quantify things
at all?

So I've learned not to discount any effect when I'm trying to take a
measurement to finer accuracy than I ever had before, or in the presence
of greater disturbing effects than ever before, etc.

And I've learned to review all possible effects when I'm trying to take a
measurement that I _have_ taken successfully before, but can't now.

The key is knowing which thing to look at first, which, since I'm not a
metrology expert, I often get wrong.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

 

[George Herold]

On Feb 5, 7:39 pm, Tim Wescott <t...@seemywebsite.com> wrote:

On Tue, 05 Feb 2013 13:10:32 -0800, George Herold wrote:
I was browsing EDN.  Is this guy full of it?

http://www.edn.com/electronics-blogs/living-analog/4406272/

Thermoelectric-gradients

Only in that he doesn't quantify how great the effect is.  One thing I've
learned about metrology is that _everything_ affects your measurements --
it's just that some things don't affect your measurements as much as
others.  Did you look at the paper he referenced?

I browsed the referedd to paper.. I didn't find anything about the
gradients along the wire.... I assume it says something to the same
effect somewhere.

To be honest the thermo-electric effect has always been a bit
mysterious to me. But I never heard of thermal gradients along the
wire making a difference. I guess maybe if you try and draw too much
current from the TC jucntion.


Did it quantify things

at all?

Yeah show me some numbers! Do a measurement.
I saw none of that.

Sorry for wasting both our times.

George H.

So I've learned not to discount any effect when I'm trying to take a
measurement to finer accuracy than I ever had before, or in the presence
of greater disturbing effects than ever before, etc.

And I've learned to review all possible effects when I'm trying to take a
measurement that I _have_ taken successfully before, but can't now.

The key is knowing which thing to look at first, which, since I'm not a
metrology expert, I often get wrong.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com

 

[Phil Hobbs]

On 2/5/2013 4:10 PM, George Herold wrote:

I was browsing EDN. Is this guy full of it?

http://www.edn.com/electronics-blogs/living-analog/4406272/Thermoelectric-gradients

Yes, he's full of it, assuming that the thermocouple wires are really of
uniform composition along their length, and that the ends of the leads
(where the amp is connected) are at the same temperature. In general a
thermocouple measurement system has a bunch of thermocouple junctions,
most of which we want to be able to ignore--e.g. the terminal to the PC
trace, trace to pin, pin to wirebond, wirebond to chip wiring, chip
wiring to silicon...and back again.

Thermocouples stink for uses near room temperature.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net

 

[George Herold]

On Feb 5, 11:41 pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:

On 2/5/2013 4:10 PM, George Herold wrote:

I was browsing EDN.  Is this guy full of it?

http://www.edn.com/electronics-blogs/living-analog/4406272/Thermoelec...

Yes, he's full of it, assuming that the thermocouple wires are really of
uniform composition along their length, and that the ends of the leads
(where the amp is connected) are at the same temperature.  In general a
thermocouple measurement system has a bunch of thermocouple junctions,
most of which we want to be able to ignore--e.g. the terminal to the PC
trace, trace to pin, pin to wirebond, wirebond to chip wiring, chip
wiring to silicon...and back again.

Yup, thanks

Thermocouples stink for uses near room temperature.

Oh, now you tell me. :^)
I use copper-constantan TC as 'mostly' non-magnetic sensors. (fairly
fine gauge wire.) I'm not sure what other sensors would be non-
magnetic.
Maybe a little SMD diode? The TC's are very convenient though... just
stuff the wire where you want to measure. And cheap OTS
conttrollers.

George H.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot nethttp://electrooptical.net

 

[Phil Hobbs]

On 2/6/2013 4:06 PM, George Herold wrote:

On Feb 5, 11:41 pm, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net> wrote:
On 2/5/2013 4:10 PM, George Herold wrote:

I was browsing EDN. Is this guy full of it?

http://www.edn.com/electronics-blogs/living-analog/4406272/Thermoelec...

Yes, he's full of it, assuming that the thermocouple wires are really of
uniform composition along their length, and that the ends of the leads
(where the amp is connected) are at the same temperature. In general a
thermocouple measurement system has a bunch of thermocouple junctions,
most of which we want to be able to ignore--e.g. the terminal to the PC
trace, trace to pin, pin to wirebond, wirebond to chip wiring, chip
wiring to silicon...and back again.

Yup, thanks

Thermocouples stink for uses near room temperature.

Oh, now you tell me. :^)
I use copper-constantan TC as 'mostly' non-magnetic sensors. (fairly
fine gauge wire.) I'm not sure what other sensors would be non-
magnetic.
Maybe a little SMD diode? The TC's are very convenient though... just
stuff the wire where you want to measure. And cheap OTS
conttrollers.

Yeah, well, thermocouples are a bit of a hobby horse of mine, as you know.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Tue, 5 Feb 2013 13:10:32 -0800 (PST), George Herold <gherold@teachspin.com>
wrote:

I was browsing EDN. Is this guy full of it?

http://www.edn.com/electronics-blogs/living-analog/4406272/Thermoelectric-gradients

Thanks,

George H.

Oh, EDN has been garbage for years now. Fortunately, it's getting thinner and
thinner and should disappear entirely soon.

The author is an idiot. The voltage gradient that he refers to isn't an error,
it *is* the signal.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[whit3rd]

On Tuesday, February 5, 2013 1:10:32 PM UTC-8, George Herold wrote:

I was browsing EDN. Is this guy full of it?

http://www.edn.com/electronics-blogs/living-analog/4406272/Thermoelectric-gradients

[calling the temperature gradients in wire an error source]

Well, the gradients are NOT an error source, but you'll
never convince him, because he can show you a counterexample.
Take a length of soft iron wire (sacrifice a coathanger, if you have to).
Connect the ends to an ammeter.
You'll see zero circuit current. Now fire up a torch and heat the wire
to make a hot spot. Still zero circuit current. Now slowly move the
hot spot.

When the hot spot in the wire goes one way, the current turns negative. Move
it the other way, the current goes positive.

The temperature gradient in the wire DOES make a thermocouple net voltage
here, because your hot spot is a different allotrope (sometimes called Austenite)
of iron crystal than the cold wire is. The Austenite-Martensite transition at
the trailing edge of your moving hot spot occurs at lower temperature than
the transition at the leading edge, because the transition has hysteresis. The
iron wire is thus two different metals, with connections at different temperatures.

So, if the thermocouple materials undergo phase transitions, the gradients
in the connecting wire do have a net effect on the circuit. That's a good argument
for knowing a LOT about the thermocouple wire materials before you measure
with them.

 

[Cydrome Leader]

George Herold <gherold@teachspin.com> wrote:

I was browsing EDN. Is this guy full of it?

http://www.edn.com/electronics-blogs/living-analog/4406272/Thermoelectric-gradients

Thanks,

George H.

it looks like a copied rehash of the video recently posted to eevblog.com
about thermocouple wires.