|
General Microwave used to make thinfilm 50 ohm thermocouples for their power meter sensors. I don’t know if they are in business any more. Regards, John Burgar ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of RFI-EMI-GUY
Sent: Monday, November 19, 2018 1:42 PM
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters ? Is there any other company on the planet who produces 50 OHM thermocouples? It seems odd that such a thing is unobtainable.
|
I have such an animal here a GM 460B with that TFT hermocouple. It is an ancient beast. They got bought up by Marconi down the line.
https://patents.google.com/patent/US3384819
|
Are these thermocouples or thermistors?
These are different.
Glenn
WB4UIV
On 11/19/2018 11:45 PM, John E. Burgar
wrote:
General
Microwave used to make thinfilm 50 ohm thermocouples for
their power meter sensors. I don’t know if they are in
business any more. Regards, John Burgar
?
From:
[email protected]
[mailto:[email protected]] On
Behalf Of RFI-EMI-GUY
Sent: Monday, November 19, 2018 1:42 PM
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Issue
with homemade diode power sensor for HP meters
?
Is there any other company on the planet
who produces 50 OHM thermocouples? It seems odd that such a
thing is unobtainable.
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
|
Hi
What are frequently called RF thermocouples are in fact three or four terminal devices with a heating element (50 Ohm or 75 Ohm resistance) with an embedded thermocouple.
73 George G6HIG
On Tuesday, November 20, 2018 12:42 PM, Glenn Little <glennmaillist@...> wrote:
Are these thermocouples or thermistors?
These are different.
Glenn
WB4UIV
On 11/19/2018 11:45 PM, John E. Burgar
wrote:
General
Microwave used to make thinfilm 50 ohm thermocouples for
their power meter sensors. I don’t know if they are in
business any more. Regards, John Burgar
?
?
Is there any other company on the planet
who produces 50 OHM thermocouples? It seems odd that such a
thing is unobtainable.
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
|
Thermocouples with an embeded 50 ohm resistor..The 50 ohm resistor is the heater and thermocouple generates a voltage
proportional to the heat gnerated in the resistor
Dave
manuals@...
toggle quoted message
Show quoted text
On 11/20/2018 7:41 AM, Glenn Little wrote: Are these thermocouples or thermistors?
These are different.
Glenn
WB4UIV
On 11/19/2018 11:45 PM, John E. Burgar wrote:
General Microwave used to make thinfilm 50 ohm thermocouples for their power meter sensors. I don’t know if they are in business any more. Regards, John Burgar
*From:*[email protected] [mailto:[email protected]] *On Behalf Of *RFI-EMI-GUY
*Sent:* Monday, November 19, 2018 1:42 PM
*To:* [email protected]
*Subject:* Re: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
Is there any other company on the planet who produces 50 OHM thermocouples? It seems odd that such a thing is unobtainable.
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIVwb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
--
Dave
Manuals@...
www.ArtekManuals.com
|
Do you know the thermocouple type? And the resistor power rating?
I’m just wondering if it might be possible to solder a micro thermocouple to a extra small surface mount resistor.
Peter
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Show quoted text
On Nov 20, 2018, at 9:12 AM, Artekmedia <manuals@...> wrote:
Thermocouples with an embeded 50 ohm resistor..The 50 ohm resistor is the heater and thermocouple generates a voltage
proportional to the heat gnerated in the resistor
Dave
manuals@...
On 11/20/2018 7:41 AM, Glenn Little wrote:
Are these thermocouples or thermistors?
These are different.
Glenn
WB4UIV
On 11/19/2018 11:45 PM, John E. Burgar wrote:
General Microwave used to make thinfilm 50 ohm thermocouples for their power meter sensors. I don’t know if they are in business any more. Regards, John Burgar
*From:*[email protected] [mailto:[email protected]] *On Behalf Of *RFI-EMI-GUY
*Sent:* Monday, November 19, 2018 1:42 PM
*To:* [email protected]
*Subject:* Re: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
Is there any other company on the planet who produces 50 OHM thermocouples? It seems odd that such a thing is unobtainable.
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIVwb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license" --
Dave
Manuals@...
www.ArtekManuals.com
|
Peter,
it seems to be possible. This is exactly what this guy has done:
(This type of sensor is also known as Bolometer, apparently.)
However, I would not expect a terribly good accuracy.
To get rid of the ambient temperature impact, two resistors can be used where the one of the resistors is always kept, say, 30K hotter than the other. This way the ambient temperature cancels out.
|
A bolometer is not a thermocouple sensor. What it is is a
small lightbulb filament in a vacuum that is exposed to the
RF power. When the filament starts to heat up, its electrical
resistance starts to rise in a way that is related to its
exposed power level.
If I recall correctly, Bolometers were used in a bridge circuit,
where you applied AC power, and the bridge measured the resistance
of the filament. Next, you applied DC power, increasing the
level until the resistance measured by the bridge matched that of
the unknown RF power source. At that point, the DC power was equal
to the unknown RF power source's power.
-Chuck Harris
Tobias Pluess wrote:
toggle quoted message
Show quoted text
Peter,
it seems to be possible. This is exactly what this guy has done:
(This type of sensor is also known as Bolometer, apparently.)
However, I would not expect a terribly good accuracy.
To get rid of the ambient temperature impact, two resistors can be used where the one of the resistors is always kept, say, 30K hotter than the other. This way the ambient temperature cancels out.
|
Chuck and others, No doubt you are right about the small light bulb been used: Here is my memory from EE school: In ancient times, the 1960’s (if I remember right) a bolometer system was implemented with a common low current fuse. It was arranged in a bridge circuit of sorts: It’s resistance was adjusted with DC current by a “zero setting” arrangement to get zero indication on a meter. Then when RF power was applied, the bridge/feedback circuit automatically rebalanced the thing back to the resistance set earlier - the reduction in (dc?) power drove the indicator to show the RF power that was being applied. One advantage of this scheme is that the unavoidable non-linearities in the bolometer fuse did not affect the measurement, since the bolometer was returned to its initial resistance/dissipation condition. This basic scheme of “first set null balance, and then return the bridge to null when the unknown is introduced” was used throughout General Radio bridges of all sorts. I would expect the GR instruments to include a bloomer-based power indicator, though I am not familiar with it/them. One (or more) of the MIT Radiation Lab series of books covers this topic, and quite thoroughly. I have a small group of those books “in storage” here and can look among them before the temperature goes too far below freezing. But see below for an online example of Volume 11. Likely one of these covers the topic: 8. Principles of microwave circuits - Montgomery, C. G.; Purcell, E. M. and Dicke, R. H. (1948) 11. Technique of microwave measurements - Montgomery, C. G. (1947) (It appears that my list of the RadLab books came from: This link no longer works but: Does and I did get volume 11 from there. At MIT, I find a page about the series, but not the texts of the volumes: ) In the second above, page 81 mention is made of “bolometers”, being implemented with thermistors and bolometer, these having negative and positive temperature coefficients. It goes on to describe bridge circuits and the characteristics of the measurement elements. Roy On Nov 20, 2018, at 10:20 AM, Chuck Harris <cfharris@...> wrote:
A bolometer is not a thermocouple sensor. What it is is a
small lightbulb filament in a vacuum that is exposed to the
RF power. ...
If I recall correctly, Bolometers were used in a bridge circuit,
where you applied AC power, and the bridge measured the resistance
of the filament. Next, you applied DC power, increasing the
level until the resistance measured by the bridge matched that of
the unknown RF power source. At that point, the DC power was equal
to the unknown RF power source's power.
-Chuck Harris Roy Morgan K1LKY since 1958 k1lky68@...
|
Ham Radio magazine (Dec. '77) had an article on building a "bolo-meter" type rf power meter ...Used small light bulbs in the sensor . I found a few pilot lights from old cb's that had the right resistance curve ... Also in April '86 an article using a "zero bias hot carrier diode"? chopper stabilized (with relays)
Jim
On Wednesday, November 21, 2018, 7:18:10 AM PST, Roy Morgan <k1lky68@...> wrote:
Chuck and others,
No doubt you are right about the small light bulb been used:? Here is my memory from EE school:
In ancient times, the 1960’s (if I remember right) a bolometer system was implemented with a common low current fuse.? It was arranged in a bridge circuit of sorts: It’s resistance was adjusted with DC current by a “zero setting” arrangement to get zero indication on a meter.? Then when RF power was applied, the bridge/feedback circuit automatically rebalanced the thing back to the resistance set earlier - the reduction in (dc?) power drove the indicator to show the RF power that was being applied.
One advantage of this scheme is that the unavoidable non-linearities in the bolometer fuse did not affect the measurement, since the bolometer was returned to its initial resistance/dissipation condition.? This basic scheme of “first set null balance, and then return the bridge to null when the unknown is introduced” was used throughout General Radio bridges of all sorts.? I would expect the GR instruments to include a bloomer-based power indicator, though I am not familiar with it/them.
One (or more) of the MIT Radiation Lab series of books covers this topic, and quite thoroughly.? I have a small group of those books “in storage” here and can look among them before the temperature goes too far below freezing.? But see below for an online example of Volume 11.
Likely one of these covers the topic:
8. Principles of microwave circuits - Montgomery, C. G.; Purcell, E. M. and Dicke, R. H. (1948)
11. Technique of microwave measurements - Montgomery, C. G. (1947)
(It appears that my list of the RadLab books came from:
This link no longer works but:
Does and I did get volume 11 from there.
At MIT, I find a page about the series, but not the texts of the volumes:
)
In the second above, page 81 mention is made of “bolometers”, being implemented with thermistors and bolometer, these having negative and positive temperature coefficients.? It goes on to describe bridge circuits and the characteristics of the measurement elements.
Roy
> On Nov 20, 2018, at 10:20 AM, Chuck Harris < cfharris@...> wrote: >
> A bolometer is not a thermocouple sensor.? What it is is a
> small lightbulb filament in a vacuum that is exposed to the
> RF power. ...
> If I recall correctly, Bolometers were used in a bridge circuit,
> where you applied AC power, and the bridge measured the resistance
> of the filament.? Next, you applied DC power, increasing the
> level until the resistance measured by the bridge matched that of
> the unknown RF power source.? At that point, the DC power was equal
> to the unknown RF power source's power.
>
> -Chuck Harris
Roy Morgan
K1LKY since 1958
|
(It appears that my list of the RadLab books came from:
This link no longer works but:
Does and I did get volume 11 from there.
At MIT, I find a page about the series, but not the texts of the volumes:
)
In the second above, page 81 mention is made of “bolometers”, being
implemented with thermistors and bolometer, these having negative and
positive temperature coefficients. It goes on to describe bridge circuits and
the characteristics of the measurement elements. There's a copy of the Rad Lab series on ko4bb.com: -- john, KE5FX
|
The GM / Marconi TfT deivces are thermocouple arrays. Bismuth /nichrome couples bad as a electrical generation device but can be made to match 50R. The resistor thermocouple types were common in RF ammeters and some power meters. The early?Marconi TF144 signal generator models used them for the output meter. The classic thermistor detector is the HP 478A that was first used?with the 431A power meter around 1961 and still made today at $5000 a pop. The analogue ?432B power meter was discontinued a few years ago with a final price of over $10,000 but the pair can be picked up for a few hundred dollars used. They built a new digital meter for the 478A the N432A at $10,000. but none if these appear in the Keysight power meter guide tables. So why is this "old tech" still made? the answer is in the guide: "Not discussed is the Keysight family of thermistor sensors and the associated Keysight 432A power meter. This venerable technology now is used almost exclusively for the standardization and traceability of power measurements from the U.S. National Institute of Standards and Technology and other international standards agencies. Because the Keysight 432A power meter and thermistor sensor technology is based on the highly precise DC-substitution method, the sensors are used as transfer standards, traveling between the user’s primary lab and the NIST measurement services laboratory. Users interested in such metrology power-transfer processes may request Keysight’s AN 64-1, 5965-6630E and AN 64-4, 5965-8167E application notes." Basically you can use a head with any 431/432/N432 meter and a accurate DC?DVM to get transfer accuracy to?a national standard. The "meter" is just a servo to balance the bridge and the accuracy is at the DC voltage. They do special variants of the head?with larger blocking capacitors for low frequency work. ? Robert G8RPI.
?
|
Thanks for the Rad Lab link. It appears that all the volumes are available in PDF format. I'm downloading them all now. Having read a history of the Rad Lab and a biography of the man responsible, Alfred Loomis, it should be a lot of fun to read.
For those not aware of it, the Rad Lab existed in Tuxedo Park, NY as a personal project of Alfred Loomis before WW II. Loomis was also involved in building the cyclotron at Berkeley. Lui Alvarez made an off hand comment to Loomis one evening that if they couldn't get copper they could use aluminum. Alvarez was blow away the next morning when Loomis told him it was not possible to build the magnets with aluminum wire for any of the designs being discussed. Loomis had stayed up all night making the calculations.
Loomis invented LORAN in the shower after a conversation with a Brit who was visiting. They wanted to name it after him, but he declined so they came up with a phrase to match the acronym.
Loomis closed the Rad Lab at the end of the war because he didn't think the government should be involved in research except in exigent circumstances such as war.
|
Regarding the TFT ?Marconi?
power meter ?they had 2? thermisters? at 100 ohm each
?And connected so that DC they added up
to 200 ohm but presented a 50? to an AC signal
?
The power sensor was easily tested as the
2 large pins on the convector should read 200 ohm
?
?
I have such an animal here a GM 460B with that TFT hermocouple. It is
an ancient beast. They got bought up by Marconi down the line.
https://patents.google.com/patent/US3384819
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Hi regarding the HP power meters
HP 430?? was the first of the
microwave power meters ?its coaxial thermistor mount HP
477 ?10 mhz to 10 Ghz?
The HP 430 sold for $300? in 1967??
and? the ?HP 477 sold for $75? in 1967??
I did all my early microwave experiments
with the? 430 ?and then progressed onto a 431
?
The improved system using a second thermistor
in the coaxial thermistor mount for temperature compensation HP 431 ?&
HP 478 and a wider dynamic range
The HP 431 sold for $475? in 1967??
and? the ?HP 478 sold for $155? in 1967??
?
Currently looking for wave guide power sensors
above 50 ghz
?
Regards Paul B?
?
From:
[email protected]
[mailto:[email protected]]
On Behalf Of Robert G8RPI via
Groups.Io
Sent: 22 November 2018 07:52
To: [email protected]
Subject: Re: 50 ohm thermocouples
was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor
for HP meters
?
The GM / Marconi TfT deivces are thermocouple arrays. Bismuth /nichrome
couples bad as a electrical generation device but can be made to match 50R.
The resistor thermocouple types were common in RF ammeters and some power
meters. The early?Marconi TF144 signal generator models used them for the
output meter.
The classic thermistor detector is the HP 478A that was first used?with
the 431A power meter around 1961 and still made today at $5000 a pop. The
analogue ?432B power meter was discontinued a few years ago with a final
price of over $10,000 but the pair can be picked up for a few hundred dollars
used. They built a new digital meter for the 478A the N432A at $10,000. but
none if these appear in the Keysight power meter guide tables.
So why is this "old tech" still made? the answer is in the guide:
"Not discussed is the Keysight family of thermistor sensors and the
associated Keysight 432A power meter. This venerable technology now is used
almost exclusively for the
standardization and traceability of power measurements from the U.S. National
Institute of Standards and Technology and other international standards
agencies. Because the Keysight 432A power meter and thermistor sensor
technology is based on the highly precise DC-substitution method, the sensors
are used as transfer standards, traveling between the user’s primary lab
and the NIST measurement services laboratory.
Users interested in such metrology power-transfer processes may request
Keysight’s AN 64-1, 5965-6630E and AN 64-4, 5965-8167E application
notes."
Basically you can use a head with any 431/432/N432 meter and a accurate
DC?DVM to get transfer accuracy to?a national standard. The
"meter" is just a servo to balance the bridge and the accuracy is at
the DC voltage. They do special variants of the head?with larger blocking
capacitors for low frequency work.
?
Robert G8RPI.
?
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
On 11/22/18 1:51 AM, Robert G8RPI via Groups.Io wrote: Because the Keysight 432A power meter and thermistor sensor technology is based on the highly precise DC-substitution method, the sensors are used as transfer standards, traveling between the user’s primary lab and the NIST measurement services laboratory. Are the diode sensors for lower levels good and linear so a transfer from a 432A sensor gives a good cal on the nanowatt ranges?
|
The reference is "Tuxedo Park" by Jennet Conant, a marvelous book! I use this as well as others when I talk about electrotechnology and the importance of WWII to my students.? However the facts as presented were incomplete/incorrect.
For those not aware of it, the Rad Lab existed in Tuxedo Park, NY as a personal project of Alfred Loomis before WW II.?
No. Loomis, made rich by the electrification of America, pulled out of the stock market before the crash and used part of his considerable fortune to establish a personal research lab in a mansion purchased from a now-broke millionaire, so that he could pursue his true love: science.
Loomis was also involved in building the cyclotron at Berkeley.?Yes, He was friends with Lawrence and funded him.
Luis Alvarez made an off hand comment to Loomis one evening that if they couldn't get copper they could use aluminum.? Alvarez was blow away the next morning when Loomis told him it was not possible to build the magnets with aluminum wire for any of the designs being discussed.? Loomis had stayed up all night making the calculations.
No, it was a few days later, and the reason was that the cost savings was not sufficient to justify the increased size. (pp 143-144 in "Tuxedo Park").
Loomis invented LORAN in the shower after a conversation with a Brit who was visiting.? They wanted to name it after him, but he declined so they came up with a phrase to match the acronym.? Bowen had given Loomis the patents for Gee, the British system, which he adapted to a longer wave system. He did add the master/slave idea.
Loomis closed the Rad Lab at the end of the war because he didn't think the government should be involved in research except in exigent circumstances such as war.
Loomis closed his personal lab at Tuxedo Park after he moved to MIT to help run the Rad Lab there. He never re-opened it after the war, he had moved on.? His personal lab did research long before the war. He never sought fame, only putting his name on the first patent in a field, like ultrasonics, or brain wave research. He left the follow-up work for others. He did not have any misgivings about the govt in research.
|
Really? Because HP used the same idea in the 478A & 8478A heads, they were 200 ohms series under AC bias, 50 ohms to RF, but when measured "cold" with an ohm-meter they were approx 3-4K ohms. I would have thought G-M would have used a similar method.
The big thing with the HP heads was the balance between the ref thermistor pair and the measurement thermistor pair. If the measurement pair was damaged by excess RF power, the "rest" resistance was too different from the temperature reference pair (say 7K instead of 4 K). SO you could no longer balance them with the screws.
J.Kruth
In a message dated 11/22/2018 9:29:03 AM Eastern Standard Time, paul@... writes:
Regarding the TFT ?Marconi? power meter ?they had 2? thermisters? at 100 ohm each
?And connected so that DC they added up to 200 ohm but presented a 50? to an AC signal
?
The power sensor was easily tested as the 2 large pins on the convector should read 200 ohm
?
From: [email protected] [mailto: [email protected] ] On Behalf Of RFI-EMI-GUY
Sent: 20 November 2018 05:12
To: [email protected]
Subject: Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
?
I have such an animal here a GM 460B with that TFT hermocouple. It is an ancient beast. They got bought up by Marconi down the line.
https://patents.google.com/patent/US3384819
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Hi Jeff??
good to talk to you again regarding the 478
and rebalancing the head using the screws
I have found that the temperature? compensation
isn’t as good after you have to rebalance using the screws
?
By the way never opened the 478? to
find out how the screws work
Paul B
?
From:
[email protected]
[mailto:[email protected]]
On Behalf Of Jeff Kruth via
Groups.Io
Sent: 22 November 2018 15:38
To: [email protected]
Subject: Re: 50 ohm thermocouples
was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor
for HP meters
?
Really? Because HP used
the same idea in the 478A & 8478A heads, they were 200 ohms series under AC
bias, 50 ohms to RF, but when measured "cold" with an ohm-meter they
were approx 3-4K ohms. I would have thought G-M would have used a similar
method.
The big thing with the
HP heads was the balance between the ref thermistor pair and the measurement
thermistor pair. If the measurement pair was damaged by excess RF power, the
"rest" resistance was too different from the temperature reference
pair (say 7K instead of 4 K). SO you could no longer balance them with the
screws.
In a message dated 11/22/2018 9:29:03 AM Eastern Standard Time,
paul@... writes:
Regarding the TFT
?Marconi? power meter ?they had 2? thermisters? at 100
ohm each
?And connected so
that DC they added up to 200 ohm but presented a 50? to an AC signal
?
The power sensor was
easily tested as the 2 large pins on the convector should read 200 ohm
?
From:
[email protected]
[mailto: [email protected]
] On Behalf Of RFI-EMI-GUY
Sent:
20 November 2018 05:12
To:
[email protected]
Subject:
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with
homemade diode power sensor for HP meters
?
I have such an animal here a GM 460B with that TFT
hermocouple. It is an ancient beast. They got bought up by Marconi down the
line.
https://patents.google.com/patent/US3384819
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
Interesting point. I have not worked with thermistor heads since ages but I always wondered how the screws work on the HP478 and HP8478? 73 de
Harke
On Thursday, November 22, 2018, 4:58:38 PM GMT+1, Paul Bicknell <paul@...> wrote:
Hi Jeff??
good to talk to you again regarding the 478
and rebalancing the head using the screws
I have found that the temperature? compensation
isn’t as good after you have to rebalance using the screws
?
By the way never opened the 478? to
find out how the screws work
Paul B
?
From:
[email protected]
[mailto: [email protected] ]
On Behalf Of Jeff Kruth via
Groups.Io
Sent: 22 November 2018 15:38
To: [email protected]
Subject: Re: 50 ohm thermocouples
was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor
for HP meters
?
Really? Because HP used
the same idea in the 478A & 8478A heads, they were 200 ohms series under AC
bias, 50 ohms to RF, but when measured "cold" with an ohm-meter they
were approx 3-4K ohms. I would have thought G-M would have used a similar
method.
The big thing with the
HP heads was the balance between the ref thermistor pair and the measurement
thermistor pair. If the measurement pair was damaged by excess RF power, the
"rest" resistance was too different from the temperature reference
pair (say 7K instead of 4 K). SO you could no longer balance them with the
screws.
In a message dated 11/22/2018 9:29:03 AM Eastern Standard Time,
paul@... writes:
Regarding the TFT
?Marconi? power meter ?they had 2? thermisters? at 100
ohm each
?And connected so
that DC they added up to 200 ohm but presented a 50? to an AC signal
?
The power sensor was
easily tested as the 2 large pins on the convector should read 200 ohm
?
From:
[email protected]
[mailto: [email protected]
] On Behalf Of RFI-EMI-GUY
Sent:
20 November 2018 05:12
To:
[email protected]
Subject:
Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with
homemade diode power sensor for HP meters
?
I have such an animal here a GM 460B with that TFT
hermocouple. It is an ancient beast. They got bought up by Marconi down the
line.
https://patents.google.com/patent/US3384819
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
No virus found in this message.
Checked by AVG -
Version: 2016.0.8048 / Virus Database: 4793/15883 - Release Date: 08/14/18
Internal Virus Database is out of date.
|
RFI-EMI-GUY
jim
Paul Bicknell