Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
|
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:
HP-Agilent-Keysight-equipment@groups.io
[mailto: HP-Agilent-Keysight-equipment@groups.io ]
On Behalf Of Jeff Kruth via
Groups.Io
Sent: 22 November 2018 15:38
To: HP-Agilent-Keysight-equipment@groups.io
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:
HP-Agilent-Keysight-equipment@groups.io
[mailto: HP-Agilent-Keysight-equipment@groups.io
] On Behalf Of RFI-EMI-GUY
Sent:
20 November 2018 05:12
To:
HP-Agilent-Keysight-equipment@groups.io
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.
|
Join HP-Agilent-Keysight-equipment@groups.io to automatically receive all group messages.
