Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
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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
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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
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