Re: 50 ohm thermocouples was RE: [HP-Agilent-Keysight-equipment] Issue with homemade diode power sensor for HP meters
开云体育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:
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On Behalf Of Jeff Kruth via
Groups.Io ? 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:
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[mailto: [email protected]
] On Behalf Of RFI-EMI-GUY ? 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. ? No virus found in this message. No virus found in this message. |
Paul Bicknell