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cr1901_modern>
I hope compiling LLVM goes right on Windows this time... last time, it complained that std::tie didn't exist
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GitHub142>
artiq/master cd3b590 Sebastien Bourdeauducq: language/scan: add missing attributes to RandomScan...
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travis-ci>
m-labs/artiq#497 (master - cd3b590 : Sebastien Bourdeauducq): The build is still failing.
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sb0>
whitequark, do you have an idea of the typical voltage across a pirani gauge?
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whitequark>
sb0: what's the resistance?
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whitequark>
this gauge I have consumes 0.5W at atmospheric. at most half of that will end up in the filanemt
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sb0>
about 100 ohm
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sb0>
I have only the filament
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sb0>
no control circuit
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whitequark>
well, that would be 25mV at most
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whitequark>
assuming the filaments are alike
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whitequark>
why don't you make a bridge and then pump it down while using a lab power supply and a scope?
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sb0>
a bridge with what resistor values?
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sb0>
right now I'm putting a few volts into it, and see a variation of some milliamperes that depends on the vacuum
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whitequark>
the resistor values in a bridge are ideally all identical
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sb0>
ah, right. but then what voltage do I put across the bridge?
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whitequark>
in practice, I would take the gauge, two 100 ohm 0.1% resistors, and one 100 ohm potentiometer to balance it out
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whitequark>
the voltage doesn't particularly matter
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whitequark>
because what you are measuring is the change in resistance relative to the applied voltage
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sb0>
and then I have to build an instrumentation amplifier and all that bling?
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whitequark>
use a differential opamp. the output will grow proportionally to supply voltage
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sb0>
yeah, but doesn't the gauge have an optimal temperature?
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sb0>
instrumentation amplifier == differential opamp + stable and reasonable gain
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whitequark>
(optimal temp) not really
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whitequark>
what you want is it to be reasonably warmer than your system
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sb0>
and that requires 3 regular opamps
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whitequark>
but not warm enough to reduce filament life
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whitequark>
usually they aim at 80°C
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