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I need to know the History of FLUKE 87 ( 1988 - 2010 )
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Topic: I need to know the History of FLUKE 87 ( 1988 - 2010 ) (Read 99914 times)
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bluey
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Re: I need to know the History of FLUKE 87 ( 1988 - 2010 )
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Reply #75 on:
June 06, 2020, 10:48:19 am »
Reading the theory of operation more carefully, the resistance function is a comparison function and doesn’t use a “constant current circuit” per se. Therefore the “sanity check” internal resistor test doesn’t achieve that much apart from being a fuse test. The voltmeter could be completely wrong and resistance of the internal resistor would still measure perfectly correct.
Fortunately, the band gap voltage reference in the 87-I to 87-III is quite stable. The LM285BXZ-1.2 Micropower Voltage Reference Diode is described on page 7-58 of the National Semiconductor Linear Databook Vol 2 1988. Long term stability is 20ppm per 1000 hours. Temperature stability is 30ppm/degC.
LMx85-1.2-1988NationalLinearDatabookVolume2.731107566.pdf
(269.77 kB - downloaded 225 times.)
https://usermanual.wiki/Document/1988NationalLinearDatabookVolume2.731107566.pdf
My 1991 87-I never adjusted reads the same as my new Hioki DT4222 - at least for volts.
https://www.eevblog.com/forum/testgear/hioki-dt4222-compact-trms-multimeter-teardown/msg3089246/#msg3089246
86-V and presumably 87–IV (cant find a document listing the parts) use a higher spec 2.5V voltage reference.
https://www.eevblog.com/forum/beginners/what-is-the-voltage-reference-part-in-the-fluke-87-v/msg3089331/#msg3089331
LT1790ACS6-2.5 Micropower SOT-23 Low Dropout Reference Family has tolerance of 0.05% and thermal stability of 10ppm/degC. The voltage reference in 87-I to 87-III has tolerance of 1% and needs trimming to be accurate.
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Last Edit: June 07, 2020, 04:49:01 am by bluey
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