Author Topic: I need to know the History of FLUKE 87 ( 1988 - 2010 )  (Read 78038 times)

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Offline bluey

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Re: I need to know the History of FLUKE 87 ( 1988 - 2010 )
« 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.

[attach=1]
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.
« Last Edit: June 07, 2020, 04:49:01 am by bluey »
 
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