Wishcolor LM399 5 ½ or 6 ½ Digit High Precision Voltage Reference for Multimeter Calibration
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ordered first at 2025-06-13 11:42:45 delivery at 2025-06-30 13:13:00 apparently a good calibrator for 5.5 digit multimeters on 10v output may be used to see 6.5 digit multimeters drift, but drifts itsels a bit I have two and the first had nominal 10v voltage of 9.93294 I write feedback on the second unit after I have burnt it up, and got longer term expereience on it. first unit: kept it powered for 15 days (360 hours) measured at 29c temperature (29-23=6c): min/max nom 10v voltage measured with a Rigol 3068 still in valid calibration using math/ trend mode : 6h40 nom 9.93294 min 9.933025- max 9.933074 error (variation) 134-269uV (13-27 ppm) min/max nom 6.95v voltage measured with a Rigol 3068 still in valid calibration using math/ trend mode : short time error (variation) 6,99804 nom 6,99806V measured variation 20uV (+2.85ppm) , inside the specs (3,5uV/c +6c 0.5ppm/c = 3ppm) 9,93294 nom 9,93304 measured variation 10uV (+10ppm) a bit outside specs (9,99uV/c +6c 1ppm/c= 6ppm) 1h40 trend of 6.95v output: nom 6,99804 min 6.998065 - 6.998095 25-55uV 3.57-7.86ppm (specs 0.5ppm/c x 6c = 3 ppm) not quite on specs but noise is not in specs. in summary a good piece of kit for it's price ( I paid about 30€ including shipping) in summary a good for it's price