LM299AH-20 Ovenized Voltage Reference
A case study of 78 peices from Date Code H9448
UNDER CONSTRUCTION June, 2013
We recently had an opportunity to purchase 10 boxes of new old stock LM299AH-20 ovenized voltage references manufactured by National Semiconductor about 1994 (one box had only 8 parts). The outer cardboard boxes had been opened. Each reference is in an anti-static bag. About half of them had apparently been opened and then restapled. It might have been an end user opening each one to look at the data sheet contained within. None of the references show any sign of bent leads, scratch marks, or soldering.
Each reference carries its own unique serial number applied by National Semiconductor with a matching printed data sheet.
If someone has a distributor catalog from about 1994, much appreciated if we could obtain a PDF from a catalog or brochure, particlarly if it shows the price for a LM299AH-20 on or about 1994.
From the '94 data sheet (see page 4) PDF:
"Certified Long Term Drift The National Semiconductor LM199AH-20, LM299AH-20, and LM399AH-50 are ultra-stable Zener references specially selected from the production runs of LM199AH, LM299AH, LM399AH and tested to confirm a long-term stability of 20, 20, or 50 ppm per 1000 hours, respectively. The devices are measured every 168 hours and the voltage of each device is logged and compared in such a way as to show the deviation from its initial value. Each measurement is taken with a probable-worst-case deviation of +/-2 ppm, compared to the Reference Voltage, which is derived from several groups of NBS-traceable references such as LM199AH-20's, 1N827's, and saturated standard cells, so that the deviation of any one group will not cause false indications. Indeed, this comparison process has recently been automated using a specially prepared computer program which is custom-designed to reject noisy data (and require a repeat reading) and to record the average of the best 5 of 7 readings, just as a sagacious standards engineer will reject unbelievable readings. The typical characteristic for the LM199AH-20 is shown below. This computerized print-out form of each reference's stability is shipped with the unit."
A preliminarly chart shows the raw reported drift with time for these 78 new old stock parts PDF. It appears highly unlikely that 78 parts would make wide swings all together. On the other hand, 78 parts make a nice average to possibly remove the error. We re-plotted the data correcting for the average of the group drift. The corrected plot appears more plausible PDF. It is very likely that the reference voltmeter drifted over the 1008 hour test period for this group of 78 parts. There are still some odd swings in the "corrected" data, which might indicate different reference meters and/or different test sets and/or an entirely different 1008 hour test period (thus different reference meter drift).
Excel Worksheet with raw data XLS.
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COPYRIGHT © 2013 JOSEPH M. GELLER