[volt-nuts] 3458a RAM batteries - longer life if unit is continually powered?

[Tom Miller]

Only on the newer (AB & AD) Dallas (Maxim) parts. All the old ones (Y) do 
not have that feature.

Tom M.

----- Original Message ----- 
From: "Tom Knox" <actast at hotmail.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Thursday, March 27, 2014 12:59 PM
Subject: Re: [volt-nuts] 3458a RAM batteries - longer life if unit is 
continually powered?


Date Codes can be misleading because most of this style of chip does not 
connect to the battery until the first power up cycle. So evl

Thomas Knox



> Date: Thu, 27 Mar 2014 17:33:17 +0100
> From: frank.stellmach at freenet.de
> To: volt-nuts at febo.com
> Subject: [volt-nuts] 3458a RAM batteries - longer life if unit is 
> continually powered?
>
> Hi,
>
> the DALLAS datasheet specifies 10 years data retention. Quite obviously,
> that's the unpowered time.
>
> That time includes self discharge and RAM sustaining currents.
>
> self discharge and RAM supply current will be of the same order, i.e. <
> 1µA, I assume from experience.
> And I assume also, that those currents will vary over samples, i.e. over
> samples of battery and RAM.
>
> Recently, there was the case, where the CAL RAM was still alive after 24
> years (instrument vintage 1989, same DALLAS date code!), but with
> unknown powering history.
>
> Additionally, a typical 10 years of lifetime is given also for those
> batteries.
>
> Therefore, in practise there will be no pronounced difference between
> powered / unpowered state.
> On the other hand, DALLAS implemented an electronic seal, so that the
> RAM inside the package is initially powered only after first power up.
> But there's no parameter in the datasheet, specifying data retention
> according to date code or to initial power up.
>
>
> The waste of energy just to extend the batteries lifetime, does not pay 
> off.
> On the contrary, the MTBF time of the instrument will be consumed, the
> display will get bad, and here in Germany, this energy consumption would
> cost a fortune (meanwhile: 25+ Cents / kWh, crazy).
>
>
> Yes, as long the instrument is powered, the CAL RAM will not lose its
> content.. but what about unexpected power outages?
>
>
> If you save the CAL RAM and repogram a fresh one after failure, there's
> no need to send it to agilent.
>
>
> No, not any RAM error needs recalibration.
> Those error messages are not documented.
>
> So I've scanned the text fragments in the firmware file:
>
> RAM TEST 1
> RAM TEST 2
>
> probably refer to either to the configuration RAMs (2x32kB), andthe CAL
> RAM (8kB).
>
> Eror messages are:
> NONVOLATILE RAM HiGH /LOW
> CAL RAM FAILURE
>
> and known ones from other users:
>
> RAM TEST 1 HIGH / LOW
>
> So I assume, that a real failure of the cal constants only apply on
> message: CAL RAM FAILURE and perhaps RAM TEST 2 ...., as RAM TEST 1
> should refer to the configuration RAMs only, HIGH to the high byte RAM,
> LOW to the low byte RAM.
>
> Errors of the cal RAM will manifest in additional ACAL or CAL failures.
>
>
> Frank
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