*'如果你真的对低漂移感兴趣，请保持你的仪表24/7/365'*对不起，该声明不一定正确！
首先，环境条件为8 / 4ppm /年。
没有指定3458A的漂移！
不是说，这种漂移是否只能在24/7/365模式下实现，或者是否也允许将其关闭。
仅在维修说明18B中，有一个提示，即如果长时间无电，电压参考可能会显示迟滞或可能会忘记其调节。
3458A内部的LTZ1000A运行温度约为90-95°C。
凌力尔特公司计划在65°C下运行，每年约1-2ppm。
通常漂移。
温度高30°C有两个影响：首先，每10°C老化约两倍。
（参考：Spreadbury，Pickering）这导致漂移率比预期高8倍（=> 8 - 16ppm /年！）。
Spreadbury还表示，无动力的LTZ1000引用几乎不会漂移。
因此，LTZ1000A的较低温度会通过降低炉温来改善漂移率。
大部分时间断电肯定会减少年度漂移。
其次，如果LTZ1000在高于室温约> 40°C的温度下运行，则会显示出滞后效应。
另请参阅皮克林专利，以通过热循环消除滞后现象。
在这种情况下，LTZ1000A在95°C下运行并在@ HP / Keysight工厂的该温度下预先调节，将显示蠕变效应。
滞后将缓慢，例如。
几个月后，恢复到LTZ的室温值。
一些参考文献会很快完成，其他参考文章会更慢。
这就是SN 18B的背景！
再次上电后，LTZ可能需要更多时间来稳定到原始值。
如SN18B所述，这可能只是几个小时，也可能是6周。
显然，当时安捷伦有一批非常敏感的参考文献。
但是滞后/恢复效应通常应该在亚ppm级别。
我测量了几个LTZ的预热时间，并且在3-6分钟内全部恢复到0.2ppm的初始值。
我自己的3458A（65°C烤箱）显然既没有滞后效应，也没有过度漂移（它的漂移几乎为零），虽然我总是在测量后将其断电，以节省能源，并避免不必要地消耗其MTBF。
坦率
以上来自于谷歌翻译
以下为原文
*'if you are really interested in low drift, keep your meter on 24/7/365'*
Sorry, that statement is not necessarily correct!
First, the environmental conditions for the 8/4ppm/yr. drift of the 3458A is not specified at all!
It's not said, whether this drift will be achieved in 24/7/365 mode only, or if it's also allowed to switch it off.
Only in Service Note 18B, there is a hint, that the voltage reference might show hysteresis or might forget its conditioning, if left unpowered for an extended period of time.
The LTZ1000A inside the 3458A is running on about 90-95°C.
Linear Technology intended it to be run on 65°C, giving about 1-2ppm/yr. drift typically.
This 30°C higher temperature has two effects:
First, the ageing is about doubled every 10°C. (Ref.: Spreadbury, Pickering)
This leads to 8 times higher drift rates (=>8 - 16ppm/yr.!) than intended.
Spreadbury also showed, that unpowered LTZ1000 references do not drift at all, nearly.
Therefore, a lower temperature of the LTZ1000A would improve the drift rate, by reducing the oven temperature.
Powering down for most of the time will definitely decrease the annual drift.
Second, the LTZ1000 shows a hysteretic effect, if it is operated at about > 40°C above room temperature.
See also Pickering patent for removing that hysteresis by thermal cycling.
In this case, an LTZ1000A, which runs on 95°C and has been pre-conditioned at that temperature @ HP / Keysight factory, will show a creeping effect.
The hysteresis will slowly,e.g. over months, recover towards the room temperature value of the LTZ.
Some references will do that quickly, other more slowly. That's the background of SN 18B!
After powering up again, the LTZ might need more time to stabilize to the original value.
That can be either a few hours only, or 6 weeks, as described in the SN18B.
Obviously, agilent had a very sensitive batch of references at that time.
But that hysteresis / recovery effect should normally be on sub ppm level.
I have measured the warm-up time of several LTZs, and all returned to their initial value within 0.2ppm in 3-6 minutes.
My own 3458A (65°C oven) obviously shows neither hysteretic effects, nor excessive drift, (its drift is nearly zero), although I always power it down after measurements, to save energy, and also to avoid consuming unnecessarily its MTBF.
Frank
*'如果你真的对低漂移感兴趣，请保持你的仪表24/7/365'*对不起，该声明不一定正确！
首先，环境条件为8 / 4ppm /年。
没有指定3458A的漂移！
不是说，这种漂移是否只能在24/7/365模式下实现，或者是否也允许将其关闭。
仅在维修说明18B中，有一个提示，即如果长时间无电，电压参考可能会显示迟滞或可能会忘记其调节。
3458A内部的LTZ1000A运行温度约为90-95°C。
凌力尔特公司计划在65°C下运行，每年约1-2ppm。
通常漂移。
温度高30°C有两个影响：首先，每10°C老化约两倍。
（参考：Spreadbury，Pickering）这导致漂移率比预期高8倍（=> 8 - 16ppm /年！）。
Spreadbury还表示，无动力的LTZ1000引用几乎不会漂移。
因此，LTZ1000A的较低温度会通过降低炉温来改善漂移率。
大部分时间断电肯定会减少年度漂移。
其次，如果LTZ1000在高于室温约> 40°C的温度下运行，则会显示出滞后效应。
另请参阅皮克林专利，以通过热循环消除滞后现象。
在这种情况下，LTZ1000A在95°C下运行并在@ HP / Keysight工厂的该温度下预先调节，将显示蠕变效应。
滞后将缓慢，例如。
几个月后，恢复到LTZ的室温值。
一些参考文献会很快完成，其他参考文章会更慢。
这就是SN 18B的背景！
再次上电后，LTZ可能需要更多时间来稳定到原始值。
如SN18B所述，这可能只是几个小时，也可能是6周。
显然，当时安捷伦有一批非常敏感的参考文献。
但是滞后/恢复效应通常应该在亚ppm级别。
我测量了几个LTZ的预热时间，并且在3-6分钟内全部恢复到0.2ppm的初始值。
我自己的3458A（65°C烤箱）显然既没有滞后效应，也没有过度漂移（它的漂移几乎为零），虽然我总是在测量后将其断电，以节省能源，并避免不必要地消耗其MTBF。
坦率
以上来自于谷歌翻译
以下为原文
*'if you are really interested in low drift, keep your meter on 24/7/365'*
Sorry, that statement is not necessarily correct!
First, the environmental conditions for the 8/4ppm/yr. drift of the 3458A is not specified at all!
It's not said, whether this drift will be achieved in 24/7/365 mode only, or if it's also allowed to switch it off.
Only in Service Note 18B, there is a hint, that the voltage reference might show hysteresis or might forget its conditioning, if left unpowered for an extended period of time.
The LTZ1000A inside the 3458A is running on about 90-95°C.
Linear Technology intended it to be run on 65°C, giving about 1-2ppm/yr. drift typically.
This 30°C higher temperature has two effects:
First, the ageing is about doubled every 10°C. (Ref.: Spreadbury, Pickering)
This leads to 8 times higher drift rates (=>8 - 16ppm/yr.!) than intended.
Spreadbury also showed, that unpowered LTZ1000 references do not drift at all, nearly.
Therefore, a lower temperature of the LTZ1000A would improve the drift rate, by reducing the oven temperature.
Powering down for most of the time will definitely decrease the annual drift.
Second, the LTZ1000 shows a hysteretic effect, if it is operated at about > 40°C above room temperature.
See also Pickering patent for removing that hysteresis by thermal cycling.
In this case, an LTZ1000A, which runs on 95°C and has been pre-conditioned at that temperature @ HP / Keysight factory, will show a creeping effect.
The hysteresis will slowly,e.g. over months, recover towards the room temperature value of the LTZ.
Some references will do that quickly, other more slowly. That's the background of SN 18B!
After powering up again, the LTZ might need more time to stabilize to the original value.
That can be either a few hours only, or 6 weeks, as described in the SN18B.
Obviously, agilent had a very sensitive batch of references at that time.
But that hysteresis / recovery effect should normally be on sub ppm level.
I have measured the warm-up time of several LTZs, and all returned to their initial value within 0.2ppm in 3-6 minutes.
My own 3458A (65°C oven) obviously shows neither hysteretic effects, nor excessive drift, (its drift is nearly zero), although I always power it down after measurements, to save energy, and also to avoid consuming unnecessarily its MTBF.
Frank
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