[volt-nuts] Fluke 7000 , 7001 system

[Frank Stellmach]

Hi,

there are plenty of arguments for terminating this system:

1.Fluke has bought this Datron design obvioulsy to eliminate a 
competitor, So it's normal, that sooner or later, one of both products 
would vanish.
2. It's too expensive to maintain two concurrent systems. Therefore one 
had to die, and it's natural, that the original Fluke system would survive.
3. The 7001 contains the LTZ1000, (non A-version, and only one), which 
is non-proprietary like the LTFLU ref amp. in the 732B.
4. The 7001 did perhaps not prove its advantage over the 732B, either in 
term of stability, or in terms of hysteresis reduction.

We've discussed that on eevblog also, the volatile part of all those 
references is the 7.2V => 10V transfer, depending on precision resistors.
The 732B uses specially selected resistors, and the 7001 has this 
statistical resistor array. Both have stability figures over 1ppm/yr., 
and to my estimations/calculatiuon, this is mainly due to the 
instability of the amplifier resistors.
The ref. amplifiers themselves, using  buried zener diodes, have an easy 
potential instability of < 0.3ppm/yr.
Therefore, the 7001 did not have an advantage over the 732B in this aspect.

The promised removing of hysteresis by teperature cycling, as described 
in the Pickering patent, will not work correctly in the 7001. The reason 
is, that additionally a stabilization temperature of 45°C has been 
chosen, to have a smaller drift rate than at 65°C. (see Spreadbury article)

In the Pickering patent a center temperature of at least 65°C has been 
sketched, and a symmetrical tempe. cycling pattern is required.
This will not work on 45°C, where +/-20°C is possible only, and this is 
not sufficient to remove effects from a trip to temperatures below 20°C, 
or even 0°C, as promoted.
Also, in an interval of +/-20°C around the 45°C stabilization 
temperature, there is practically not hysteresis effect visible. (This I 
could see on the cycling of my both LTZ100 references.)

Therefore, the hysteresis removing technique was not successful to my 
opinion in the 7001, making it unnecessarily expensive.

Frank