XITRON 2000I, Руководство пользователя

Страница: 58 / 96

58
2000I & 2000M User Guide, Rev B
3.
Select the “Standby” state.
4.
Select the Measure mode of operation.
Engineering Laboratory Environment Applications
The 2000 instruments have many uses in the Calibration and Engineering
Laboratory environments.
Short-Term Transfer Standards
The 2000 instruments can be used for medium accuracy transfers in the
calibration laboratory based on their:
•
DC voltage 24-hour stability (at the 10V level) of 2 . 1ppm, and
•
DC current 24 hour stability (at the 1mA level) of 6 . 0ppm,
The excellent low level stability of these instruments also enable them to be
used as a bucking type of source for inter-cell comparisons with 0.2ì V
uncertainty below 22mV. Refer to Table 1.
The short-term stability for current output enables the use of the 2000
instruments for resistance transfers. In this application the 2000I or 2000M
instrument is set to a suitable current for the resistance to transfer—a 10V
drop across the resistor. A high accuracy digital voltmeter is used to measure
the voltage drop across the standard. On the same the standard resistor is then
replaced by a resistor of unknown value (one within a 10:1 ratio of the
standard).
The value of the unknown resistance is then given by the formula:
R
unknown
= R
standard
* (V
unknown
/ V
standard
)
Note that this method yields better performance, at higher values, than the
normally used practice of placing the two resistors in series and measuring
the voltage across each resistor. This is because the voltmeter usually has
leakage current flow to ground in one terminal (usually the LO terminal),
which unbalances the circuit for the two measurements. In this method, the
circuit is in the same conditions for each measurement, thus this effect is
eliminated. The major item affecting accuracy is the finite output impedance
of the current source, which is only of importance when the two resistor
values are significantly different.