IET Labs PRS-370 SERIES, Operation Manual

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PRS-DMM MODE
PRS-370 Series
23
Chapter 4
PRS-DMM Mode
4.1 PRS-DMM Mode
4.1.1 Overview
When PRS-DMM mode is turned on this allows
the PRS-370 to control, via the IEEE interface,
either a Fluke 8508A DMM or Keysight 3458A
DMM and automatically adjust the output source
resistance based upon measurements from the
DMM.
The DMM is used to measure the resistance of the
PRS-370, and
fi rmware routine in the PRS-370
adjusts the output resistance to achieve the closest
possible resistance value to the target resistance
value.
This can improve the accuracy of the PRS-370
from ±(70 ppm + 1 m
Ω ) to <10 ppm short-term
without switching.
NOTE: If the IEEE card does not see a
controller signal, the PRS-370 assumes control
over the IEEE bus to function in PRS-DMM
Mode.
If the PRS-370 has been controlled via a PC
the IEEE cable must be disconnected from the
PRS-370 and the power cycled on the PRS-370.
This allows the PRS-370 to assume control over
the IEEE bus to function in PRS-DMM Mode.
4.1.2 General Requirements
PRS-DMM Mode allows the PRS-370 to control
a Fluke 8508A or Keysight 3458A DMM via the
IEEE interface.
A GPIB cable must be connected between the
IEEE interface on the PRS-370 and the IEEE
interface on the DMM.
The rear binding post of the PRS-370 should be
connected to the front binding post of the DMM
using a high quality, 4 terminal kelvin connection.
No shorting links should be used on the front or
rear binding posts of the PRS-370.
The PRS-370 con fi gures the DMM for resistance,
triggers the DMM to perform a measurement of
resistance, and reads the resistance back from the
DMM. The source resistance of the PRS-370
is then adjusted to achieve a closer value to the
nominal. This process can be repeated in a loop
up to 5 times.
Once the process is complete the nominal value,
measured value from the DMM, delta from
nominal and the absolute uncertainty at k = 2 of
the DMM is shown on the display. See Figure 4-9
Absolute uncertainty is based upon catalog
speci
fi cations given in the instruction manuals for
the Keysight 3458A or Fluke 8508A based upon
1 year absolute uncertainties for TCAL ± 1
°C.