Fluke 5700A Series II - Cables; Guarding; Sensing

5700A/5720A Series II
Operators Manual
4-52
4-55. Cables
According to the text under “Connecting the Calibrator to a UUT,” the 5440A-7002
(banana plugs) or 5440A-7003 (spade lugs) Low-Thermal Cables are recommended for:
•
All DC voltage
•
All resistance
•
AC voltage <10 kHz
•
AC current ≤2 A ≤ 0 kHz
•
DC current ≤ 2A
Since all of the 70 Series tests include these functions, you should use the 5440A-7002 or
5440A-7003 Low-Thermal Cables, if possible. However, the thermal emf errors that the
Low-Thermal cables are designed to reduce are not significant when calibrating a 3½
digit meter. Therefore, if you have the recommended Low-Thermal Cables, use them.
Otherwise, ordinary insulated test leads will suffice.
4-56. Guarding
Because the 70 Series Multimeters are battery operated, their inputs have no connection
to earth ground. Therefore, setting the calibrator to internal guard is appropriate.
4-57. Sensing
External sensing is required only when the voltage drop in the cables is significant. The
following data determines the significance of the voltage drop in the cables:
•
The input impedance of the 70 Series Multimeters is 10 MΩ.
•
The total resistance of the Model 5440A-7002 Low-Thermal Cables is 30 mΩ.
•
The basic dc voltage accuracy of the most accurate of the 70 Series, the Model 77, is
0.3%.
The percentage of error caused by voltage drop in the cables is:
0.3 x 100/10,000 = 0.003%, or 1/100th of the accuracy of the Model 77.
This voltage drop is not significant, so a two-wire connection (Internal Sense) is
appropriate.