Testing Ohms Input - Fluke 525A Service Manual

525A
Service Manual

Testing Ohms Input

Before measuring ohms input, the ohms output of a 5520A must be "characterized". To
achieve the needed accuracy, the Wavetek 1281 is used as a transfer standard and the
742A is used as the reference standard. To find the true value of the 5520A output, the
ratio-input function of the Wavetek 1281 is used. The ratio function of the 1281 is located
on the rear panel and is designated as Channel A and Channel B. Connect Channel A to
the 742A and connect the 5520A to Channel B, both using four-wire measure.
See Figure 12 for a connection diagram.
For the 400 Ω range use the 742A-1K and for the 4 kΩ range use the 742A-10K. For
more information on the correct usage of ratio mode refer to the 1281 Operators Manual.
Use Table 15 to note the ratio indication on the 1281. Ignore the 0 Ω value. Use the
formula (742A actual value/ratio indication * 100 = actual 5520A value) and enter that
ohm value into the 5520A actual value column.
30
1281
Chan A
31 28 23 21
Pin
+
-
Hi I I Lo
742
Figure 12. 1281 Connection Diagram
Rear inputs Chan B
31 28 23 21
+
-
Hi I I Lo
Pin
5520A
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