Detailed Circuit Description; Dc Scaling - Fluke 8842A Instruction Manual

8842A
Instruction Manual

5-3. DETAILED CIRCUIT DESCRIPTION

The following paragraphs give a detailed circuit description of each of the functional
blocks in Figure 5-1. For clarity, measurement ranges are referred to as r1, r2, r3, etc.,
where r1 is the lowest possible range, r2 the next higher range, and so on. Pins are
designated by the respective integrated circuit (e.g., U101-7 for U101 pin 7).

5-4. DC SCALING

The DC Scaling circuit scales all in-range dc inputs so that the output of the Track/Hold
(T/H) amplifier (U307) is within +/-2V. In addition, the DC Scaling circuit provides input
protection and analog filtering. Additional scaling is provided by the the T/H Amplifier.
The following paragraphs describe the configuration of the DC Scaling circuit in the
DCV and mA DC functions and also describe the analog filter. The ohms functions are
described under a later heading because the T/H Amplifier provides additional input
switching for these functions.
5-4