Chapter 3; Theory Of Operation; Functional Systems; Input Channels 1 & 2 System - Racal Instruments 2461 User Manual

2461Type C User Manual
Functional
Systems
Input Channels 1
& 2 System
Racal Instruments  1998
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THEORY OF OPERATION

The 2461 Type C card comprises 3 functional systems as
follows:
1. The Input Channels 1 & 2 System
2. The Input Channel 3 System
3. The Measurement System
4. The Microprocessor System
The Input Channels 1 and 2 System comprises two channels that
process the signals applied to Input 1 and Input2 respectively to
produce differential pairs of signals that are fed to the
measurement system. A block diagram is given in Figure 3-1.
Each channel includes relay-controlled circuits which allow
selection of 50Ω/1MΩ input impedance, AC/DC coupling, X1/X10
input attenuation and 50kHz filter. A further relay allows the user
to choose between SEPARATE and COMMON modes of
operation. In SEPARATE mode the signal on Input 1 is fed to the
channel 1 active circuits and the signal on Input 2 is fed to the
channel 2 active circuits. In COMMON mode the signal on Input
1 is fed in parallel to both the channel 1 and channel 2 active
circuits. In this mode signals on Input 2 are disconnected from
the channel 2 active circuits, but remain connected to the
50Ω/1MΩ, AC/DC and X1/X10 selection circuits.
Each channel features separate high frequency and low
frequency paths whose outputs in normal operation are
recombined with a crossover frequency of 5kHz nom. With
FILTER selected, the high frequency path is disabled, and the
bandwidth of the low frequency path set to 50kHz nom. The
buffered signals from each channel drive separate ground-
referenced Schmitt trigger output stages.

Chapter 3

Theory Of Operation 3-1