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Section 3
Principles of Operation
3.1
Introduction
The Model 2835-C’s electronics adapt to a number of signal measurement
tasks: DC current or voltage, AC peak-to-peak current or pulse voltage, or
integrated DC current or voltage signals. This versatility is required to handle
the various signals that Newport’s
Low-Power, High-Power
and
Energy
detector families generate. These detector families are based on semiconduc-
tor, thermopile and pyroelectric detectors respectively. Detector data is
introduced to the Model 2835-C by way of a calibration module specific to the
detector in use. At power up (and RESET), the 2835-C uploads information
about the detector from the calibration module which describes the set of
operating states available to the detector. A user then selects among the
available operating states when using the meter. Front panel control and the
operating states of the Model 2835-C are discussed in Sections 2.3 and 2.4.
3.2
Analog Signal Flow
Detector signals can follow many different paths through the Model 2835-C
input amplifier chain. A block diagram of analog signal flow is shown in Figure
9. The actual flow path depends upon the detector type and the mode of
measurement.
Prog. Transimpedence
Current Amp.
Prog. Voltage
Amp.
Prog. Bandwidth
Noise Filter
Voltage
Buffers
Analog
Output
Peak
Detector
Baseline
Hold Circuit
4,096 Cnt
20,000 Cnt
Peak - Peak &
Peak - Baseline
A/D
A/D
+
–
I
V
Input
Figure 9 – Model 2835-C Analog Signal Flow Diagram
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