Chapter 4
Theory of Operation
©
National Instruments Corporation
4-3
SCXI-1502 User Manual
The major components of the SCXI-1502 modules are as follows:
•
Rear signal connector
•
SCXIbus connector
•
SCXIbus interface
•
Digital control circuitry
•
Analog circuitry
The SCXI-1502 modules consist of 32 multiplexed input channels, each
with a software-programmable gain of 1 or 100. Each input channel has its
own lowpass filter. The SCXI-1502 modules also have a digital section for
automatic control of channel scanning, temperature sensor selection, gain
selection, and auto-zero mode.
Rear Signal Connector, SCXIbus Connector, and
SCXIbus Interface
The SCXIbus controls the SCXI-1502 module. The SCXIbus interface
connects the rear signal connector to the SCXIbus, allowing a DAQ device
to control the SCXI-1502 module and the rest of the chassis.
Digital Control Circuitry
The digital control circuitry consists of the Address Handler and registers
that are necessary for identifying the module, reading/setting calibration
information, setting the gain, and selecting the appropriate channel.
Analog Circuitry
The analog circuitry per channel consists of a lowpass filter and an
amplifier with a software selectable gain of 1 or 100. The CJ SENSOR
channel has a lowpass filter buffered by a unity gain amplifier. The
channels and CJ SENSOR are multiplexed to a single output buffer.
Analog Input Channels
Each of the 32 differential analog input channels feeds to a separate
instrumentation amplifier with a programmable gain of 1 or 100. Then the
signal passes through a fixed 2-pole, 5 Hz lowpass filter.