Analog Input Circuitry - DAQ DAQCard-1200 User Manual

Chapter 4 Theory of Operation
ACH0
ACH1
ACH2
ACH3
Mux
ACH4
ACH5
ACH6
ACH7
AISENSE/
AIGND
EXTTRIG
EXTCONV*
OUTB1

Analog Input Circuitry

DAQCard-1200 User Manual
Programmable
Gain Amp
GAIN0
GAIN1
GAIN2
6
Dither
Dither Circuitry
External Trigger
External Convert
Output B1
The analog input circuitry consists of two analog input multiplexers, mux
counter/gain select circuitry, a software-programmable gain amplifier, a
12-bit ADC, and a 12-bit FIFO memory that is sign-extended to 16 bits.
The two input multiplexers route the input channels to the instrumentation
amplifier in either RSE, NRSE, or DIFF input mode. The input
multiplexers provide input overvoltage protection of ±35 V powered on and
±25 V powered off.
The mux counters control the input multiplexers. The DAQCard-1200
can perform either single-channel data acquisition or multiple-channel
(scanned) data acquisition. These two modes are software-selectable.
For single-channel data acquisition, you select the channel and gain before
initiating data acquisition. These gain and multiplexer settings remain
constant during the entire DAQ process. For multiple-channel data
acquisition, you select the highest numbered channel and gain before data
acquisition is initiated. Then the mux counter decrements from the highest
numbered channel to channel 0 and repeats the process. Thus you can scan
any number of channels from eight to two. Notice that the same gain setting
is used for all channels in the scan sequence.
A/D
Data
Sample-
12-Bit
and-Hold
ADC
12
Amp
Gain
Select/Mux
Counter
Dither Enable
DAQ
Counter/Timer
Timing
Signals
Figure 4-4. Analog Input Circuitry
4-6
Data
12
1 K
Sample
A/D
FIFO
Data
CONV
AVAIL
Data
8
8
WRT/RD
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