Chapter 4
Theory of Operation
DAQCard-1200 User Manual
4-6
ni.com
Figure 4-4.
Analog Input Circuitry
Analog Input Circuitry
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.
Dither
Circuitry
Dither Enable
Dither
I/O
Connector
ACH0
ACH1
ACH2
ACH3
ACH4
ACH5
ACH6
ACH7
AISENSE/
AIGND
Mux
EXTTRIG
EXTCONV*
OUTB1
Programmable
Gain Amp
Sample-
and-Hold
Amp
12-Bit
ADC
A/D
Data
12
1 K
Sample
A/D
FIFO
Data
12
CONV
AVAIL
Decode
Circuitr
y
GAIN0
GAIN1
GAIN2
Gain
Select/Mux
Counter
Data
8
WRT/RD
Con
v
e
rt
6
External Trigger
External Convert
Output B1
DAQ
Timing
Counter/Timer
Signals
PCMCIA
Interf
ace
PCMCIA
I/O
Channel
8
Data