User`s guide
34 • Operation Theory
4.1.1 A/D Conversion Procedure
To use the A/D converter, users first need to know the properties of the signal
being measured. Users then can decide on which channels to use on the
PCI-9111. Refer to section 2.7 ‘Connectors Pin Assignment’. In addition,
users need to define and control the A/D signal sources, including the A/D
channel, A/D gain, and A/D signal types. Refer to section 4.1.2. For A/D signal
source control.
After deciding on the A/D signal source, users must decide how to trigger the
A/D conversion and define/control the trigger source. The A/D converter will
start to convert analog signals to a digital value when a trigger signal is on a
rising edge. Refer to the section 4.1.3 for all possible trigger modes.
The A/D data should be transferred to the PC's memory for further processing
is required. The data can be read either by an I/O instruction set, which is
handled directly by software or transferred to memory via an interrupt routine.
Refer to section 4.1.4 for more information regarding multi-configurations for
the A/D data transfer process.
Some applications may require obtaining the data only before or after special
hardware event. The Pre-Trigger is useful to stop the A/D operation. Refer to
section 4.1.5 for configuring the PCI-9111 for Pre-Trigger Mode.
To process the A/D data, programmer should have n understanding of the A/D
data format. Refer to section 4.1.6 for details.
4.1.2 A/D Signal Source Control
To control the A/D signal source, the signal type, signal channel and signal
range should be considered.
Signal Type & Signal Conditioning
The A/D signal sources of the PCI-9111 can only be single ended (SE). There
are 16 SE A/D channels on board. A R/C filter (attenuators) is implemented on
each channel. The RC circuit is shown in the diagram below, where ‘n’ is the
channel number. User can install different R, C values for special purposes
such as attenuating the voltage to increase the input voltage range.
Figure 9. RC Circuit on Input channel
RA n
0
Ohm
To Multiplexer
Analog Input
Channel #n
RB n
OPEN
CA n
OPEN