2.4 BIPOLAR/UNIPOLAR AND GAIN SETTING
The Bipolar or Unipolar configuration of the A/D converter is set by switch S2 (Figure 2-3). The switch
controls all A/D channels. Though you cannot run some channels bipolar and some unipolar, you can
measure a unipolar input in the bipolar mode. (e.g. you can monitor a 0 to 5V input with a +/-5 V
channel)
Figure 2-3. Bipolar/Unipolar Select Switch
The input amplifier gain is selectable by software.
2.5 CONVERSION START, EDGE SELECT
The original Keithley MetraByte DAS-1600 was designed such that A/D conversion was initiated on the
falling edge of the convert signal. Neither the original DAS-16, nor any of the other DAS-16 derivative
converts on the falling edge. In fact, we are not aware of any A/D board that uses the falling edge to
initiate the A/D conversion.
When using the falling edge to start the conversion, the A/D may be
falsely triggered by 8254 pacer clock initialization glitching (easy to
avoid but a real possibility in the DAS-1600). Converting on the falling
edge mode also may lead to timing differences if the
PCIM-DAS1602/16 board is being used as a replacement for an older
DAS16 series board. Because using the falling edge trigger was
undesirable, we have designed a jumper into the PCIM-DAS1602/16
which allows you choose the edge that starts the A/D conversion. The
PCIM-DAS1602/16 is shipped with this jumper in the rising edge
position.
Figure 2-4 to the right shows the edge selection options.
For compatibility with all third party packages, with all DAS-16
software and with PCIM-DAS1602/16 software, leave this jumper in
the rising edge position.
Figure 2-4. Trigger Edge-Select
Jumper
2.6 D/A CONVERTER REFERENCE & SSH JUMPER BLOCK
The jumper block located near the center of the PCIM-DAS1602/16 allows you to use the on board
precision voltage reference to select the output ranges of the digital to analog converters.
3
TRIGGER EDGE SELECT
JUMPER BLOCK
P8
P8
Falling Edge A/D Trigger
DAS-1600 Method
Rising Edge A/D Trigger
DAS-16 Method
Default
Setting
Содержание PCIM-DAS1602/16
Страница 4: ...This page is blank ...
Страница 48: ...For your notes 44 ...