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Operation Theorem
4.1 A/D
Conversion
When using an A/D converter, you should know about the properties of
the signal to be measured at first. Users can decide which channels to
use and connect the signals to USBDAQ-9100MS. Please refer to 3.2. In
addition, users should define and control the A/D signal source, including
A/D channels, A/D gains, and A/D signal types.
Sampling Process:
USBDAQ-9100MS supports Post-Trigger Mode which means the
acquisition starts after the trigger condition happen. The trigger source
can be External Input(TGIN), Counter Output and Software command
(Default).
After the trigger condition occurred, the A/D acquisition starts
automatically. USBDAQ-9100 uses four A/D converters and the input
channels are divided into two banks. Bank one is channel 1, 3, 5, 7 and
Bank two is channel 2, 4, 6, 8. The data acquired in the channels of the
same Bank are simultaneously and after the first bank of data is
converted, it will start to scan the other bank of data. Any one of the
channels in the Bank can be enabled or disabled and if all the channels in
the Bank are disabled, they will not be scanned in the data acquisition.
The scan frequency is defined in the Scan Interval Counter (
SIC
). The
SIC is a 24-bit register and the scan frequency is calculated as:
Scan Frequency=TimeBase Frequency (32MHz) / SIC
That is Scan Interval (ScanConv) = SIC / TimeBase
In the software driver, the Scan Frequency is equal to the variable,
ScanRate
The sampling interval (ScicConv) is measured by the period from Bank
One scan to Bank Two scan. The software driver fixed the sample
interval to be half of the Scan Interval, that is
SCIC counter = 0.5 * SIC
Thus
Sampling interval (ScicConv) = SCIC / TimeBase = 0.5 * SIC / TimeBase
Since the software had fixed the Sampling interval to be half of Scan
Interval, therefore once
ScanRate
is fixed, Sampling rate is decided.
The total number of scan is specified by the register, SC which is equal to
the variable,
ReadCount
in the software driver.
Summary of Contents for USBDAQ-9100MS
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