digiBASE
®
PMT Base with Integrated Bias Supply, Preamplifier and Digital Multichannel Analyzer
931003E / 0620
A.2. Throughput Issues
In List Mode, each event received by the detector results in the transmission of a 32-bit data
word to the computer. In extreme situations with multiple digiBASEs connected to a single com-
puter, the data rate can overwhelm the computer. As an example, if a source is placed in front of
the detector that results in 10 kcps accumulating in a histogram, ten thousand 32-bit data words
must be transferred to the computer every second. The digiBASE is equipped with a buffer that
can hold 128,000 conversions. In order to retrieve all of the list data, the computer must read the
data from the digiBASE before the buffer fills up. In this example, the computer must read data
from the digiBASE at least once every 12.8 seconds to avoid overflow. In practice, the computer
must read more often than this because of the time required for data transfer.
The USB interface is also a limiting factor in throughput. The USB interface is capable of trans-
ferring 12M bits per second. In practice, overhead uses about 25% of the bandwidth so the USB
bandwidth is approximately 9M bits per second. In our example, 320K bits per second must be
transmitted, so the USB has more than enough capacity. If, however, multiple digiBASEs are in
use simultaneously, they must all share the 12M bps. Therefore, no more than 9M/320K =
28 units can be supported at the 10kcps average data rate. This maximum also depends on the
speed of the computer and the efficiency of the software that is emptying the digiBASE buffers.
Any other peripherals on the USB bus will further reduce the maximum throughput of the
system.
A.3. Sample Data Collection Application
This section shows a simple Microsoft
®
Visual Basic program that transfers list mode data from
a digiBASE to the hard disk. The program was written with Visual Basic 6.0, and uses the
Programmer’s Toolkit.
A.3.1. ORTEC Connections Programmer’s Toolkit (A11-BW)
The Programmer’s Toolkit is a collection of ActiveX
®
controls that simplify communication
with an ORTEC MCB. See the Toolkit user’s manual for complete information on how to install
and use the software. The remainder of this note assumes the reader has access to the manual.
A.3.2. Operation of the List Mode Data Collection Program
First, the operation of the program will be described and then the code itself will be described in
detail. When the program is launched, a dialog box similar to Fig. 17 will be displayed.
The column on the left lists all of the digiBASEs found on the system. To collect data, one or
more digiBASEs must be selected by marking the checkbox next to the unit’s name. Once the
digiBASE has been selected, click the
Start
button to begin acquisition. The program will start
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Summary of Contents for ORTEC digiBASE
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