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PCI board comprises quiet high-resolution DAQ plug-in

Posted: 26 Jul 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Alex Mendelsohn?

While Data Translation's comprehensive press release underscores the PCI 2.0-compatible DT3034's accuracy, it's also significant that all data-acquisition (DAQ) sub-systems on this board can operate simultaneously without data loss.

Due to an on-board Data Translation-derived PCI bus interface chip, the 16-bit board uses bus mastering to transfer data to your host PC. Using a dedicated block of memory in the PC, the board performs bus-master data transfers without host processor intervention.

Synchronous I/O
In operation, you can also trigger the system's analog inputs to run synchronously with its analog outputs. That's done with an analog threshold trigger or a digital trigger that's dedicated to the system's DACs.

Moreover, the DT3034's analog-input sub-system can run concurrently with the board's analog-output sub-system. That can be a useful feature if you're running a test that requires simultaneous stimulus and response, for example.

Many triggering modes
The DT3034 gives you a number of triggering modes, including pre-trigger, post-trigger, and about-trigger modes. The post-trigger mode lets you acquire data after a hardware or software trigger. Pre-triggering lets you start an acquisition until a given hardware trigger occurs.

Data can be acquired both before and after a hardware trigger using the about-trigger mode. Either an analog or digital signal can be used as the trigger. An analog trigger can come from an input pin, or any of the analog inputs can be designated as the trigger input. Analog inputs (and analog outputs) can also be paced using an internal or an external clock.

Low noise, high accuracy
Back to Data Translation's claims for all-out accuracy and performance. For starters, all analog and digital connections are separate. Analog I/O is brought out to a dedicated 50-pin connector. Digital I/O is made through a separate 68-pin connector.

The DT-3034 also provides high dynamic range, low noise, and low drift. Its spec sheet shows a signal-to-noise ratio of 100dB.

Full-scale (FS) ystem accuracy for unity gain is specified at 0.01 percent. FS accuracy at gains of 2 and 4 is 0.02 percent. Accuracy at a gain of 8 degrades to only 0.03 percent. Data converter INL (integral non-linearity) is 2LSBs. DNL (differential non-linearity) is within 0.75LSB (with no missing codes).

The press statement notes that the system ensures a worst case ENOB (effective number of bits) of 14.2 bits, along with that SFDR (spurious-free dynamic range) of 100dB. Since this is a worst case spec, under normal conditions you'll likely experience a better ENOB.

In use, you can operate a DT3034 board with either 32 single-ended channels, or 16 differential. The board is software-selectable for uni-polar or bi-polar operation. You can also software-select gain in scope-like increments from unity through 2, 4, or 8. Uni-polar input ranges can span 0-.25V, 0-2.5V, 0-5V or 0-10V.

In bi-polar mode, the front-end gives you 1.25-, 2.5-, 5- and 10V ranges. What's more, single-ended inputs can be referenced to a common point other than ground. That gives you 32 pseudo-differential inputs, too.

Channel gain list
You can also compile a channel gain list. The 1024-location list lets you sample non-sequential channels, as well as channels with different gain settings. A single value can be acquired from any channel, or a number of samples can be acquired from multiple channels.

A multi-channel acquisition is performed by loading the channel gain list and then cycling through it continuously, or until a specific number of samples is acquired.

Using the supplied software, you specify channels in the order you want to sample them. The analog-input channel list corresponds to a channel list FIFO on the board. The channels are read in order (using a continuously-paced scan mode or a triggered scan mode) from the first entry to the last entry in the list.

Cycling through
The board can read the channels in the channel list up to 256 times/trigger, for a total of 262,144 samples/trigger using a triggered scan mode. The channel-gain list can also be cycled through up to 256 times/trigger in a re-trigger mode. That lets you acquire a waveform of data/channel for each trigger (up to 256-ksamples/trigger).

Triggered scanning can also let a DT3034 scan through a list of channels speed with a programmed interval between scans, emulating a simultaneous sample-and-hold function. An internal or external clock can be used to pace the acquisition.

To run this board, or multiple synchronized DT3034 boards, your PC will need to run an Intel 80486, or a Pentium or Pentium-compatible processor, and run Windows 2000 or Windows XP. You'll also need at least 32Mbytes of DRAM. Your color display should be VGA-compatible, with at least 640 x 480-pixel resolution.

- Alex Mendelsohn
eeProductCenter




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