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Nifty mini data-acq pods talk USB

Posted: 25 Jan 2005 ?? ?Print Version ?Bookmark and Share

Keywords:usb? . national instruments? ni? data-acquisition? daq?

The USB juggernaut continues. In 2004, National Instruments (NI) introduced quite a number of data-acquisition (DAQ) devices using USB.

Its more-or-less plug-and-play USB DAQ products ensured relatively pain-free connectivity at set-up, hot-pluggability, and a high degree of portability. Short configuration times were also a bonus. These new pods continue the trend at NI.

Prior to those 2004 DAQ product roll-outs, however, we looked at some USB data-acq pods from Measurement Computing Corp. and LabJack Corp. that were almost identical to each other (in fact, LabJack claimed Measurement Computing "borrowed its design").

The 1.2KS/s LabJack pod, with its 12bit ADCs, screw-type terminal connections, and multiple DAC outputs, was priced at about $120 with software, thus it was in the same class as Measurement Computing's PMD-1208LS and PMD-1024LS. Both were supported under Windows OSes. Both communicated with a host PC over USB, and at the same time, were powered by USB.

The 1.2KS/s beasts
Also, like NI's latest pods, these earlier pods offered analog and digital I/O, and were compatible with USB v1.1 as well as high-speed USB 2.0. Providing eight single-ended or four differential analog inputs with 12-bit resolution, the PMD-1208LS, for example, provided sample rates up to 1.2KS/s, and had eight software-selectable input ranges.

In addition to the analog inputs, the unit had two channels of 10bit analog output, one 32bit counter, and 16 bits of digital I/O. It was priced a tad less than LabJack's wares.

Kicking it up a notch
NI's latest products kick USB portable pods up a notch. As a 12Mbps full-speed USB 2.0 pod, the USB-6008 is a 12-bit resolution (in differential mode; 11 bits with single-ended conversion) 10ksps device, but its cousin, the USB-6009, which is also USB 2.0 compatible, digitizes at speeds to 48KS/s at 14 bits of resolution (in differential mode; 13 bits for single-ended operation).

Both pods are USB powered, pulling about 80mA in normal operation (0.5A max.). They're also power-managed, dropping to 500?A maximum in USB Suspend mode.

Multi-channel data conversion
The pods' successive-approximation ADCs, backed by 512byte FIFOs, can accommodate eight high-Z channels of single-ended signals, or four channels of differential inputs.

The single-ended inputs can handle as much as 10V signals.

In differential operation, ranges include 1V, 1.25V, 2V, 2.5V, 4V, 5V, 10V or 20V. It's kind of nifty to see those unusual intermediate 1.25V, 2.5V and 4V ranges in there, in addition to the usual scope-like decades.

More good specs: timing resolution is 41.67ns, with a timing accuracy spec of 100ppm of the actual sample rate.

As for triggering, it can be obtained from either external hardware under test, or from your applications software.

Digital I/O, too
Both pods also pack 12 lines of three-statable digital I/O that's TTL-compatible, LVTTL-compatible, and CMOS-compatible. Each I/O channel is also individually bi-directionally programmable. Finally, both pods have 32bit-resolution 5MHz event counter aboard.

On the dual-channel analog output side, which uses successive approximation 12bit resolution DACs slewing at up to 1V/?s, you can expect an absolute accuracy (no load) of 7mV (typ.), or 36.4mV (max.) at full scale. The maximum update rate is software-timed at 150Hz, and the DAC channels can develop up to 5V signals, delivering as much as 5mA into 50? loads. These outputs are also capable of delivering 50mA into shorted loads, if need be.

Software support
Both of NI's new DAQ pods are also supported for use with Windows 2000 and Windows XP, as well as Mac OS X, and Linux OSes. The company's press release mentions the ready-to-run data-logging software, and the bundled NI-DAQmx Base measurement services driver software for programming in NI's LabVIEW graphical programming environment, or in C. The ready-to-run data logger application acquires and logs up to eight channels of analog data.

For its part, NI-DAQmx Base software is a multi-platform driver with a subset of the NI-DAQmx programming interface. It can be used to develop custom DAQ applications in either LabVIEW or C.

Students are welcomed here
Finally, the press statement notes that both of these new data-acq devices ship with freebie data-logging software. What's more, unlike some companies that don't seem too friendly to engineering and science students, NI encourages student usage of these products. Indeed, NI offers special USB-6008 and USB-6009 student kits.

These kits give students personal low-cost hands-on learning tools. Both USB-6008 student-kit 779320-22 and USB-6009 student-kit 779321-22 include LabVIEW Student Edition, NI-DAQmx Base Software, NI-Ready-to-Run Data Logger Software and a USB cable.

- Alex Mendelsohn
eeProductCenter




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