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FireWire-Based Data-Acq System Mates With Notebook PCs

The manufacturer says . . .

ChipCenter's Alex Mendelsohn says . . .

New IEEE-1394 Data-Acquisition Device Delivers Portable, High-Speed 16-Bit Measurements National Instruments extended its high-performance 16-bit NI 6052E data-acquisition (DAQ) family to portable applications with the introduction of the DAQPad-6052E for IEEE-1394. This device uses the NI E Series data-acquisition hardware architecture to deliver 16 single-ended or eight differential channels, a 333 kssamples/s continuous sampling rate, and 16-bit resolution. The device also features two 16-bit analog outputs (333 ksamples/s update rate), two 24-bit counter/timers, and eight digital I/O lines. Its IEEE-1394 (FireWire) connection delivers high-speed, continuous transfers to and from the computer. Engineers and scientists can daisy-chain up to four of the devices on the same IEEE-1394 bus with no degradation in performance. The speed, performance, and portability of the device make it ideal for design validation and research/lab automation applications including acoustical testing, field diagnostics, and vibration analysis. With the release of the DAQPad-6052E device, combined with NI's DAQPad-6070E device, the company offers its two highest performance E Series DAQ products in a portable platform. The DAQPad-6052E for IEEE-1394 is available in a mass-termination model and a BNC-termination model. The mass-termination model features a 68-pin cable that connects to standard E Series accessories such as connector blocks and signal-conditioning modules. The BNC-termination model features BNC connectors to easily attach signals to the device. Engineers and scientists should use the BNC-termination model when no signal conditioning is required on their input signals. The DAQPad-6052E device comes with NI-DAQ 6.9 driver software, a powerful application programming interface for use with numerous development environments and languages. NI-DAQ 6.9 transparently connects to the IEEE-1394 bus interface and integrates seamlessly with NI's popular application software, including LabView and Measurement Studio.

Although nothing is said about it in National instruments's press release, these DAQPad-6052E boxes are essentially hot-pluggable. Sans DIP switches and jumpers, the 400 Mbits/s FireWire hardware and protocol automatically assign your host PC's resources. You can connect one of these systems to any 1394 port—without turning the PC off and re-booting. When plugged in, the PC's software queries the instrument and allocates the required resources. The operating system then enables the instrument for operation. You could conceivably hot-plug up to 64 DAQ Series devices into a single PC using IEEE-1394 busing (although it's likely you'd run out of bus bandwidth). NI's press release discusses portability, and you can see from the photo above that the system complements a notebook PC. Like any good portable system, the DAQPad-6052E can be powered by almost any DC source—even power pulled form an automobile's cigarette-lighter socket. The FireWire DAQPad-6052E will work on any 20 W supply that can deliver between 9 V and 25 V. Although it comes with a small AC-operated power supply, an optional rechargeable battery pack is also available that can run a DAQPad-6052E on its own for a few hours. Both versions of the DAQPad-6052E—either is priced just below $2,900—are also software-configurable. Providing 250 V of isolation for the host PC, the system relies on National's DAQ-system timing controller chip (the DAQ-STC) for all of its time-related functions. The DAQ-STC provides three timing groups, providing a total of seven 24-bit and three 16-bit counters, with a timing resolution of 50 ns. This makes possible applications such as buffered pulse generation, equivalent time sampling, and seamless sampling rate change. The product also uses the RTSI (Real-Time System Integration) bus to synchronize multiple measurement functions to a common trigger or timing event. The RTSI bus consists of a bus interface and a cable. When RTSI-configured, a system routes timing and trigger signals between several functions on as many as five DAQ devices hosted by one PC. Analog Triggering Speaking of triggering, in addition to software and digital triggering, the DAQPad-6052E also offers analog triggering. You can configure the analog-trigger circuitry to accept either a direct analog input from a pin on the unit's I/O connector, or trigger on a post-gain signal developed at the output of the front-end's programmable gain amplifier stage. The 6052E also interfaces to NI's modular SCXI system so that you can acquire up to 3,072 analog signals from sensors such as thermocouples, RTDs, strain gauges, and voltage and current sources (SCXI is NI's modular instrumentation scheme for accommodating its plug-in DAQ devices). SCXI combines a multiplexed analog and digital backplane, and works with virtually every NI data-acq platform. The Executables In its press statement, NI refers its NI-DAQ v6.9 software. This latest spin of the venerable NI-DAQ software includes a library of functions that let you get to the features of the DAQPad-6052E for IEEE-1394. The software carries out interactions, such as programming interrupts, between the computer and the DAQ hardware. NI-DAQ also has a consistent software interface. If you're already using an earlier version, you can change platforms with few modifications to your code. Whether you use NI's LabView, Measurement Studio, or other higher level applications, the DAQPad-6052E relies on NI-DAQ for a transparent connection to the IEEE-1394 bus. The diagram underscores NI-DAQ's relationship to other system blocks. click for full-size image In the press release, NI mentions the hardware architecture as delivering 16 single-ended or eight differential channels, at a 333 ksamples/s continuous sampling rate with 16-bit resolution. Let's elaborate a bit. The 6052E accepts both unipolar and bipolar signals, with inputs made through an array of BNC connectors on the front panel. Small so-called source switches are flipped manually to connect or disconnect built-in ground reference resistors to establish single-ended or differential operation per channel. In unipolar operation, the input range is established between zero volts and some positive reference voltage, and extends from 0 to 10 V. For bipolar operation, the device has a input range of ± 5 V. A nice feature is that input polarity and range settings can be programmed on a per-channel basis. That lets you configure each input channel independently. The 6052E can also sample its multiple channels at the same maximum rate as the single-channel rate as long as you pay attention to settling time constraints. Software-programmable gain setting is also provided. You can set the front-end gain at 0.5, unity, 2, 5, 10, 20, 50, or 100 to appropriately suit your input transducer needs. As long as you don't over-drive it, that ability lets you enjoy the full resolution of the unit's A/D conversion. The table shows the overall input range and precision you can get based on the input-range configuration and gain settings. Range Config. (V) Gain Actual Input Range (V) Precision (µV) 0 to +10 1.0 0 to +10 153 2.0 0 to +5 76.3 5.0 0 to +2 30.5 10.0 0 to +1 15.3 20.0 0 to +0.5 7.63 50.0 0 to +0.2 3.05 100.0 0 to +0.1 1.53 -5 to +5 0.5 -10 to +10 305 1.0 -5 to +5 153 2.0 -2.5 to +2.5 76.3 5.0 -1 to +1 30.5 10.0 -0.5 to +0.5 15.6 20.0 -0.25 to +0.25 7.63 50.0 -0.1 to +0.1 3.05 100.0 -0.05 to +0.05 1.53 The press release briefly mentions the product's analog output capability. It can develop two channels of voltage at its I/O connector, with both the reference and the range software-configurable. The reference can be either internal or external, and the range can be either bi- or unipolar. Special analog-output re-glitch circuits are also built in to ensure uniform glitch energy. NI's re-glitch scheme doesn't eliminate glitches from the system's output D/A converter, but it makes them uniform in size. Automatic Calibration NI also ships these instruments factory-calibrated, with the calibration constants required to feed the system's calibration D/A converters stored in EEPROM; the D/A converters themselves have no on-chip nonvolatile memory. The NI-DAQ software determines to load cal constants if necessary, and an onboard calibration reference ensures the accuracy of self-calibration. When NI-DAQ performs calibration, it automatically loads the EEPROM constants, a process that takes less than a minute. If you don't use NI-DAQ, you have to load these values manually. The EEPROM contains a user-modifiable calibration area. In any case, the product can measure and correct for almost all of its calibration-related errors—without any external signal connections. The table shows the relative and absolute accuracy specs for the product. click for full-size table As a low-profile package that can fit under a laptop, these products should lend themselves to applications where portability as well as the ability to speedily connect them to sensors is significant. As such, I can see them being used for things such as in-vehicle automotive testing, for example. The BNC version, in particular, would let you quickly connect and disconnect signal lines, which could come in handy in vehicular testing scenarios where you'd likely want to move your data-acq and processing bundle from vehicle to vehicle and/or from vehicle to lab.

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