Offering no less than 20 new products, all introduced in a family at the same time, National Instruments (NI---Austin, Texas) is rolling out what it bills as the next generation of multi-function data acquisition (DAQ) products. Significantly, they use the company's newly designed NI-STC 2 system controller chip and a new NI-PGIA 2 amplifier (composed of a family of discrete components).
Dubbed the M Series, these multi-function DAQ boards offer better accuracy than predecessors, as well as faster sampling rates, more I/O channels, and a set of expanded features. The 20 new devices themselves address low-cost, high-performance and high-accuracy applications.
Many I/O Channels
Operationally, M Series DAQ devices offer up to a whopping 32 18-bit analog input channels, four 16-bit analog outputs, two 32-bit counter/timers, and plenty of digital I/O lines (48 lines). You can use these devices to hardware-time up to 32 of the digital lines up to 10 MHz.
NI also claims its M Series will not only lower the cost per I/O channel by more than 30%, but they will also reduce overall system costs by minimizing set-up times. That's accomplished using tools included in NI's NI-DAQmx measurement services driver software. NI-DAQmx software also provides a programming interface for NI's popular LabVIEW, Visual Studio .NET, and LabWindows/CVI.
"In the ten years since the introduction of our E Series multi-function DAQ devices, we've collected feedback from thousands of data acquisition users," notes Tim Dehne, NI's senior VP of research and development.
"The result is that our new M Series product line has significant enhancements compared to the E Series," says Dehne.
Dehne also emphasizes how the NI-STC 2 chip now consolidates several discrete ICs into a single ASIC. He also says that the NI-PGIA 2 amplifier improves accuracy at a lower price. The NI-STC 2 synchronization and timing controller permits up to six operations to execute simultaneously, at throughput rates up to five times faster than previous DAQ devices.
The NI-STC 2 ASIC provides six DMA (direct memory access) channels with dedicated scatter-gather DMA controllers for each function. It also packs 32-bit counter/timers with encoder compatibility, and is responsible for generating and routing of RTSI (realtime systems integration) bus signals for multi-device synchronization.
The ASIC also handles generation and routing of internal and external timing signals, and uses a PLL (phased locked loop) for clock synchronization.
For their part, the re-designed NI-PGIA 2 family of programmable gain instrumentation amplifiers also reduces settling time, to ensure accurate measurements even at the fastest scanning rates. That's because the settling time of an A/D converter can significantly impact accuracy when scanning multiple channels at fast rates (settling time is the amount of time required for a signal that is being amplified to reach a specified level of accuracy).
If an amplifier doesn't have low enough settling time, the measured signal will be digitized inaccurately. For any given level of resolution (or accuracy), shorter settling times are desirable because they permit faster sampling rates without sacrificing accuracy.
Fast Settling, High Linearity
To ensure accurate measurements, M Series plug-ins using the NI-PGIA 2 optimize tradeoffs between cost, speed, and accuracy. The NI-PGIA 2 on the high-accuracy M Series family is optimized for 18-bit fast settling, low noise, and high linearity.
The NI-PGIA 2 also improves accuracy by minimizing settling time, maintaining specified resolution even at maximum sampling rates. The figure shows the high-speed family NI-PGIA 2 settling to virtually zero error in 1.5-µs following a 20-V step (worst-case scenario).
The M Series also offers what NI says is a "revolutionary design for calibration." Dubbed Mcal, it operates at every input range, improving measurement accuracy by up to five times, in addition to extending the recommended calibration interval on most M Series devices to two years.
Mcal is effective because components such as A/Ds and PGAs (programmable gain amplifiers) suffer from non-linearities and drift due to time and temperature. Compensating for these inherent sources of error requires device self-calibration.
Legacy data acquisition devices used onboard precision voltage references to perform 2-point calibration for a single measurement range. But, that approach failed to protect against localized non-linearity over the range of a data converter, diminishing the measurement accuracy of the device.
Additionally, because the old method calibrated at only a single input range, measurements that scan multiple channels at varying input ranges were limited in accuracy by the tolerance of a resistor network.
Linearization And Cal Engine
On the other hand, M Series products with NI-Mcal rely on NI's patent-pending linearization and calibration engine. It calibrates at thousands of voltage levels and at all input ranges.
MCal uses PWM (pulse width modulation), in conjunction with a high-precision voltage reference to do that. The duty cycle of the PWM is used to vary the voltage level, so self-calibration is done at multiple points. Calibration constants are generated and stored in an EEPROM to model the non-linearity of a board's A/D and correct subsequent measurements.
NI claims that NI-MCal improves measurement accuracy by up to five times when compared to traditional 2-point calibration schemes. Additionally, NI claims that the improved precision reference featured on most M Series devices will lower maintenance costs by increasing recommended calibration intervals from one year to two.
Want more info? Contact National Instruments Corp., 11500 No. Mopac Expwy., Austin, Texas 78759-3504. Phone: (512) 683-0100. Fax: (512) 683-8411. E-mail: firstname.lastname@example.org
Or, visit NI's dedicated DAQ Web pages.