DAQ software enables interactive filter design

You can now design filters that roll off at better than 96dB/quarter-octave, and play on dedicated hardware. The latest version of DAPstudio measurement software from Microstar Laboratories, maker of Data Acquisition Processor (DAP) boards, lets you do this, as well as build and run applications based on the company's Signal Conditioning System (SCS) Series of hardware platforms. No other data acquisition software is required.

In use, an SCS would connect directly to your sensors and to one or more specialized iDSC 1816 DAPboards installed in a PC. This would give you as many channels as you need of filtered 16bit resolution DAQ, with inputs from ±10mV to ±10V.

Cost-effective DAQ
SCS/iDSC hardware costs—excluding the PC—range from about $1,000/channel. The DAPstudio software itself is less than $200, and you can download the full version for a free trial, and use it—without hardware—to view any binary data files and to design filters.

Field-proven SCS Series hardware connects directly to sensors and to one or more DAP boards. That gives you as many channels as you need of filtered 16bit-resolution simultaneously-sampled data, logged directly to disk.

Commercially available off-the-shelf PCs and associated disk controllers and drives have enough electrical power and sufficient computing horsepower for a single PC to form a balanced network node with four iDSC 1816 boards and an SCS-32. Such a node can continuously log to disk all 32 channels of conditioned anti-aliased data, at a DAQ rate of 153.6KSps/channel. That's an overall rate of just under 5MSps.

An additional synchronization board in each PC will let you set up a number of PCs on a network to work as a single synchronized system. You can configure those to support as many channels as you need.

Signal conditioning
An SCS package provides direct connection to sensors. It also provides signal-conditioning services in one package. These include current sensor excitation (4mA at up to 28V), and voltage sensor excitation (1-, 2-, 5-, and 10V at up to 70mA).

The SCS services also support quarter-, half-, and full-bridge resistor networks, with 120-ohm and 350-ohm resistors as standard options, and support for any value resistor networks.

The system also works on a sensor by sensor basis, with ten FS (full-scale) options; you get 10-, 20-, 50-, 100-, 200-, 500mV, and 1-, 2-, 5- and 10V FS ranges. The system also accommodates offset ranges from between ±0.5V to ±5V, depending on the input option range used.

The system also provides programmability of gain, with auto-calibration, and programmable AC/DC coupling for integrated circuit piezoelectric (ICP) sensors, and two high-resolution acquisition-synchronized timing channels per iDSC1816.

Analog filtering
Before a signal reaches the A/D (analog-to-digital) conversion stage on an iDSC1816 board, it passes through an analog filter, one on each channel, that takes out all frequencies above the Nyquist frequency. The subsequent digital waveform is therefore free of any alias frequencies that otherwise would corrupt the data.

On-board intelligence directs DSP of the waveforms corresponding to filter designs you create interactively with DAPstudio. Valid cutoff frequencies fall in the range of 2 percent to 80 percent of Nyquist. Above 50 percent of Nyquist, resulting filters roll off at better than the stated 96dB/quarter-octave.

Microstar also offers a CD that contains all software and hardware manuals for all products, including DAPstudio. You can also order demonstration hardware for free, unless you decide to keep it.

- Alex Mendelsohn
eeProductCenter