Signal conditioning removes aliasing from samples

Sensor signal conditioning packages for use with data acquisition systems eliminate all aliasing from sampling and can scale up to acquire data for applications with hundreds of inputs.

Microstar Laboratories, maker of Data Acquisition Processor (DAP) boards, has announced sensor signal-conditioning packages with data acquisition systems that eliminate all aliasing from sampling and that scale up to acquire data for applications with hundreds of inputs.

This results from the synergy of three products: first, DAPcell to synchronise data acquisition on networked PCs to within a few nanoseconds; second, iDSC 1816 boards - specialised DAPs that include analogue and digital filters - inside each PC; and third, SCS (Signal Conditioning System) packages in standard industrial enclosures.

DAPcell network software allows any or all PCs on a network to run DAPcell server software to handle requests for data-acquisition services provided by the DAPs on those PCs.

Requests for those services come from DAPcell client software on those PCs or on any other PCs on the network.

This technology avoids network limitations on performance.

For instance, a request for high-speed logging to disk can originate anywhere on the network but typically specifies that the DAPcell server software transfers data to a disk on the same PC: the one containing the DAP that acquires the data.

A hardware option distributes clock signals that allow DAPcell to synchronise sampling across all servers on the network to within a few nanoseconds.

The iDSC 1816 board - a specialised DAP with programmable onboard filter circuits - combines 16bit resolution on eight simultaneous channels of data acquisition with brick-wall anti-alias filters on each channel.

The iDSC 1816 samples analogue inputs at a throughput of 1.2Msample/s with a sampling rate on each channel that can range from 8sample/s to 153.6Ksample/s.

The data stream optionally includes an additional 300Ksample/s: information from one or two external timing channels.

Software can parse the data stream to correlate the analogue data with events on one or both of the timing channels, to a resolution of 51ns.

DAPstudio, a Windows measurement-software application, includes a filter-design option that displays the filter-response curve in real time as you move onscreen sliders to customise the filter on each channel.

An SCS package provides direct connection to sensors, and offers many signal-conditioning services in a single convenient, powerful package.

These include: current sensor excitation: 4mA at 28V; voltage sensor excitation: 1, 2, 5, and 10V up to 70 mA; quarter-, half-, and full-bridge resistor networks; 120 and 350Ohm resistors as standard options; any value resistor networks, sensor by sensor; 10 full-scale options: 10, 20, 50, 100, 200 and 500mV, and 1, 2, 5, and 10V; available offset ranges from between +/-0.5V to +/-5V, depending on input option range used; programmable gain with auto-calibration; programmable AC/DC coupling for ICP sensors; and two high-resolution acquisition-synchronised timing channels per module.

Each SCS package consists of an MSIE standard industrial enclosure containing one, two three or four modules.

Each module connects to an iDSC 1816 contained in a PC and provides it with eight conditioned analogue signals and up to two TTL timing signals.

The data stream produced by each iDSC in a PC optionally includes one or two time stamps for each set of eight converted signal samples.

The time stamps give the clock count when the iDSC sensed a rising TTL edge during the analogue-to-digital conversion process.

You can use 8-, 16-, or 32-channel building blocks to generate alias-free synchronised data from raw signals at the sensor in applications that can span hundreds of channels sampled simultaneously.

And you can do all this at a very reasonable cost: around US $1000 per channel, excluding the cost of PCs.

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