Distributed data-acquisition system

Introduction
ECN-Engineering & Services has developed a modular, distributed data-acquisition system. The system is rugged, yet flexible, and ready for measurements in harsh environments.

Front-end system (19 inch CpU- and instrumentation rack)

Specifications signal conversion modules:

• The analogue input module contains a carrier for commercially available 5b-modules
• input modules are available for strain gauges, voltage, current, frequency, Lonworks telemetric system, quadrature input
• Max. 128 Hz sample rate, analogue bandwidth 20 Hz
• Resolution: 12 bit resolution (option: >12 bits)
• auxiliary power supply available for external sensor-devices
• inputs and power supply are mutually isolated on all inputs
• Custom-made modules on request
• The system fully complies to the industrial immunity standard EN 50082-2 according to: - EN 61000-4-2 (electrostatic discharge test) - EN 61000-4-5 (surge test) - EN 61000-4-3 (radiated RF test)

Signal conditioning and aD-conversion module

Features:

• Distributed architecture, many front ends can be connected with many hosts
• Time synchronous measuring of all sampled signals at 128 samples per second
• Local signal-conditioning and analogue-to-digital conversion (max. 16 modules and 32 channels)
• User friendly installation: simple network configuration, hot swappable modules, fault tolerant installation of sensors and input modules
• integrated glas fibre network-interface
• Lonworks RF-interface for interfacing with a self-contained rotating sub-system
• Open system-architecture, host-frontend communication based on TCp/ip network socket connections

Installation
installation of the data-acquisition system is quite simple. at each physical location where sensors must be installed, a front-end system will be placed. For each sensor, a dedicated signal conditioning & analog-to-digital-conversion module will be installed in the front-end, up to a maximum of 16.

The following sensor-conversion modules are available based on standard 5b modules which can be inserted on the standard analog input-module:

• strain gauges
• rotary encoders
• anemometers
• wind vanes
• temperature sensors
• accelerometers, etc.
• Lonworks interface for the ECN rotating telemetric measuring system

Network configuration
Front end systems and host computers are interconnected with optical fibers or standard UTp cable (Tbase10/100). Network-configuration is accomplished by filling in a text-file describing the ip-addresses and channel-numbers of each front end.

At this moment a maximum of 16 front-ends and 1 to 4 hosts can form one integrated data-acquisition system, only limited by the throughput of the network and performance of the host-computer.

A separate node or a front end system serves as a master-clock.

Example of a simple configuration

Protection/signal conditioning/interfacing
Input protection is integrated in the front-cover of the front end box. all connected wires (including the power supply) are protected. Each individual sensing-device is connected with analog or digital input module. For 'standard' signals, a standard 5b module converts the sensor signal, after which the signal passes a 20 Hz low-pass phase linear anti-aliasing filter. after passing the anti-aliasing filter, the signal is digitized (12 bits) with a sample rate of 128 Hz.

Front end & instrumentation interface
Windows CE3.0 is used as real time OS in the front end system. Data is stored into a local circular buffer thus providing a buffer-mechanism to serve any asynchronous and concurrent requests from the hosts. an internal crystal-based controllable clock provides a platform to synchronise all front end-clocks on the network.

The instrumentation-adapter it is based on the industry standard iSa/pC104. The communication interface is open and quite strait forward to be integrated within any host environment. Communication between input-modules and front end CpU is based on a subset of the iEEE1454 standard.

Host api
The standard system is delivered with an host-api for Windows NT/2000. Sample-code for Labview is available.

Contact: Klaas Berkhof (+31 22 456 4225)