Gigabit-Ethernet Dynamic Data Acquisition

Dynamic data acquisition systems are met with ever-increasing demands. One example: A state-of-the-art gas turbine test stand requires data to be measured on more than 300 dynamic channels with sample rates up to 50 kHz per channel. For highly complex and demanding measuring tasks like this, LTT Tasler has developed a new distributed concept based on Gigabit Ethernet technology where any number of data acquisition front-ends, monitoring and storing clients are networked with each other.

Distributed acquisition and processing of sensor signals is provided by 10 front-end systems Type LTT180-32 SensorCorder, each with 32 galvanic isolated input channels including integrated ‘all-in-one’ conditioning for Volt, Strain Gauge and ICP inputs. The Strain Gauge mode supports full-, half- and quarter-bridge connections. Optional supply of constant current allows very precise and low-noise Strain Gauge measurements for high-temperature applications. The connections of the respective sensors are software configured – no hardware modification is required.

Centralised network management ensures that each front-end in the network receives the necessary bandwidth for data transfer on the active measurement channels. The flow of measured data from the front-ends to the monitoring and storing client is based on secured broadcast transfer. This allows multiple monitoring and storing clients to receive the data flow from a particular front-end system simultaneously. Each unit can independently display, store or process selected measurement channels. This allows, for example, distributing high numbers of channels across several online displays. Similar applies to the backup of measured data. Here, the network load is almost independent from the number of processing units.

The major benefits of using distributed digital networks are considerably reduced cabling requirements and less interference. The length of analogue cables from the sensor to the respective front-end – being susceptible to pick up stray signals – can be kept relatively short. On the other hand, the digital data transfer is performed via a single, more insensitive Ethernet cable, possibly a fibre optic cable. Longer distances (typical up to 100 meters) between test object and processing units can be handled trouble-free and without data loss. Further, using independent monitoring clients allows users to integrate their own software packages via the provided API.

Application report: LTT's SensorCorder at the gas turbine test stand of Siemens Power Generation