2 CD 198 and 4 SC 198 Units under test at 150 g
The CDAQS Centrifuge Data Acquisition System was developed by CARRACK in conjunction with the Geotechnical Centrifuge Centre at Cambridge University to meet their need for multichannel digital acquisition for the measurement of pressure and acceleration in both structural and earthquake models at up to 150 g on the Cambridge 10m beam centrifuge. Early versions are also in use in the US Army Centrifuge complex. A 64 channel dual CDAQS system was developed for the Broadbent Geotechnical Drum Centrifuge with 32 channels on the main drum and 32 channels on the independently moving toolplate. This system is being used successfully by Toyo Construction Co., Japan. A recent paper by Prof. Schofield gives details of geotechnical Centrifuge techniques.
The single CDAQS system consists of a PC running a terminal program, connected to a CD_IF 198 Interface Module in the laboratory. A cable carrying power, communication and trigger signals connects via a minimum of 8 sliprings to the CDAQS CD 198 Acquisition Module on the rotating unit. The acquisition module is connected to two SC 198 Signal Conditioning Modules, each with connections for up to 16 transducers. Data can be acquired at up to 5000 samples per second simultaneously on all 32 channels, and is stored in memory for upload at the end of the test.
The dual CDAQS configuration uses a dual Interface Module CD_IF 198/2 that connects to two CD 198 Acquisition Modules. Where there are two independent parts to the centrifuge, as in the Broadbent Drum configuration, each CD 198 is connected via a separate slipring assembly. On a Beam centrifuge with a single rotating element both CD 198 Modules use a single set of sliprings with shared power connections, requiring a minimum of 12 sliprings, although more improve reliability.
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| Number of channels | 32 |
| Simultaneous sampling rate | 1 to 5000 samples s-1 |
| Sample resolution | 16 bits |
| Input sensitivity | ±10 V |
| Data buffer capacity (samples) | 1,000,000 |
| Communications | duplex RS485 |
| Comms rate | 19200 baud |
| Power required | ±15 V |
| Power consumption (max) | 50 W |
| Trigger source | 5 V pulse or via keyboard |
| Slipring requirements (min) | 8 |
| Size | 120 mm × 225 mm × 100 mm |
| Weight | 2.4 kg |
| Rating | IP65 |
(2 required per 32 channel system)
| Number of channels per unit | 16 |
| Amplifier gain | 1,10,100,1000 |
| Input impedance | 1 Mohm |
| Transducer excitation | 5 or 10 V |
| Filtering:- Low Pass | Off or 500 Hz |
| Filter rolloff | 12 dB octave-1 |
| Size | 120 mm × 225 mm × 100 mm |
| Weight | 2.2 kg |
| Rating | IP65 |
| Transducer connectors | 62GB 56T 08 04P |
The Signal Conditioning Modules can be designed to match any required transducers.
2 CD 198 and 4 SC 198 Units under test at 150 g
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The CDAQS system is continuously evolving, both in response to current users' requirements and to accommodate new applications. There are several exciting developments in the pipeline, which will be available in the next few months.
We are developing alternative communication links between the laboratory based unit and the rotating elements to minimise the number of sliprings needed. We shall be offering a choice of either a reduced slipring count (6 rings) with a conventional, wired serial connection or the option of an infra-red link between stationary and rotating components. With the infra-red link, there will be the option of powering the unit from rechargeable batteries on the rotating element -- giving the possibility of a system without sliprings.
Our users want to be able to see data in real time during experiments, and we plan to integrate the CDAQS System into a complete WINDOWS environment with full display facilities and a real time link to a full mathematical analysis package. This exciting development will require a substantial investment in software development, but we believe that it will give us an unbeatable Data Acquisition System.
The new generation of very high g Drum Centrifuges calls for a major re-evaluation of the physical design and mounting of the Acquisition systems, and we are currently reviewing the options. In these very high g environments, there is a considerable benefit to be had from miniaturisation, especially in cabling and connectors, and this area will be receiving attention in future systems.
CARRACK is committed to supporting existing and new clients in the business of collecting data from centrifuge experiments, and is happy to consider your particular requirements.
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e-mail: sales@carrack.co.uk