Simplifying the set-up of large channel count DAQ systems
A major challenge facing engineers is the need to make the setting up of any data acquisition (DAQ) system more efficient since the time spent in this initial phase is effectively down time. This is particularly important where the DAQ system and workflow involves large channel counts. This White Paper aims to demonstrate the advantages of simplifying large channel counts in applications such as structural testing to reduce the time spent on setting up a system.
There are four key areas that need to be carefully considered when setting up a DAQ system for the acquisition of large channel counts. These are:
1. Configuration process
There are three distinct stages to the configuration process. The first is to plan and design the test so that the general outcomes can be considered ensuring that the sensors are correctly defined to accurately capture the required data. Aspects that need to be considered at this stage are which components need to be tested and whether the primary aim of the test is to examine either static or dynamic loading or the durability of the structure. This involves defining the broad scope of the load spectrum and looking at the likely parameter ranges that need to be captured.
The second stage is to define the test by clarifying what sensors – such as strain, displacement, load, and temperature – will be required and where on the structure these can be best placed to accurately capture data that is representative of the parameters in that component without impacting negatively on the structure’s functionality. Following on from this careful consideration needs to be given as to how the sensors will be wired and how the wiring can best be fixed to the structure or individual component. This stage also demands that the network and power infrastructure is considered to ensure it will meet the test demands.
The final stage of the configuration process is to more accurately define the configuration parameters. This includes evaluating the expected parameter test values and ensuring that the transducers are properly calibrated.
2. Data sources
Structural testing requires that data be gathered from a wide range of sources that are involved with the project. Each of these has different requirements and these can sometimes clash which may need to be carefully considered when making any final decision on the DAQ set-up
The design department usually has an important part to play in any structural testing since it is responsible for the design and identification of the different sensors that will be needed for the tests. The design department may also have a view on where the different sensors need to be placed to ensure optimum data capture.
A factor that needs careful consideration during the initial planning phase is the expected values of sensors during test operations. For example, the possible strain at 100% load will impact on the specifications so that the correct sensor is selected for the measurement task.
Another department that needs to be involved before any testing takes place is the department responsible for the correct calibration of any instrumentation used. This may simply be supplied data from the vendor that is being used to supply any transducers or sensors but information such as serial numbers and scaling is needed.
All of the names and identification data for any sensors being used need to be included. Such information is usually supplied by the test department and includes sensor data such as gage factor, scaling information, filters and pictures. Other information such as details of the transducers, the channel configuration, test and project settings also need to be available. In short, all the different configuration data has to be included in the DAQ test database and be readily accessible to all parties involved in the testing sequences.
3. Workflow options
Large channel setups can be organized with a variety of different workflow approaches. This White Paper looks at four different approaches, each of which has different advantages and disadvantages. Usually only one is suitable for any given measurement task and a careful evaluation of all of the aspects will help to ensure that the correct choice is made before getting too deeply involved in the measurement mechanics.
a. Manual mapping
Manual mapping is the simplest workflow for measurement tasks. This is achieved by first creating a model of the data acquisition amplifier’s hardware. This usually takes the form of a table. All the parameters for the different sensors – such as name and gauge factor – can be manually entered once the amplifier has been modeled in a table. The system can then be initialized and the measurement tests completed.
The biggest disadvantage of this approach is that engineers need to be very careful not to make any entry mistakes when manually typing in the various parameters. It can take time to troubleshoot a test where manual inputting has been used since each aspect of the table will need to be carefully checked to determine where any errors might be.
b. Wiring-based mapping
The second approach is for engineers to develop wire-based mapping by creating a test point plan database and merging this with the preferred hardware set-up database. This is an independent two-stage process since the test point plan can be created either before or after the configuration of the acquisition hardware is established.
The result of merge procedure is a wiring diagram that allows engineers to connect each channel. An advantage of this approach is that the sensor data is embedded in the test point plan meaning that there is no need to manually input any data.
The input of all test specific transducers and strain gage parameters can be done before any testing starts so that the set-up process can be expedited. In this method various groups of channels can be defined to facilitate working with large channel counts.
During the merge procedure the status can be verified of merging the two databases – the test point plan database and the data acquisition database – that checks if all the channels can be correctly connected. The test is then ready to run.
c. Identity-based mapping
Increasingly the use of transducer identification technology (T-ID) can facilitate the import of the transducer data into the database. T-ID works by ensuring that each transducer has a unique 8-byte number that is stored in a chip/ROM and included in the measurement chain. The transducer data can easily be read by a USB dongle using a 1-wire adapter and saved directly as an Excel spreadsheet.
In this approach the T-ID code becomes part of the test database to simplify the creation of the test point plan once the channels are correctly connected to the DAQ hardware system. All settings are imported automatically without any need to manually type in the numbers and parameters. This method makes it much quicker than either the manual or wiring-based approaches to initialize the hardware and run the DAQ tests.
d. TEDS set-up
A more advanced approach than the T-ID method is where all of the transducer data is stored directly on the transducer, or on a connector, in an electronic datasheet on an EEPROM chip. This transducer electronic datasheet (TEDS) approach means that the required information is read and the channels automatically set-up according to the TEDS setting.
This method can be used with a 1-wire protocol to communicate between DAQ system and the TEDS chip. TEDS information must conform to an IEEE standard that allows different templates and languages to be used for the information
Various Workflow Options
The various different workflow options are shown in the table below in order of increased confidence and certainty.
| || |
| || |
Identity- based Mapping
| || |
| || |
4. Configuration verification
The final check before starting any DAQ tests is to verify the configuration. A channel configuration that is clearly arranged ensures that mistakes and confusion are avoided. It is important to consider the capabilities of the selected DAQ hardware at this stage. For example, HBM’s catman® Enterprise has software tools to easily and rapidly check the configuration and data validation.
Wiring checks should also be undertaken as a matter of course since these increase confidence in the overall set-up. Wiring checks can allow a shunt comparison by contrasting the nominal shunt reading with the measured shunt reading with a single mouse click. This can easily indicate whether any sensor is problematic because of, for example, a broken wire.
When looking to simplify the set-up of a large channel count DAQ system for structural testing there are a few important points to bear in mind. The data exchange should be flexible and reliable. On this basis using data that has to be manually input should be avoided as far as possible. The use of T-IDs and TEDS technology increases the safety and reliability of set-up and configuration. Similarly the use of automated channel and wiring check functions is a valuable aid to setting up large channel count systems. It is also more efficient if the DAQ system facilitates import and export functions and enables automatic channel assignment.
HBM has many years of expertise across a wide range of different applications including static wing tests with a number of different aircraft manufacturers and has been heavily involved in the testing and development of modern, effective blades for wind turbines. In addition to working with different structures, HBM’s engineers have been involved with instructional testing as well as functional and performance testing and monitoring of a wide range of applications.
HBM is constantly developing new products that are designed to facilitate rapid testing while boosting test efficiency. In addition HBM is committed to maximizing test reliability and accuracy so as to provide highly accurate data on component verification and product life cycle. The company’s product range includes supplying the whole of the measurement chain from the sensors through to software for comprehensive data analysis.
It can supply a variety of different systems, including bespoke systems for specific testing requirements, which facilitate centralized and decentralized setup as required by the client.
HBM’s data acquisition hardware s supports all relevant functions needed to data acquisition on large channel count tests. This also includes the capability to interface to control systems. HBM has also developed professional software that simplifies the design, analysis and data management.