Boarding the DAQ bus
28 Nov 2006
DAQ is finding a broad range of new users among plant engineers
Data acquisition (DAQ) is finding a broad range of new users among plant engineers as a result of continuing advances in performance, ease of use and installation, as well, of course, as lower cost. The trend covers technologies both at the volume end of the market and in highly specialised areas.
Among the key enabling technologies behind these trends is USB (Universal Serial Bus) — originally introduced as a low-speed peripheral bus, but now being used increasingly to support high-speed DAQ in a broad range of applications.
Plug-and-play installation of USB peripherals is a particular attraction of this computer interface technology, as it means that DAQ users no longer have to set up and configure the hardware to use it. Also, USB handles data streams in logical channels, called 'pipes', that form a logical connection from a hardware channel to an application, further simplifying setup and ensuring that data automatically travels to the right destination.
"It is so much easier to get the devices up and running, while the cost has come down as well," comments Ian Bell marketing manager, National Instruments UK and Ireland. "Fundamentally, you can deliver the same performance with a USB external pod in terms of accuracy and measurements as you can with a plug-in card." However, he added, when you get up to the limits in terms of speed, then a PCI Express card is always going to be faster.
USB is now commonly used to enable process engineers do some quick data logging so that they can analyse an issue. Engineers, for example, typically plant a laptop down next to a machine, plug in a USB DAQ device and then plug in some sensors, like vibration or temperature sensors.
"In some companies it has become practical for every process engineer or every maintenance engineer who has a laptop to also have one of these little data acquisition pods as part of their toolkit," said Bell. In effect, he added, there is now "a new class of users, which you might class as a more casual data acquisition users, who don't want to have to do programming or want to have programming that is very easy to use."
The evolution of easy-to-use USB DAQ plus off-the-shelf, read-to-run software then it makes it possible for people who are not necessarily engineer qualified, software engineers or programmers to be able to acquire data, continued Bell.
Adept Scientific has noted this trend among its UK customers, such as Prosol Electronics, a St Neots-based electronics manufacturer, which recently installed a MiniLab 1008 USB unit manufactured by Measurement Computing.
As Keith Popely, test development engineer at Prosol comments, the new USB unit "has caused a test revolution within Prosol Electronics. It's small size yet large amount of Digital and Analogue IO has enabled Prosol Electronics to automate a number of functional tests at an affordable price. It's easy to program, even for a novice such as myself."
Another advantage with USB is that the bus can power peripherals, so the DAQ system does not require its own power source, so easing system installation and use.
USB devices can also distance sensitive A/D converters and amplifiers from the electrically noisy environment inside a PC housing, which protects the DAQ device in certain applications.
Grant Instruments, a Cambridge,UK-based measurement and control systems company, recently introduced its Datataker DT81 as the world's first data logger with USB flash support. The product was developed to allow the use of low-cost USB memory sticks to unload, control or reprogram multiple loggers.
Nathan Neal, commercial manager for DAQ products at Grant Instruments, links the development to customer demands for features and functionality that meet data collection requirements across industrial, scientific, R&D and environmental applications.
"First and foremost, our customers demand well-engineered, robust, reliable products that are designed to work in the most challenging environments. They also want products that are easy-to-use and configure - and they must be suitable for both the novice and expert user," said Neal.
"Web-enabled features are another high priority for clients as more and more want to access their logger or loggers remotely over a local or wide area network - wireless and Bluetooth access capability is also on the horizon," Neal continued.
As the USB was originally developed to replace low-speed peripheral cabling, many engineers fail to see its potential as a high-performance data-acquisition channel, commented Thorsten Beierle, a senior application engineer at Data Translation Inc. - a US supplier of data acquisition products.
While the original USB specification had only a modest bit rate, high-speed USB 2.0 performs at 480Mbps, fast enough to handle 60MBps data streams, he believes.
The protocol, admitted Beierle, does reserve some bandwidth for interrupts and control transfers, and data packets have overhead bytes. But even with these reductions, the bus can easily sustain more than 10MBps of continual data transfer, he said.
According to Beierle, the proper mode to use for DAQ on USB is bulk transfer. That, he said allows for the resending of corrupted packets, ensuring data accuracy, and allows fairly large 512-byte blocks, keeping overhead effects down.
The drawback is that bulk transfers do not have guaranteed timing. The USB host controller assigns bandwidth for bulk transfers but reserves priority for interrupt and control transfers. So the bandwidth for bulk transfers is an average, not a sustained data rate, Beierle stated.
"The DAQ system therefore needs FIFO buffering to hold data while waiting for the bus to become available and to support the retransmission of data when noise corrupts a transfer packet.
"The software drivers should also allocate buffer space in the host system at the receiving end. This decouples the host system's data-processing activity from the data acquisition so that neither activity can delay or impede the other's performance."
The USB interface hardware and the host controller software have also be found to seriously constrain achievable USB data rates.
For instance, said Beierle, using a USB microcontroller to handle the transfers can result in lower-than-optimal performance because of its software implementation.
According to the Data Translation engineer, a much faster interface can be achieved by using a state-machine hardware controller optimised for 512-byte transfers.
On the host side, traditional Windows drivers can exhibit significant latency as they allocate buffer space in response to an incoming USB transfer. Developers can address this problem by creating drivers that pre-allocate buffer spaces of the right size.
"Our experience shows that we can create USB modules that can sustain reliable data rates as great as 10.9MBps, corresponding to sample rates of 5.45MSps," said Beierle.
Data Translation also see significant potential to take USB-based data acquisition technology to "even higher levels with additional buffering and driver optimisation," concluded Beierle. DAQ is expanding into highly specialised areas thanks to advances with Field Programmable Gate Array (FPGA) technology.
While some in the industry believe FPGA is very much like a PLC, "it is a completely different animal," according to Ian Bell, marketing manager National Instruments UK and Ireland. The main difference, he said, is that FPGA devices can cycle at 40 megaHertz. And as no software is involved once the design has been created, "it can do the things a PLC can do and go beyond that. From a speed perspective we are talking about microseconds terms as opposed to milliseconds," said Bell.
"This next generation capability is proving to be quite a disruptive force in many applications. I don't think everyone in the marketplace appreciates that yet," he added.
FPGA also gives the end users the capability to reconfigure the gates on the FPGA to construct whatever logic he wants. On-going work to develop graphical, higher level, easier-to-use tools means a broader range of scientists and engineers are starting to use the technology, added Bell.
As configuration can be done on systems such as NI's LabView these advanced capabilities are now available to many automation engineers, continued Bell: "Instead of engaging a hardware designer or an electronics engineer to design a board, you now can do it with this graphical software. This is really broadening out the number of people in the automation field who can tackle such difficult jobs."
FPGA is cropping up in areas such as custom triggering applications and high speed control alogarithms for machine protection, where it effectively allows the creation of hardware that is not reliant on software or an operating system.
"Once the FPGA is configured to take account of several input channels and you combine them together to respond to perhaps shut the machine down it is like you have just created a piece of hardware to do that," according to the National Instruments UK marrketing manager.
Bell went on to cite developments in the area of "intelligent data acquisition", which involves putting an FPGA device onto a PC board and surrounding it with a whole set of DAQ channels which it can access.
"With our LabView FPGA module this allows us to configure custom hardware to operate with those data acquisition channels. It's like building a custom board without having to design and manufacture a new PCB."
Among the key enabling technologies behind these trends is USB (Universal Serial Bus) — originally introduced as a low-speed peripheral bus, but now being used increasingly to support high-speed DAQ in a broad range of applications.
Plug-and-play installation of USB peripherals is a particular attraction of this computer interface technology, as it means that DAQ users no longer have to set up and configure the hardware to use it. Also, USB handles data streams in logical channels, called 'pipes', that form a logical connection from a hardware channel to an application, further simplifying setup and ensuring that data automatically travels to the right destination.
"It is so much easier to get the devices up and running, while the cost has come down as well," comments Ian Bell marketing manager, National Instruments UK and Ireland. "Fundamentally, you can deliver the same performance with a USB external pod in terms of accuracy and measurements as you can with a plug-in card." However, he added, when you get up to the limits in terms of speed, then a PCI Express card is always going to be faster.
USB is now commonly used to enable process engineers do some quick data logging so that they can analyse an issue. Engineers, for example, typically plant a laptop down next to a machine, plug in a USB DAQ device and then plug in some sensors, like vibration or temperature sensors.
"In some companies it has become practical for every process engineer or every maintenance engineer who has a laptop to also have one of these little data acquisition pods as part of their toolkit," said Bell. In effect, he added, there is now "a new class of users, which you might class as a more casual data acquisition users, who don't want to have to do programming or want to have programming that is very easy to use."
The evolution of easy-to-use USB DAQ plus off-the-shelf, read-to-run software then it makes it possible for people who are not necessarily engineer qualified, software engineers or programmers to be able to acquire data, continued Bell.
Adept Scientific has noted this trend among its UK customers, such as Prosol Electronics, a St Neots-based electronics manufacturer, which recently installed a MiniLab 1008 USB unit manufactured by Measurement Computing.
As Keith Popely, test development engineer at Prosol comments, the new USB unit "has caused a test revolution within Prosol Electronics. It's small size yet large amount of Digital and Analogue IO has enabled Prosol Electronics to automate a number of functional tests at an affordable price. It's easy to program, even for a novice such as myself."
Another advantage with USB is that the bus can power peripherals, so the DAQ system does not require its own power source, so easing system installation and use.
USB devices can also distance sensitive A/D converters and amplifiers from the electrically noisy environment inside a PC housing, which protects the DAQ device in certain applications.
Grant Instruments, a Cambridge,UK-based measurement and control systems company, recently introduced its Datataker DT81 as the world's first data logger with USB flash support. The product was developed to allow the use of low-cost USB memory sticks to unload, control or reprogram multiple loggers.
Nathan Neal, commercial manager for DAQ products at Grant Instruments, links the development to customer demands for features and functionality that meet data collection requirements across industrial, scientific, R&D and environmental applications.
"First and foremost, our customers demand well-engineered, robust, reliable products that are designed to work in the most challenging environments. They also want products that are easy-to-use and configure - and they must be suitable for both the novice and expert user," said Neal.
"Web-enabled features are another high priority for clients as more and more want to access their logger or loggers remotely over a local or wide area network - wireless and Bluetooth access capability is also on the horizon," Neal continued.
As the USB was originally developed to replace low-speed peripheral cabling, many engineers fail to see its potential as a high-performance data-acquisition channel, commented Thorsten Beierle, a senior application engineer at Data Translation Inc. - a US supplier of data acquisition products.
While the original USB specification had only a modest bit rate, high-speed USB 2.0 performs at 480Mbps, fast enough to handle 60MBps data streams, he believes.
The protocol, admitted Beierle, does reserve some bandwidth for interrupts and control transfers, and data packets have overhead bytes. But even with these reductions, the bus can easily sustain more than 10MBps of continual data transfer, he said.
According to Beierle, the proper mode to use for DAQ on USB is bulk transfer. That, he said allows for the resending of corrupted packets, ensuring data accuracy, and allows fairly large 512-byte blocks, keeping overhead effects down.
The drawback is that bulk transfers do not have guaranteed timing. The USB host controller assigns bandwidth for bulk transfers but reserves priority for interrupt and control transfers. So the bandwidth for bulk transfers is an average, not a sustained data rate, Beierle stated.
"The DAQ system therefore needs FIFO buffering to hold data while waiting for the bus to become available and to support the retransmission of data when noise corrupts a transfer packet.
"The software drivers should also allocate buffer space in the host system at the receiving end. This decouples the host system's data-processing activity from the data acquisition so that neither activity can delay or impede the other's performance."
The USB interface hardware and the host controller software have also be found to seriously constrain achievable USB data rates.
For instance, said Beierle, using a USB microcontroller to handle the transfers can result in lower-than-optimal performance because of its software implementation.
According to the Data Translation engineer, a much faster interface can be achieved by using a state-machine hardware controller optimised for 512-byte transfers.
On the host side, traditional Windows drivers can exhibit significant latency as they allocate buffer space in response to an incoming USB transfer. Developers can address this problem by creating drivers that pre-allocate buffer spaces of the right size.
"Our experience shows that we can create USB modules that can sustain reliable data rates as great as 10.9MBps, corresponding to sample rates of 5.45MSps," said Beierle.
Data Translation also see significant potential to take USB-based data acquisition technology to "even higher levels with additional buffering and driver optimisation," concluded Beierle. DAQ is expanding into highly specialised areas thanks to advances with Field Programmable Gate Array (FPGA) technology.
While some in the industry believe FPGA is very much like a PLC, "it is a completely different animal," according to Ian Bell, marketing manager National Instruments UK and Ireland. The main difference, he said, is that FPGA devices can cycle at 40 megaHertz. And as no software is involved once the design has been created, "it can do the things a PLC can do and go beyond that. From a speed perspective we are talking about microseconds terms as opposed to milliseconds," said Bell.
"This next generation capability is proving to be quite a disruptive force in many applications. I don't think everyone in the marketplace appreciates that yet," he added.
FPGA also gives the end users the capability to reconfigure the gates on the FPGA to construct whatever logic he wants. On-going work to develop graphical, higher level, easier-to-use tools means a broader range of scientists and engineers are starting to use the technology, added Bell.
As configuration can be done on systems such as NI's LabView these advanced capabilities are now available to many automation engineers, continued Bell: "Instead of engaging a hardware designer or an electronics engineer to design a board, you now can do it with this graphical software. This is really broadening out the number of people in the automation field who can tackle such difficult jobs."
FPGA is cropping up in areas such as custom triggering applications and high speed control alogarithms for machine protection, where it effectively allows the creation of hardware that is not reliant on software or an operating system.
"Once the FPGA is configured to take account of several input channels and you combine them together to respond to perhaps shut the machine down it is like you have just created a piece of hardware to do that," according to the National Instruments UK marrketing manager.
Bell went on to cite developments in the area of "intelligent data acquisition", which involves putting an FPGA device onto a PC board and surrounding it with a whole set of DAQ channels which it can access.
"With our LabView FPGA module this allows us to configure custom hardware to operate with those data acquisition channels. It's like building a custom board without having to design and manufacture a new PCB."
