By Jim Montague, Executive Editor
Recorders and data acquisition (DAQ) systems are dead! Long live recorders and DAQs!
Technical advances in process control and automation often unfold in unexpected and ironic ways. Software fuels a renaissance in supporting hardware. Wireless needs more cables at the transmitting and receiving ends. PCs increase paper and printing instead of replacing it. You get the idea.
Not surprisingly, DAQs and other data loggers are no exception. These devices were supposed to be overtaken and replaced by any computer with a software-based historian, data collection interface, and reporting and trending functions. There’s no doubt this is happening to some extent. Low-cost computers in all their various forms are taking on data-recording jobs in traditional settings and in locations where recording used to be too costly or inaccessible.
However, while recorders’ and DAQs’ days may seem to be numbered, computer- and software-based logging seem to have merely whetted users’ appetites for data recording, archiving and analysis. Also, many industrial settings remain where computers can’t perform as well as traditional DAQs. So, who gets the call when this happens? You guessed it.
“Users who never had recorders or historians before are adding them now because software allows it. A lot more companies are gathering more information in more applications to help make business decisions,” says Steve Goldberg, industrial systems division director for Matrix Technologies, a CSIA-registered system integrator in Maumee, Ohio. “For example, we work with a steel mill that processes coils, and it’s now able to record, archive and trend fast, millisecond-level data that it couldn’t acquire before to check for quality.”
Ashish Desai, sales engineering supervisor at Omega Engineering Inc., adds that, “Many non-technical people are beginning to use DAQ products, and they have differing levels of expertise. So it’s even more important for us to help them define their expectations for recording and teach them how to use loggers and DAQ systems that will work best for them. For example, we even had one user put 26 inexpensive loggers in a shipment of refurbished PCs being trucked from the East Coast to the West Coast. They previously had problems with equipment suffering heat damage during shipment, and so the loggers helped them monitor temperatures in the truck.”
Similarly, making sure that newly drilled oil and gas wells have been properly sealed usually requires trucking a mobile DAQ system between wells to check and document the status of each. After a well is drilled, a steel casing is lowered into it, and cement is pumped in to create a seal between the casing and the rock. Of course, this job means lots of heavy vibration and dust that can play havoc with typical PC-based data collection equipment.
To avoid this problem, one oil and gas logging and perforating company has built a ruggedized DAQ system to do its electronic well surveys, which consist of logging cement quality, gamma radiation, temperature and depth. Rocky Mountain Wireline Service in Grand Junction, Colo., reports it reduced downtime and increased accuracy of its surveys with its home-grown DAQ system that uses National Instruments’ LabWindows/CVI software and PXI/Compact PCI hardware.
“Our traditional DAQ system is rack-mounted in a wireline truck. It must withstand vibration and dust as the truck travels over rough roads, which causes problems for industrial PCs. For example, the RAM chips and A/D cards often vibrate out of position, even with retainer bars and clips holding them in place. These PC maintenance requirements and resulting truck downtimes were a problem. We needed a new system that was reliable and easy to repair or replace,” says Corin Chepko, Rocky Mountain’s owner.
The company’s DAQ system records acoustic cement-bond logs, which determine the quality of the cement between the well casing and surrounding rock. An acoustic bond tool emits a 22-kHz ‘tick’ 20 times per second and measures reflected arrivals of sound for 1,000 microseconds. The acoustic tool is stacked with a gamma ray tool, which emits a pulse when it detects a gamma ray, and a casing collar locater tool that adds a low-frequency component. The signal that comes up from the single conductor wireline is separated into two signals before it enters the A/D boards—one with the low-frequency component of about 10 Hz removed, so the analog trigger pulse remains on a flat baseline, and the other with the low frequency intact. A digital input from an optical encoder calculates the tool depth. When the acoustic tool ticks, a -5 V trigger pulse is sent up the line to indicate the arrival of the sonic signal. Upon detecting the acoustic trigger, the system scans the analog channels at 256 kHz each for just under 0.05 sec (11,800 samples), then transfers the data for processing and rearms the trigger to be ready for the next acoustic trigger.
“We decided to use PXI hardware for our latest upgrade because of its ruggedness and modularity. We’re planning to expand the system’s capabilities in the future, so we chose the PXI-1050 chassis because it has eight PXI slots to accommodate our application, as well as four SCXI slots for signal conditioning if we add more inputs, such as line tension,” adds Chepko. “In the end, upgrading our software for the PXI system was quick and easy, and we can achieve better logging performance with PXI hardware. Upgrading to a PXI DAQ system resulted in valuable time savings, as well as plenty of room to upgrade future system functions. Using LabWindows/CVI made the software transition fast and easy. The new system reduces truck downtimes and computer maintenance, and technicians don’t need to solve problems immediately in the oil field because modules can simply be replaced and fixed at a later time. With the increased accuracy of our hardware, we can deliver a higher-quality cement bond log to our customers and a quicker depth determination with our casing collar logging program.”