Simultaneous measurement of two peaks proved tricky for engineers measuring oil viscosity, until a novel solution using Tektronix's TDS3000 digital phosphor oscilloscope was presented
At Kittiwake, the Littlehampton-based designer and manufacturer of test equipment for marine and offshore oil applications, Tektronix was able to provide an application-specific solution for a demanding research project.
Kittiwake was established in 1992 by Chris Leigh-Jones and Steve Weston to design and manufacture fuel and lubrication test equipment.
The company's equipment is used in more than half of the world's ships, and it supplies oil companies such as ExxonMobil, Shell and Texaco with oil analysis programmes for ships engines and test equipment for field testing of fuel and lubricant oils as well as test equipment for water treatment. Kittiwake's development engineer, Michael Dines, was investigating new ways to measure viscosity when he came up against a 'brick wall'.
The analysis is based on simultaneous measurements of two events and two peak-to-peak measurements (also simultaneous), and it was this that was proving a real problem.
It was, as Dines says, proving to be "'an absolute nightmare", as generally a scope can average peak accuracy but, while measuring the peak of one graph, the other peak changes.
He needed to look at two peak measurements simultaneously to calculate viscosity.
Dines was already using the two-channel, 100MHz bandwidth, 1.25GS/s sample rate per channel TDS3012 digital phosphor oscilloscope (DPO). This scope is part of the Tektronix TDS3000 series, which allows for video content of signals to be displayed, just like an analogue oscilloscope, for use in troubleshooting and adjusting video systems.
The series includes a video module which provides line-count triggers to capture particular video signals.
In this case, the TDS3012 offers 20MHz bandwidth and a time base of 4ns to 10 seconds per division with a 200ppm accuracy.
This model is one of six models in the series, which offers either two or four channel options and with sample rates per channel of up to 5Gs/s. Each DPO has an intensity-graded colour display to provide information about the signal amplitudes, frequency and widths. With sample rates of up to 1.25GS/s, the fast update rate makes capture and display of infrequent waveform or their variations easier.
However, this particular research required simultaneous readings of simultaneous measurements.
It was found that, by connecting the TDS3012 DPO to the Kittiwake network, via the TDS 3DM ethernet interface box, the readings can be viewed anywhere in Kittiwake's research and development section.
Although this helped with taking and recording readings, it did not solve the problem of the simultaneous data logging of the measurements. A breakthrough came when Dines was discussing the project with a representative from Tektronix distributor TTi (Thurlby Thandar Instruments).
He suggested using the Tektronix Wavestar software with the Tektronix DPO.
With this, Dines was able to view the graphs on his PC and to use the software to simultaneously set up and data log all measurements, such as amplitude, peak-to-peak, cycle, mean, as well as current, maximum, minimum, average and standard deviation.
The TDS3012, as with all DPOs in the series, has a 10K points record length, offering flexibility and versatility in storage and analysis of signals.
With this combination of the TDS3012 and Wavestar 2.4, the two peak heights could be looked at simultaneously, while Wavestar software's Strip Chart facility enabled them to be plotted.
In this way, they could be measured and plotted against each other for a view of what was happening at any given time.
There is an average of two peak heights over the same period, with displays to an extra four decimal places with the Wavestar software-enabled version, compared to the three decimal places provided by the scope.
Where precision and accuracy are crucial, this measurement facility opened up Dines's research possibilities.
He summed up the combination in this way: "I wouldn't be able to do the project without this scope and this software." This fusion of hardware and software meant that the vertical resolution of the TDS3012 could be used to its full potential.
It is, says Dines, the vertical resolution of 9 bits that distinguishes this scope from others available and which provides the clarity of resolution that is required for the peak comparisons in his research.
With Wavestar, the waveform can be dragged into Microsoft Excel and looked at in that environment before taking measurements.
Dines described Wavestar 2.4 as "incredibly intuitive" - it took him half an hour to work out how to use the scope to get the measurements required.
Wavestar's 'drag and drop' system operates with Microsoft Word, and so diagrams can be dropped into documents - for reports, for example.
The system can also plot into Microsoft Excel, which Dines uses for plotting into reports.
As the TDS3012 plots every second, the mass functions can be set in Excel for presentations or transfer of data.
The Strip Chart facility enables two heights to be presented simultaneously and changed with temperature and vibration.
The Data Logging facility enables standard deviations to be derived for two peak heights, current, maximum and minimum to give an indication of the stability of the device under test. This means that overnight analysis can identify drift and other behaviour.
The waveform can be put on the Notes sheet, and notes can be made for further research.
Dines used this to send examples of his tests to Tektronix to establish what kind of equipment would be required; it can also be used to record and illustrate or discuss any operating queries.
With the Waveform Tabulator, individual points on a waveform can be viewed, with each value being listed.
This information can be plotted on to Strip Charts, and then viewed at individual points.
The joy of the assembly for Dines is: "Any data that you can see can be plotted." This has proved especially useful at this development stage, as it means that how any changes can occur with changes in conditions can be viewed.
The solution also addressed the 5 metre limit set by the use of an RS232 cable. With the scope running over the network, it can be positioned anywhere in the office and, when linked to the PC, readings can be taken from a distance.
This means that heat-sensitive tests need not be monitored by the scope user positioned near the department's assembly oven, where temperatures can range from -40 to +120C, for example, but can be analysed from a more comfortable distance.
The TDS3012 saves valuable time in the R and D department of Kittiwake.
Just as documents can be saved on the PC, the scope set-up can be remembered and reinstated.
In addition, the limit of eight function savings on the scope can be negated when the research project is an intensive and long-term one, as here.
The fact that an engineer may want to return to a set-up that was used a year ago can prove problematic, in that recapturing the exact configuration is critical to precision research.
However, as Kittiwake discovered, with the PC option, the setting can be stored for long-term future use.
The function also means that the fact that the scope is shared among the company's R and D staff does not mean that all its setting-saving options are exhausted by one particularly intense project.
The TDS3012's QuickMenu User Interface Mode allows quick and easy operation.
This quick access user interface enables the main controls of the scope to be accessed via a single button.
The simplified and streamlined front panel means that the scope can be used effectively with a shallow learning curve.
Dines, an engineer, had never used an oscilloscope before in his life, yet found the logical programming enabled him to set up the scope and the software to be operational in minutes.
By the same token, timing of the channel can be changed in seconds, says Dines, for conditions to be the same as the last set of measurements.
Previously, says Dines, it could take up to five minutes to change settings and channels.
Now, with the Waveform 2.4 incorporation, the last worksheet used can be loaded and displayed on the PC screen and, at the same time, the settings can be loaded to the TDS3012, ready for use.
This means that his intensive research does not use up all the DPO's time and settings, making it available for other team members to use.
The storage application of the scope is also vital for Dines's project, in which collecting data is the key.
With the portable TDS3012/Wavestar 2.4 configuration, it can be linked by the network across the factory and from the desk.
The scope was used to tune and find problems, using the DPO as a data logger, with the increased capabilities it offers providing peak and frequency of peaks and accuracy that a standard data logger could not provide at a realistic cost, says Dines.
The portable scope is compact and lightweight, weighing 3.3kg, and can be battery-operated, enabling a series of specially designed tests in different locations to be created.
In addition to the RS-232 module, the TDS3000 series also offers GPIB and VGA communications ports as optional modules.
