Time to clear away the clutter

27 May, 2006

(27/05/06) The Cleverscope Model CS328 offers high EMI immunity and the ability to cut and paste images to a PC, features that are proving useful in the development of spark ignition projects writes Neil Reynolds, Test & Measurement Instruments product manager, Aspen Electronics…


In an ideal world, electronics engineers want instant access to a wide range of tools, all of which are accurate, reliable, easily reconfigured and interconnected, and of course, don't clutter up the workspace. The Cleverscope Model CS328, a USB-connected, PC-hosted oscilloscope and spectrum analyser combined looks set to make this happen. Available in the UK from Aspen
Electronics, the Cleverscope is said to be easy to use, is based on Windows, and integrates with standard Office packages.

Graphs and data can be copied and pasted to other applications, saved or loaded from disk, and printed. Key hardware features include: two 10 bit analogue channels, sampling simultaneously at 100Msamples/sec; external trigger; eight digital inputs sampling at 100Msamples/sec; and 4Msamples of storage.

Software facilities include: spectrum analysis; signal averaging and filtering; extensive mathematical functions; and signal measurement, including peak, RMS, DC, pulse width, period and frequency. A 0-10MHz signal generator option is also available.

The Cleverscope is already proving extremely useful in design and development applications. Roger Marmion, an electrical and electronics systems engineer, formerly with Cosworth Racing, is particularly impressed. He is using the Cleverscope to capture waveforms for two spark ignition projects. One is very high energy for land-based gas turbine applications, and the other is for historic racing car applications.

“I like the fact that the 'scope weighs practically nothing, and takes up very little bench space. The software is good, and straightforward to use,” he said. “The ability to cut 'n' paste screenshots, and to annotate and scale in appropriate units on the axes are particularly useful features,” he added.

According to Marmion, now running his own Engineering Design Company, the trigger set up is excellent, and he was pleased to be able to capture a component failure. Figure 1 shows the gate driver output of a PWM controller at the moment of failure (blue trace), as the output stage is damaged by the ignition discharge. The fault was caused by an error in the PCB layout, causing an inductive PCB ground connection. The red trace shows the spark plug current.

“Note the very high amplitude spikes as the capacitance of the spark plug discharges through the spark gap, followed by a damped sinusoidal current due to the energy storage capacitor and ignition coil inductance resonance,” Marmion explained. “Knowing I only had one shot at it, this was an impressive result from the Cleverscope,” he added.

However, Marmion maintains that probably the most notable feature of the Cleverscope is the maths capability. “I am able to display spark energy directly from the spark voltage and current,” he said.

The image above shows how the maths function is used to establish the energy delivered by a different type of ignition system to the load. “The red trace shows the effect of multiplying the spark current by the load voltage, then integrating.” Note that the axis has been re-labelled directly in Joules.

“Importantly, the Cleverscope determined that the total energy delivered is 2.644J, typically 25 times that delivered in a normal car ignition discharge!” said Marmion. Measuring these voltages and currents requires some special test arrangements. For example, very short scope probe ground connections are required, which is achieved by winding tinned copper wire around the ground sleeve of the scope probe tip, and soldering this directly to ground as close to the measurement point as possible. Current is measured using 0.01Ohm surface mount current sense resistors with very small inductance.

“Needless to say, this work generates significant electrical interference”, Marmion commented. He recommends connections be as short as possible, and any current carrying wires are co-located (preferably twisted) with their associated current return wire to minimise the area of the current loop and hence radiation. Failure to do this can result in disruption of, or damage to, nearby equipment containing microcontrollers or processors, he warned.

“I am impressed by the EMI immunity of the unit, despite the fact that the high energy discharges causes havoc for electrical equipment in the vicinity.”

In conclusion, Marmion highlighted several significant Cleverscope facilities: the ability to do complete timing and amplitude analysis using cursors; the maths functions used to calculate instantaneous power and energy traces; and the ability to re-scale and label the vertical axis to show Joules. Also noteworthy is the robustness of the hardware when used to make measurements in environments with high levels of electrical interference or on circuits causing lots of interference.

Aspen Electronics
For more information, visit www.aspen-electronics.com

T: 020 8868 1311