Working closely with HBM’s team in the UK, Mahle Powertrain used their piston telemetry system, comprising a mechanical linkage mechanism from the conrod big end, to route signal wires enabling the acquisition of real-time piston data from a fired engine. By fitting eight thermistors at specific points just below the surface of the piston’s combustion bowl and ring lands it was possible to derive the actual temperature measurements within the piston when the engine was running. Because of the temperatures in the pistons, glasscoated silicon chip thermistors were used of the negative temperature coefficient variety.
"The challenge with these thermistors is that they produce a nonlinear output. However, HBM’s catman® software is more than capable of dealing with this aspect."
Carl Godden, senior instrumentation engineer, Mahle Powertrain
This set-up produced a twelve-point calibration curve for each sensor at temperatures of up to 350°C. The curves were incorporated into catman® as user scaling files (USC). catman® was configured to perform linear interpolation between the calibration points.
To provide a complete picture for Mahle Powertrain, HBM had a number of other inputs into the MGCplus. The oil feed temperature and flow, which is controlled automatically using a heater and valve, were also monitored along with other basic engine parameters such as the torque and speed. The measured data was simply and clearly displayed using catman® real-time graphical tools.
Carl Godden, senior instrumentation engineer at Mahle Powertrain recommends the solution:
"The MGCplus and catman® combination proved to be an excellent solution for our data acquisition requirements. It was particularly rewarding to obtain a multi-point linearization of the thermistor signals that was very simple, and highly effective, to implement."