Measuring vibrations on engine manifolds

The optimisation of internal combustion engine operation is becoming increasingly important. For engine management purposes, a whole series of measurements need to be carried out. The temperature of the exhaust gas is one important parameter and is measured using a thermocouple mounted within the engine manifold.

To verify the way it is mounted, it is necessary to examine the propensity to vibrate, as well as the mechanical rigidity of the structure. This is an application where the blue laser sensor offers specific benefits. Due to the high temperatures in the exhaust gas flow, the thermocouple becomes red-hot or self-fluorescing.

With red-hot, glowing objects, a conventional red laser has a high signal interference from the surface of the brake disc, because it emits the same or very near wavelengths of light as the red laser. However, the blue laser works at a wavelength of 405nm, which is far from the red part of the visible spectrum. This means it is easier to filter this type of emitted light from the brake disc, which ensures very stable signals.

A narrow slit provides sufficient free space for the optics. The high ambient temperatures are effectively reduced for test operation by using a protective plate, whilst a blower ensures clean optical conditions and cooling.

Due to the sensor‘s high speed sampling frequency (2.5kHz), the expected vibrations can be accurately measured and then easily evaluated via digital interface to a PC.

Demands on the measuring system:
- Measuring range 20mm
- Accuracy to 20μm
- Measurement on red-hot objects

For more information on Micro-Epsilon’s range of laser displacement sensors, please call the sales department on 0151 355 6070 or email: info@micro-epsilon.co.uk