Engine Testing

Introduction

The NP4000 instrumentation is used to monitor engine noise characteristics. The high sensitivity of the device has enabled the tappet noise and cylinder knocking problems to be identified and classified from normal background operations. Customized proprietary software has been developed to identify engine noise characteristics and report details directly to the operator. The Network operation of the instrumentation has enabled large numbers of test bays to be operated from and analysed by a single PC. Information from the test bays can be directed to production as well as quality control engineers for simultaneous analysis. Analysis of the data can be carried out independently by each engineer using the system. Results can be passed to remote readout units and directly into third party application packages.

The following pages are application notes for engine testing using accelerometers for determining tappet settings.

Sensor selection

ICP Accelerometers were used to monitor the engine vibrations caused by the opening and closing of tappets. The sensors had to have a wide enough dynamic range so as not to be overloaded by engine firing, yet sensitive enough to be able to pick out tappet movement. In addition a tachometer output was used to determine the overall speed of the engine.

Data Acquisition

A NP4000 series data acquisition unit was used with high speed 78KHz data acquisition cards installed. The cards contained all the signal processing electronics for direct connection to the accelerometers including digital filtering, and ICP excitation currents.

Post processing and analysis

A combination of signal processing algorithms, neural network analysis, and statistical analysis techniques were used to analyse the data and determine the tappet settings. This was linked to a user interface screen to display the tappets for each of the cylinders, and give a pass or fail notification.