Products Used:
LabVIEW 7.1

The Challenge:
Replace a standalone hardware interface with a new PC-based system including a Graphical User Interface GUI to  provide automatic control of an Oil Viscosity Sensor with a data logging facility to increase efficiency of the characterisation process and verify methods of autotuning the system.

The Solution:
A PC-based solution was created using LabVIEW. The data samples used for viscosity measurement could  therefore be visualised, as well as the interpretation algorithms to be implemented. The interface also allowed the operating frequency to be monitored across a range while logging the output.

Background to the device and the problem
Replacing engine oil when it is has deteriorated, instead of on a time or distance basis, can help protect the engine as well as reducing the financial and environmental cost of replacing the oil unnecessarily early.

A sensor has been developed that determines viscosity of the oil by measuring the amount of shear-wave energy  that the oil

absorbs. Determining the optimum operating frequencyof the device is part of the characterisation and tuning process for the sensor, which had hitherto been carried out using a laborious manual process. For each individual sensor in a batch of samples, the process involves recording the output over a range of frequencies at different temperatures. This has to be repeated for different oils.

As the sensors undergo an initial settling process with heating, the process must be repeated to verify that they  are still performing correctly.

Method of operation
The viscosity sensor itself consists of a stepped metal rod with a piezo-ceramic shear transducer at one end, the other end sitting in the oil. Only a proportion of the waves can enter the oil by virtue of an impedance matching layer. (See Figure 1). The transducer is excited at a set frequency, sending a pulse of shear waves through the rod. These waves travel to the other end of the rod where they are either (i) coupled into the oil via the
measurement surface and absorbed, (ii) reflected by the measurement surface or (iii) reflected by the reference surface. Once the pulse is sent, the piezoelectric element is used as a