1. Providing a power signal
Modern drive concepts with large combustion engines require precise and fast response of the engine's control systems (e.g. for fuel supply) to respond to abruuptly varying loads. Here, it is essential to ensure that sufficient power is supplied at any time and that, at the same time, the engine features low fuel consumption and safe operating parameters. This requires that a power signal is provided which - with vehicles, compressor and pump systems - needs to be generated using special measuring devices. In general, there are three different approaches:
The following article compares direct power measurement with indirect power measurement on and in the drive train respectively (approaches b. and c.) with regard to the uncertainties of measurement that can be achieved.
All the parameters to be taken into account for (8) and examples A and B are subject to tolerances. They can be assessed as follows:
Example A requires the strain guage positioning tolerances s as well as the temperature error resulting from lacking or limited thermal compensation to be considered in addition. The values of these tolerances are determined by the quality of the strain gauge installation and will therefore not be take into consideration here.
Without further error analysis, table 1 shows that the total error of the measuring devices described above (approach b) is primarily determines by the tolerance of E and μ. It can thus not be less that 3 %, however, in practice, it is often substantially higher.