What about electrical power? Firstly, it is generally true that it is difficult to measure electrical power consumption directly. In addition, the standard specifications of DIN IEC 60034-2-3 require high measurement accuracy.
We therefore have two measured variables (current and voltage) whose errors add up according to the law of error propagation in the multiplicative calculation of the power (U*I).
Both variables individually (current and voltage considered separately) are a concatenation of at least four errors:
Amplitude error (across all frequencies)
Phase error during sampling (across all frequencies)
Bandwidth limitation of the number of harmonics (at least 29 harmonics for 0.1.% accuracy of voltage or current)
Error of the supply lines and any current transformers used
The sum of these 4 errors determines the resolution of the two measured variables (voltage and current). We therefore have a total of 8 sources of error, the sum of which must not exceed 0.3%. As mentioned above (reference to the standard, point 7.2), one should even be a little better.
So on average, each error source may only contribute roughly 0.03% error.
This means that a square wave signal must be cleanly recorded at 53 harmonics with a synchronicity of better than 3ns.
When operating an electric motor, the quasi-sinusoidal signals generated by the PWM control must be able to reproduce very different motor speeds and therefore sine frequencies and amplitudes. It should be noted that not only the required sine frequency but also the sine amplitude increases with increasing speed.
So if you want to cover a speed range from 1% to 100% of the motor, the amplitude in the slow speed range is only 1% of the amplitude at full speed.
The measuring range end value must therefore not only be resolved to 1/0.03% = 3333 steps, but to 333333, which corresponds to an effective resolution of an AD converter of 18.3 bits. And that is after deducting all noise and distortion of this AD converter.
This results in the high demands on the measuring devices, which the LTTsmart Power Analyser fulfils.
With its 24-bit AD converter and 4MHz sampling rate, it fulfils the power measurement requirements of a PWM-operated electric motor. Its channel synchronisation is better than 1ns and its galvanic isolation of the channels offers not only safety, but also a very low stray capacitance in relation to the housing mass.
If just one of these requirements (sampling rate, resolution, synchronisation, galvanic isolation with low stray capacitance) is not implemented perfectly, the efficiency measurement fails in accordance with the DIN IEC 60034-2-3 standard.
All these points are carefully harmonised in the LTTsmart measuring system from Labortechnik Tasler GmbH. The measurement technology specialist has been established on the market for over 25 years and was already active in high-resolution megahertz ranges when the measurement technology market was slowly switching from DOS to Windows.
The requirements of e-mobility are now driving the market from two directions into this niche of broadband precision measuring devices:
slow PC measurement technology lacks bandwidth and fast oscilloscopes lack amplitude resolution.
To determine efficiency, (slow) mechanical performance data must also be recorded.
Of course, this can also be covered by the LTTsmart in a highly synchronised manner.
In many cases, however, it makes sense to use additional measuring devices from Gantner Instruments, which work seamlessly with the LTTsmart, to record the large amount of (slow) additional information, such as temperatures.
The user benefits from the fact that the LTTsmart is perfectly adapted to the demanding measurement task of electrical power measurement and works seamlessly with other measuring devices.
The comprehensive functionality of the power analyser is available both in the cross-industry LTTpro software solution and in Gantner's GI.bench and connects all frequency worlds with each other in a highly synchronised manner. Slow, medium-fast and very fast measurement signals are combined online into the required analysis variables.
The large amounts of data required for the calculation of the electrical performance indicators described above remain unnoticed by the user in the background. At the same time, however, the user or a software-adjustable decision criterion can record entire sections of this fast raw data and analyse them at any time in order to discuss any anomalies in the recorded parameters.
Whether for research purposes or for process and quality monitoring: as a user, you always have full access to all signal worlds. From the overview to the finest detail.
This makes the Power Analyser solution (among many other solutions) from LTT the perfect - and even unique - complete package, thanks to which you can also keep pace with the rapid development of electromobility.
