Carrying out the measurement
Due to the increasing number of electrical and electronic consumers in vehicles, there is a demand to reduce CO2 emissions and consumption by increasing the efficiency of electrical and electronic systems. In order to achieve this goal in the long term, currents, voltages and temperatures at power-intensive vehicle components such as electric heaters, pumps and headlamps must be measured and validated. In vehicles with a 48V board net, relevant components include the DC/DC converter, the electrical machine or the 48V battery itself, since extremely high-power levels occur here for a short time. Some examples of measurements on power-intensive components are explained below.
During recuperation, when braking the vehicle, energy is recovered and not converted into heat by being fed back into the battery. However, voltages and currents or powers must also be measured and validated for the above- mentioned components during the development and test phases. With the new measuring modules, calculated values for current and voltage measurements, such as the charge, discharge and total balance, power and work can also be calculated online during the measurement and output on the desired interface. On the one hand it is necessary to detect fault currents or currents that are too high at an early stage, on the other hand it is a great challenge to implement this. High-resolution measurement technology for extremely wide current, voltage and temperature ranges help test and development engineers to successfully meet this challenge.
For energy and battery management, voltages and currents of the entire system and of individual consumers must be measured. Due to the joint measurement of current and voltage with a single I/U-combi probe, only one measuring input is required in conjunction with the MULTI-4/MULTI-8, since two synchronously sampling AD converters are available per measuring input. The current is measured via a low impedance measuring shunt, the voltage via a voltage divider. The unique Auto-Range function allows the measurement of quiescent and operating currents and voltages with the best possible resolution. The measuring range does not have to be pre-selected during the set-up of the measuring technology, which considerably reduces set-up times. In the table below are the measuring ranges, resolutions of the AD converters as well as of a 1 mΩ and 200 µΩ HI/U combination sample:
The maximum continuous current of the 1 mΩ sample is 120 A at the maximum achievable resolution of 300 µA/bit in gain 100, while the resolution under full load is 7 mA/bit.
The calibration values of the shunt and the voltage divider are stored in the Probe and are automatically read out when the Probe is connected to the measuring module and calculated in the measured value processing. The calibration value of the shunt is the real resistance value measured on the test bench. The output interface of the measurement data is freely configurable. Two CAN interfaces and a 100 Mbit/s Ethernet interface with XCP-on-
Ethernet or the KlaricServer are available for this purpose. The DBC or A2L file is automatically generated with a mouse click in the KlariToolBox with all connected Probes. The "plug and measure" principle considerably reduces the set-up time. All necessary values are calculated and output during the measurement by the online calculation of the power, charge, discharge and total balance. This allows a particularly simple evaluation without having to carry out countless additional calculations afterwards.
Evaluation of the measurement
The following illustration shows the starting process of a conventional 6-cylinder diesel vehicle with 12Von-board power supply, which was recorded with a KLARI-CORD 4 during a long-term measurement. The measured peak current during starting is -757A with the on-board voltage dropping to 8.7V. These values also depend on the selected sampling rate. Since the conventional 12V electrical system has seen a rapid increase in power and thus also in currents, more and more models with 48V electrical systems will be available in the future.
U_min = 8,7V I_max = -757A
A closer look reveals that the sampling rate is not constant, but dynamic. In all new measuring modules, a threshold for current, voltage or temperature can be set at which the sampling rate is changed. This leads to the fact that, for example, quiescent current measurements are sampled with only one Hertz. If the measured value now rises above the set threshold, the peak current and the signal form can be evaluated and conclusions drawn about the cause. When measuring the current and voltage of the electromechanical steering system, the dynamic sampling rate helps to considerably reduce the data volume to be evaluated, since, for example, permanent recording can be made during measurement runs without switching the measurement technology on or off. This applies in principle to all measurement tasks, including the DC/DC converter, where the currents are almost static.