A Battery Test System is used to test and optimise electrochemical energy storage devices such as batteries. Battery Test Systems make it possible to document the change in the block voltage of batteries over the entire course of capacity tests. Behind these changes in the block voltage is a natural phenomenon that can be observed in particular at the beginning (so-called voltage sag) and at the end of the discharge process of batteries. In addition, a Battery Test System can also read out further data that provide comprehensive information about the condition and function of the battery. These are charge and discharge current, temperature, cell voltage and total battery voltage.
Software for controlling and logging measured values from Battery Test Systems
A multitude of interfaces allows the evaluation and logging of the measurement series of a Battery Test System in a computer-based application. In order to give the user maximum control over his Battery Test System, such software solutions are used on the one hand for the graphically and tabularly prepared monitoring of the measurement data and inform the user on the other hand about mean values, minimum and maximum values of the voltage measurement. On the other hand, the software is also designed to facilitate the selection of the measurement data relevant for the respective test purposes, so that it ultimately also plays a central role in the control of complex battery test systems.
A Breakout Box is an electronic measuring instrument for monitoring and rerouting the signal transmission between at least two devices. As intermediate switching devices, breakout boxes are simply connected directly between the cable connection and the device.
The advantage of a breakout box is, among other things, the ability to integrate non-standard devices into a standard environment. Furthermore, breakout boxes enable communication between data terminal equipment (DTE) or data transmission equipment (DCE).
A cell voltage monitor is a device for real time monitoring of the cell voltage of lithium-ion batteries, fuel cells, electrolyzers and other energy storages. Relevant measured data are especially aging, stack-inhomogeneity and water content of fuel cells. Dependent on the applied cell voltage monitor the cell temperature can also be determined, which is practical particularly for fuel cell monitoring. By means of its multi-channel construction the cell voltage monitor can control up to several thousands of cell units simultaneously.
Cell voltage monitors are either connected directly with fuel cells or integrated in an existing test system. The compact and tough design of a cell voltage monitor makes it perfectly work during in-field use.
Connectivity of a cell voltage monitor
The data of cell voltage analysis, which the cell voltage monitor captures, are either processed directly by the integrated control unit and displayed in real time or transmitted to a computer system by CAN-Bus, LabView or USB connection. Processing and digitalization of measured data in real time has the advantage that disturbances thereby are reduced to a minimum. On the other hand, the transmission of data to a computer system and the application of CVM-software can accelerate the process of data analysis and help to easily manage the configuration of the cell voltage monitor.
CVM, or cell voltage monitoring, is a real-time data acquisition system that can be used to test and monitor the cell voltage of Li-ion batteries, fuel cells, electrolysers and other energy storage devices. Relevant measurement data for the CVM include, in particular, ageing, stack inhomogeneity and the water content of fuel cell systems. Depending on the measuring module used, the CVM also allows statements to be made about the cell temperature, which is particularly recommended when monitoring fuel cells.
Measuring instrument technology for CVM
The measuring devices used in the CVM can either process the cell voltage analysis data directly via the integrated controller and display it in real time or transmit it to a computer via CAN bus, LabView or USB. Processing and digitising the measurement data in real time has the advantage of considerably reducing interference. Thanks to the multi-channel design of the CVM modules, Cell Voltage Monitoring can monitor up to several thousand cell units simultaneously.
CVM software is designed to facilitate the process of data processing and analysis of Cell Voltage Monitoring Systems (CVMS). In this way, the CVM software helps to save considerable time and costs. The CVM is a real-time data acquisition system used to check the cell voltage of fuel cells, Li-ion batteries and electrolysers in real time. After the CVM measurement modules have connected to a computer system via CAN bus, LabView or USB, further processing of the measurement data can begin with CVM software. The measurement data has already been digitally prepared and pre-processed by a CVM measurement controller.
Functional scope of CVM software
The CVM software stores this data and presents it clearly in tables and diagrams. The user interface of CVM Software is intuitive and requires no programming knowledge. Several monitoring projects can be created and up to 4x180 individual measured values can be displayed simultaneously. In extensions to CVM Software, an interface for C/C++ can be set up if required and cell voltage monitoring can thus be controlled even more precisely.
In duty cycle measurements, the duty cycle of pulses is measured. Each pulse consists of a pulse top and a pulse bottom. The duty cycle measurement now determines the ratio of the two quantities, which can also be expressed by the ratio of pulse duration to period duration.
Example of a duty cycle measurement
If the frequency scans for 300 nanoseconds within a period duration of 1 microsecond, the duty cycle is 30 %.
The values of the duty cycle measurement are expressed either as a ratio percentage or by a real number between 0 and 1. A duty cycle of 50 % is also called a symmetrical pulse.
Significance and benefits of duty cycle measurement
The duty cycle measurement is of great importance for the transmission of signals or modulation methods such as pulse width modulation (PWM). The benefit of duty cycle measurements is that not only an average power of the pulse strength is given, but the duty cycle also allows statements to be made about the ratio of the pulse power to the period duration. Furthermore, by varying the duty cycle, the electrical voltage and power can be controlled without power loss.
The value of many physical quantities is determined via frequency measurement, which is of essential importance for electrical measurement technology. This applies, for example, to speed, length and velocity measurement as well as to communication technology. The measuring instruments used for frequency measurement can measure frequencies of sinusoidal alternating voltages as well as rectangular signals (tilt oscillations, pulse trains).
In physics and electrical engineering, frequency is generally defined as the number of oscillations of a periodic process per unit of time. In modern measurement technology, common methods of frequency measurement include the counting method, the fast Fourier transformation (FFT) and an electronic mix with reference frequency. Accordingly, digital frequency counters, pointer frequency meters, reed frequency meters, wave meters, dip meters and absorption frequency meters are used as measuring instruments for frequency measurement.
An inductive speed sensor is a non-contact measuring method for the continuous detection of speeds. The measuring technique is based on the principle of electromagnetic induction. This means that an electric field is created when the magnetic flux density changes. For example, when a magnet moves up and down or rotates at a certain speed, an electrical voltage is induced in the coil. This can be measured at the terminals of the coil and allows conclusions to be drawn about the type and speed of the movement.
The principle of voltage induction is of great importance for applications in mechanical engineering, electrical engineering or information technology. In contrast to other measuring methods, the inductive speed sensor offers the possibility of recording rotary movements without contact and thus without wear. The measured quantity is therefore not influenced in any way by the method.
Inductive speed sensors and their fields of application
Inductive speed sensors are used today in many different areas of application:
The advantages of inductive speed sensors are to be explained using the example of the crankshaft sensor. In motor vehicles, the crankshaft is responsible for converting the translatory motion of the pistons into a rotary motion. In order to detect this rotational speed - which is equivalent to the engine speed - coils are usually used. These are wound around the soft iron core of a permanent magnet. If a gear rim is now attached to the rotating flywheel, the inductive speed sensor can determine the speed on the basis of the resulting magnetic pulses. The method is very reliable and precise, which is why it is used not only in automotive engineering but also in many other areas.
As a specialist in high-tech measurement and simulation technology, SMART TESTSOLUTIONS GmbH offers special devices for the acquisition and evaluation of incremental signals as well as freely configurable encoder simulators for use in development, laboratory and test bench technology.
A measurement system comprises the totality of all elements that directly or indirectly influence the determination of the value of the physical quantity to be measured. In detail, these are: the actual object to be measured, the measuring equipment or devices used, the person(s) measuring, the environment and the methods of measurement and evaluation applied. All these components together define a complete measurement process, which is often used synonymously with the term measurement system. Not only complex experimental apparatus is referred to as a measurement system; a single measuring device can also define a measurement system.
Measurement deviations within the measurement system and their possible causes
According to the DIN standard, deviations from the actual value of the measurement are no longer called measurement errors, but measurement deviations. This takes into account the fact that error-free measurements are ultimately not possible.
Possible causes for measurement inaccuracies can be:
In the case of measurement inaccuracies, a distinction is made between influenceable and non-influenceable errors (air turbulence, thermal noise, humidity). If the errors are constant and systematically caused, they are also referred to as offset; if they rise or fall during the course of measurement, the terms trend and drift have become established.
Because the elements of measurement systems correlate with each other as a system, errors in measurement can never be attributed monocausally to just one factor, but must always be interpreted in their interference with the totality of all elements of the measurement system.
Methods of compensation for measurement errors in measurement systems
In meteorology and quality management, a number of targeted methods for compensating measurement errors have become established. The most important measure here is the calibration, adjustment and calibration of measuring instruments to ensure the comparability of results.
PWM is a technical type of modulation. PWM is an abbreviation for the method of pulse width modulation, in which - at a fixed basic frequency - the on and off time of a square wave signal can be varied. The signal of a technical variable generated by PWM then alternates between two values. Frequency and duty cycle (ratio of switch-on and switch-off time of the square-wave signal, also called duty cycle) are variably adjustable with PWM. If the frequency is constant, the PWM modulates a square-wave pulse.
PWM is used in test systems or in test benches. PWM signal generators produce a simulated and freely scalable sensor signal that plays an important role in measurement and simulation technology.
The task of a PWM signal generator is to produce a PWM signal, whereby frequency, duty cycle and amplitude are variably adjustable. Here, the abbreviation PWM stands for pulse width modulation, a type of modulation that alternates between two values. At a constant frequency, the PWM signal generator produces a square-wave pulse.
Signal simulation is commonly used in automobile development to simulate the signal of a digital active wheel speed sensor. With these simulated sensor data various electronic control units, which can digitally process this sensor signal, can be tested either in an existing test system or at test bench. Especially the error simulation, which most signal simulation devices provide, has great importance for the development of modern antilock braking systems (ABS).
Signal simulation in practical use
By means of manipulating the sensor data realistic error situations can be simulated and control unit behavior accordingly be monitored. Especially in the development of new control units signal simulation is used to perform rapid prototyping tests, which are applied to check new control units for their interaction with existing sensors. In this case control units can easily be tested by a realistic sensor signal without having them actually be installed in a complete vehicle system.
Device-dependent functions of signal simulation
Many devices being used for signal simulation are capable of displaying several signal types (signals of cam and crank sensors and of industrial incremental encoders), each with freely adjustable speed signal curves (analogous, static, ramp-wise). The great advantage here is that signal simulation can simulate various sensors installed in vehicle by just only one simulating device.
Premium sector signal simulation technology allows to simulate failures, phase delay of several signals, patterns of swinging in and out of the engine and speed-dependent amplitude. Moreover the application of software makes it easier to configure many parametric options for displaying sensor signals, which among others affect signal pattern.
A test system is a complex network of several measuring and simulation devices that are used to test the behaviour of a technical apparatus or process under certain boundary conditions. In many cases, a test system is also set up to determine the existence of certain properties. While the result of an experiment is not known in advance, test systems serve to verify an expectation that should be empirically confirmed in the course of the test procedure.
A further difference is that experiments must be measured by the repeatability of their results, while statements that a test system can make with regard to an object or a technical device are always limited to this application. For test systems used in metrology, it is particularly important that all measuring devices have been calibrated beforehand to ensure the comparability of the devices involved in the test system.