Apparatus – measuring principle
Remote task The measurement of the load characteristic of the source is based on the standard measurement of load characteristics - shown in figure 1. It is a closed circuit in which we change the load and thus the current drawn from the source. Based on the measurement of several clamp voltage values at different streams, we can get part of the search dependency US (I ). From the knowledge of the linear form of this dependence – formula (5) – all the basic characteristics of the source can be determined. It is also possible to determine the short-circuit current without the need for a real short-circuit - it is not only unhealthy for the battery, but it can also explode in some sources (eg lithium battery)!
Fig. 1 – load characteristic of the source and measurement scheme
In order to measure the required characteristics, it is therefore necessary to vary the load in the outer circuit, measure the drawn current and also determine the instantaneous value of the terminal voltage. For this measurement, the universal K8055 USB measuring board was selected again. The block diagram of the task shows the following figure 2. The pair of K8055 analog-to-digital converters is used as a measuring part. The first of the transducers is used to read the terminal voltage of the selected source. The second converter reads the voltage at a fixed resistance in the outer circuit. The power resistor with this resistor serves not only as a current-to-voltage converter, but also serves as a maximum current limiter (preventing battery shorting).
Fig. 2 – block diagram of the electronic part of the experiment
To regulate the current drawn from the source is used one of the digital-to-analog converters, which plate K8055 is equipped. The adjustable output voltage of the transmitter is & quot; opened & quot; transistor, which limits the current drawn from the source being tested. The control range for the used batteries – alkaline and zinc-chloride – was selected in the range 0-300 mA, allowing for a relatively large part of the load characteristic. The performance properties of the components used have been chosen so that even the long-term load with the maximum operating currents is a fraction of the maximum values of the components - the requirement for 24-hour unattended operation.
In order for the task to be used not only to measure load characteristics but also to compare two sources of different design, it is equipped with two sources that can be connected to the circuit. A switching relay is used to switch the alkaline and zinc-chloride sources, either to connect the first or second source. The control of this relay provides one of the digital outputs that are also on the K8055 board.
The K8055-MARIE network management application was again used for K8055 remote control of the K8055, but this time in the new (yet trial version) version 2.5 that was developed during the construction of this remote task at the Technical Olympiad of the Pilsen Region.
Video tutorial
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