* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download TEP Ohm`s law with Cobra4 Mobile
Survey
Document related concepts
Power electronics wikipedia , lookup
Superconductivity wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Josephson voltage standard wikipedia , lookup
Negative resistance wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Rectiverter wikipedia , lookup
Surge protector wikipedia , lookup
Power MOSFET wikipedia , lookup
Thermal runaway wikipedia , lookup
Opto-isolator wikipedia , lookup
Current source wikipedia , lookup
Current mirror wikipedia , lookup
Lumped element model wikipedia , lookup
Network analysis (electrical circuits) wikipedia , lookup
Electrical ballast wikipedia , lookup
Transcript
Ohm’s law with Cobra4 Mobile-Link TEP Related Topics Ohm’s law, Resistivity, Contact resistance, Conductivity, Power and Work Principle The relation between voltage and current is measured for different resistors. The resistance is the derivative of the voltage with respect to current and is measured in dependance on current. In case of an incandescent lamp the temperature rise with higher current leads to a considerable higher resistance. Equipment 1 1 1 1 1 1 1 1 1 2 2 Cobra4 Mobile-Link incl. Zubehör Cobra4 Sensor-Unit Energy Digital Function Generator, USB, incl. Cobra4 Software Connection box Resistor 100 Ω, 1 W Resistor 220 Ω, 1 W Resistor 330 Ω, 1 W Lamp socket E10 Filament lamps, 12 V/0.1 A, E10, 10 pcs. Connecting cord, l = 500 mm, red Connecting cord, l = 500 mm, blue 12620-10 12656-00 13654-99 06030-23 39104-63 39104-64 39104-13 17049-00 07505-03 07631-01 07631-04 Additionally required 1 PC with USB-interface, Windows XP or higher Fig. 1: Experimental set-up. www.phywe.com P2410162 PHYWE Systeme GmbH & Co. KG © All rights reserved 1 Ohm’s law with Cobra4 Mobile-Link TEP Set up and procedure The experimental set-up is shown in Fig. 1. Connect the Cobra4 Mobile-Link to the USB-interface of the computer and plug the Cobra4 Sensor-Unit Energy onto the Mobile-Link. Connect the Digital Function Generator to the Sensor-Unit and the USBinterface of the computer. Load “Ohm’s law” experiment. (“Experiment” “Open experiment”). All presettings that are necessary for data acquisition are now carried out. Click on in the icon strip to start measurement. A sample measurement is given in Fig. 2. Fig. 2: Current curve of an incandescent bulb. 2. Resistance measurement Now put a resistor into the place where the bulb had been. Record a curve again. You may put several curves into one diagram with “Measurement“ “Assume channel...“. The curves may look like this (see Figs. 3 and 4): Fig. 3: 2 Current-voltage diagram of commercial resistors Fig. 4: The power dissipated as heat in the resistors PHYWE Systeme GmbH & Co. KG © All rights reserved P2410162 Ohm’s law with Cobra4 Mobile-Link TEP Theory and evaluation 1. Incandescent bulb With the “Regression“ tool of the “measure“ software it is possible to determine the resistance of the bulb at different applied voltages. E.g. around zero Volt the slope of a slowly measured curve is 90 mA/V, thus is the resistance of the bulb 11.1 Ohm at room temperature. A check with an ohmmeter yields 11.2 Ohm. Around 9 Volt is the slope about 5.6 mA/V and that yields a resistance of 179 Ohm, sixteen times the resistance at room temperature. The curve is not symmetrical because of the heat capacity of the bulb. When increasing the voltage, a part of the dissipated energy is necessary to warm the bulb and so the temperature is not the same as with the same voltage when decreasing the voltage. If the curve is recorded very slow, the state of thermal equilibrium is better approximated and the curve gets more symmetrical (Fig. 6). You can do so by setting the “Pause time“ in the function generator’s parameters to some seconds (Fig. 5). The rise of resistance with temperature in metals is due to electron scattering at phonons, the quanta of crystal lattice vibrations. The rise can only be considered to be linear for small temperature changes. Fig. 5: Function Generator settings. Fig. 6: Curves recorded with different speed. 2. Resistors The resistors for industrial use are usually metal film resistors or carbon resistors. The thermal coefficient of them is usually 0.025%/K or 0.0125%/K. The allowed power dissipation specified for them is such that www.phywe.com P2410162 PHYWE Systeme GmbH & Co. KG © All rights reserved 3 TEP Ohm’s law with Cobra4 Mobile-Link they don’t heat up much. Here no deviation from linearity can be seen – the resistance stays the same over all the range of the meaurement and they follow Ohm’s law, with resistance R, current I and voltage U. The slopes read out with the “Regression“ function are for the 330 Ohm resistor: 3.04 mA/V 220 Ohm resistor: 4.65 mA/V 100 Ohm resistor: 10.14 mA/V and this yields 329 Ohm, 215 Ohm and 98.6 Ohm, respectively. This corresponds well with the manufacturer’s data and the 5% tolerance specification for them. 4 PHYWE Systeme GmbH & Co. KG © All rights reserved P2410162