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Use a sensor to make a measurement.

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Introduction In my coursework, I am going to use a sensor to make a measurement. The sensor system is intended for use as a lightmeter for a photographer to detect light. I have chosen to find the respective voltages for variance of illumination on a LDR (Light dependent resistor). Things needed Two D.C. power supplies, a variable resistor, a bulb, a LDR, a 1.6 k? resistor, a voltmeter , two crocodile clips and a luxmeter. Setup The variable resistor and the bulb are connected in series to one of the power supplies. On the other hand, crocodile clips are attached to the LDR for better conductivity. The 1.6 k? fixed resistor and the LDR are then connected in series to the other power supply. The voltmeter is connected in parallel across the LDR. The luxmeter and the bulb are positioned close to the LDR on a similar level to avoid making wrong measurements. The whole arrangement is shown in the diagram below: Setup Diagram A Circuit diagram is also enclosed. Process Both the D.C. power supplies are switched on. The initial measurement of the power supplies is taken to ensure that readings by the voltmeter are sensible. ...read more.


So a 1.6k? fixed resistor was used to avoid accidental blowing up of the bulb. * The voltage across the D.C. power supply i.e. 5 V was found simply by connecting the voltmeter to the D.C. power supplies and not including any other instruments. * A measurement of the background illumination was found with the luxmeter while the bulb was switched off. This background illumination is NOT subtracted from the values of my lux readings that follow, since it is not possible to have an illumination-free environment due to sunlight other than a dark room. Table Measured lux Mean lux Voltage reading Mean voltage (in lux) (in lux) (in V) (in V) 1070 -1080 1075 3.66 3.66 1010 -950 980 3.63 3.63 830-840 835 3.5 3.5 720-730 725 3.46 3.46 660-670 665 3.42 3.42 610-650 630 3.35-3.37 3.36 580-640 610 3.35 3.35 550-640 595 3.36 3.36 600-640 620 3.35-3.37 3.36 590-640 615 3.35-3.36 3.355 580-640 610 3.34-3.36 3.35 620-640 630 3.32-3.34 3.33 390-400 395 2.04-2.06 2.05 150-220 185 1.95 1.95 350-400 375 1.76 1.76 10 10 0.05 0.05 READINGS 1 The formula used for finding the mean values wherever necessary was (READING 1+ READING 2) ...read more.


someone passed in front of the sensor on the LDR), different readings were obtained for the same illumination. All measurements were made from the same position and all obstacles were cleared. Luxmeter suddenly increases in value and switches off to save power. The luxmeter is switched on even while it is on and then the readings are taken. Safety concerns * Due to safety concerns, D.C. power supplies were used instead of A.C. power supplies.Extra low voltage DC is safer than AC. Anything less than 120 volts DC is not considered lethal, whereas with AC you need to come as low as 32 volts! * Care should be taken with the eyes. Even though the voltage of the bulb used in the experiment is small, looking at the bulb for a short time even when taking down luxmeter readings can cause eye strains. To reduce this effect, a retort stand with a barrier can be set to obstruct the light from the experimenter's eyes (but not the LDR or the luxmeter). All electrical equipments and connections should be handled carefully and only disconnected from the circuits when the power supplies are switched off. Acknowledgements The following source was used for a part of this coursework relating to the safety concerns of D.C. over A.C. http://www.rpc.com.au/products/efn/efnextracts/remote.html- D.C.than A.C. ...read more.

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