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Farrell Edward Jeremy Davia Jason Fox Assembly: Before you can even begin the assembly of a foil-type strain gauge, you must first be aware of the safety precautions. During the assembly, a bonding agent called superglue will be used to bond the gauge to the aluminum beam. This super glue is adhesive to many materials including skin and eyes so care must be taken if using bare skin during application. When starting the assembly procedure, all surfaces were smoothed and cleaned, as to make the most suitable bonding surface. First, the strain gauge was positioned and bonded in the center of the beam on the top surface. Next, the gauge was picked up with some cellophane tape and aligned to where it was to be mounted. Glue was applied gauge was adhered while being held down with an eraser. After that, a strip of masking tape was put under the gauge wires as to keep them from contacting the beams surface. Lastly, a solder pad was glued next to the masking tape and then the gauge wires and lead wires were soldered to the pad. Testing Method: In the testing, the gauge was secured to the desk and the lead wires were connected to a full Wheatstone bridge configuration. The bridge was excited by a 10.0V power source. Due to unstable readings that may have been due to potential overheating of the gauge wires, the voltage was decreased from 10V to 5V. The bridge was also connected to a multimeter that measured the differential output voltage of the Wheatstone bridge. The first tests included stacking the weights on the unsupported end of the beam. This was a challenge because large, heavy weights had to be stacked on a 1"x3/4" platform. The second test was with an aluminum 2"x 2" platform screwed into the unsupported end. This was much easier because the weights could be spread out and did not need to be dangerously stacked. However, some peculiar readings were observed when using the platform. A probable cause was that the platform enabled the weights to flex the gauge along its transverse axis. The test with the platform was repeated, stacking the weights on the center. After the three trials, the data was collectively put together in charts and equations. Testing Results: Data from the initial testing at 10V was completely discarded due to the fact that values were irregular due to not having weights placed on the center of plate. The procedure for the testing was to start at 0.5 lbs, take a reading, and then increase the weight by another 0.5 lbs. Now the tests were run with the plate on, but the weights not stacked. At 0 lbs. the nominal resistance of the system was 835 . Fig. 1 shows the results for the first test. After graphing these numbers we immediately found that these number should have been following a linear pattern, but weren't. Testing with plate, but not stacked 1800 1600 1400 1200 Vdiff 1 uV Linear (Vdiff 1 uV) y = 139.81x + 871.6 R2 = 0.9223 Fig. 1 1000 800 600 400 200 0 0 1 2 3 4 5 6 Since the measured relation was not linear, as was expected, the test was not repeated. The second test did not involve the plate screwed on top but instead the weights were to be stacked onto the 2"x 1" end of the bar stock. This time the nominal resistance was 908 . The results from this second test were more linear. The plot of the graph had significantly less deviation from the linear line. The slope of the line for this test, which was very close to each of the actual data points, was y 127.76 x 918.19 and the proportion of variability in the data set was R2=0.9956, which indicates a linear relation.. Testing without plate, weights stacked Fig. 2 y = 127.76x + 918.19 2 R = 0.9956 1800 1600 1400 Resistance 1200 1000 800 600 400 200 0 0 1 2 3 4 5 6 7 Vdiff 1 uV Linear (Vdiff 1 uV) Weight(lbs) During the first test, the weights had been irregularly spread out on the plate, and did not keep the strain on the sensing axis alone. The weight on the edges of the plate twisted the bar so that some strain was put on the transverse axis; this was probably the reason for the non-linear readings. This conclusion prompted another with test the plate attached, except still stack the weights on the center as to keep the strain along the sensing axis. In this third test, the relation was now more linear and supported the hypothesis that placing the weight consistently in the center of the plate was important for accurate readings for the strain Test with plate, Stacked 1800 1600 1400 y = 131.31x + 928.36 R2 = 0.9922 Resistance 1200 1000 800 600 400 200 0 0 1 2 3 Weight(lbs) 4 5 6 stacked Linear (stacked) Fig. 3 gauge. Notice how the proportion of variability in the data set is now R2=.9922? The closer that number gets to 1 the more accurate the line is. Regarding the elasticity of the beam, the nominal resistance at the beginning of the third test was 921 . After applying the first weight and removing it, the nominal . After the third weight trial, the nominal resistance was resistance now became 919 915 . This steady increase in nominal resistance continued with each weight, suggesting that the system was not completely elastic. This would mean that the readings would not be repeatable. Once connected to the digital meter, the Strain Gauge had an odd, yet consistent pattern to it. With no load, the voltage started at about 835 micro volts. Once weight was applied to the system, the voltage spiked to its peak and then started to decline slowly in micro volts. So in order to keep consistency, a time of ten seconds was waited out after applying the weight and before taking the reading. Once the weight was removed, the voltage went back down to around its original or nominal state then started to climb slowly again. Also, the way the weight is stacked on the beam is a factor. With the plate, if the weight was spread out across it, the reading was not that accurate, however, when the weight was stacked up in the center of the plate completely vertical, the reading was much more accurate and fit well in the graph. Overall, it is a good idea to use the 5V power source instead of the 10V, even though it climbs slowly. Excitation at 5V resulted in more stable measurements, as compared to 10V. Budget: Parts Price Description Aluminum Strain Gauge Resistors (3) Krazy Glue Solder Copper Wire $1.25 lb. $5.50 ea. $0.10 ea. $0.02 ea. $0.11 ea. $0.0075 ea. Average price over a 7 day period Come in packages of 10 Watt Carbon Film Resistor For 2 drops of Krazy Glue For 2 inches of 0.030in. solder 2 inches of 18AWG copper wire Table1: Budget of materials needed The above budget is based on internet ordering services per load cell. The aluminum price is the average price for aluminum over a seven day period xy scatter chart. The strain gauge has a nominal resistance of 350 ohms and is from OMEGA Engineering. The resistors that we need are really only need to be 5 watt, however, by using a watt resistor, it leaves more room for error incase more voltage is applied to the system. The Krazy glue and solder is standard for any project. The copper wire that is needed is around twenty gauge, however, by buying eighteen gauge wire, it will allow more current to flow making the measurements more accurate. Discussion: This design meets the project targets as well as ignores the problems that won't affect the system. This design will be able to measure the weight of a bird using changes in electrical resistance from a strain gauge. The range of weight is 0 lbs. to 5 lbs. which will cover the weight of many species of bird. The design is also an independent system and can be left alone unattended running off its own power source. Being that this system has to be camouflaged, it is good that it is small and compact. This feature also enables it to be able to be transported and set up very quickly. Overall this is a good design solution for the problem. It is affordable, easy to implement, and easy to understand when using. The only changes that might need to be made depend on the systems surroundings and environment. If the system will be implemented in an environment with a widely varying temperature, consider using a full Wheatstone bridge instead of a .

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