Strain Gage Webinar

Strain and pressure sensors are widely used in many measurement applications, from static to dynamic. During the webinar, you will have a chance to learn everything about Strain Gages - History, Evolution, Fundamentals and Applications.

Transcript

00:00:22 what we hope to cover during this webinar will provide not only a little historical knowledge which we believe is key to appreciate in some of the technologies that we're all exposed to on a daily basis but also an insight into how they work how they are best suited to particular applications as well as a review of some of the fundamental physics behind their use

00:00:42 we'll look at how we apply them to our measurement systems as well as how to calibrate and understand where some of the principles the variables and the constants come from and how they fit into that process finally we will have a look at some applications of these truly amazing devices we begin with a quick look at how we got here the origins of these remarkable tools and who was

00:01:04 responsible for their invention we have most likely all been exposed to some of the theories from Goerge simin home the most common and best-known electrical principle is that of Ohm's law what he actually stated was that the current flow from any conductor is directly proportional to the potential difference which we now refer to as voltage and that is inversely proportional to the

00:01:27 resistance and so all three quantities are taken care of in one go you may not be aware that this was something that he actually theorized in 1827 we now move ahead a brief period of time to the little-known Samuel Christie who was actually the real inventor of what we now call the Wheatstone bridge in fact he outlined the Delmon principle ten years before Charles Wheatstone

00:01:50 published his paper on it the problem was that while he was a reasonably well-read and recognized figure at the time he wasn't as well-known or had as many connections as Wheatstone and the rest as we know his history some folks know William Thomson as Lord Kelvin and it's very possible that if you ever have been exposed to any electrical Theory his name would have undoubtedly come up

00:02:14 to some degree he did the same thing to wheat stone as wheat stone had done to Christie by taking the credit for identifying that resistance changes in certain conductive materials when they are stretched or compressed it wasn't until 1938 that a strain gages we know it today or at least based on a similar concept was introduced Edward Simmons at Caltech conceptualized

00:02:35 as simple extensometer initially it was for impact test and surface deformation purposes in fact anyone that has ever seen a pendulum impact test will undoubtedly recognize that in Simmons original patent application where she was see on the next screen at almost the same time Arthur roogie of MIT was investigating the effects of the earthquakes in Long

00:02:56 Beach on structures and in particular water tanks he needed something that could measure the stress on the tanks and apparently had a Eureka moment and invented a strain gauge there is a twist to these two gentleman stories as they both tried to paint in almost the same device almost the same time ironically they ultimately ended up working together and can jointly take credit for

00:03:18 one of the most commonly used measuring tools in R&D you can see both Simmons and Rudy's patent application illustrations on this screen as I said before I believe that Simmons version looks very similar to a pendulum impact s as we have today a couple of things to do with these stories always makes me smile when I think about them the first is that Gorgons original theories were

00:03:43 rejected by the German physics Institute they were recognized by the British Royal Society the English equivalent the Germans physics Institute and then of course adopted as fundamental principles by every scientific Authority thereafter the reason for the rejection was actually the nomenclature the syntax the verbiage some of his peers believed that he needed to change the words he used

00:04:04 another interesting fact is that when arthur roogie submitted he's designed to the MIT patents committee they stated the committee doesn't feel that the commercial use is likely to be of major importance and declined to patent it I wonder how much they would have earned him royalties if they had not made that decision one final comment on Edward Simmons I'll urge you to do a little

00:04:25 research on him yourself as he is the classic representation of the mad professor later in life he attended meetings were in a tutu turban and tights he became known as dr. strange gage on campus for the lower part of the screen you can see some examples of some early strain gauges you'll notice that the ones that on the left of paper backing in fact the original design

00:04:51 with cigarette paper there's little point in showing every step of the manufacturing process for strain gauges but it is worth at least seeing some of it just nine of the foil use for gauge manufacturers incredibly expensive is an interesting fact in itself although it isn't pictured the process is based on about five stages foil prep and layup photo exposure itching washing and then

00:05:15 bonding or fixing the next processes are all labor-intensive they're cutting and testing gauges some of which have to be performed by hand on individual gauges it is worth meeting at this point that one of the factors that directly affect the strain gauge user is the determination of the gauge factor which is also sometimes referred to as a strain sensitivity factor or FS as well

00:05:40 as the type and grid design it also varies based on the gauge material for example Constantine and nickel chrome have a transverse negative effect while isoelastic materials have a positive effect this can vary from gauge batch to batch as we could see on the previous screen the gauges are in sheets some manufacturers refer to these as batches because it is impossible and impractical

00:06:04 to test every single gauge random selections are taken from the batches to perform the required tests noting that the selected gauges are effectively destroyed in the gauge factor determination process on the point of transverse sensitivity it is summarized by the Poisson theory for the material but it is worth being aware that there is actually a transverse sensitivity in

00:06:25 the gauge itself however this is typically completely ignored as it is generally has insignificant implications an interesting note is that the early adapters of strain gauges were not subject to the same transverse effects as they were typically round wire as opposed to the photo-etch flats of today as mentioned before the testing is determined by randomly selecting gauges

00:06:49 from the sheets or batches these are literally mounted as you mount any gauge in normal use onto a very controlled test beam in the image you can see a large number of gauges mounted on the beam in the background another step in this process that is very labor intensive is the cleaning off of all the gauges from the test beam and this has to be performed extremely

00:07:09 carefully using non-destructive methods to preserve the integrity of the beam and in the material and geometry of the beam now we get into the bit that we may want to know may already know or perhaps don't need to know and of course maybe don't even want to know but there is value in having a little bit of background knowledge for when the inevitable issues arise or somebody

00:07:35 challenges you on what you really know as we review some of the processes involved in configuring and measuring strain gauges we will see a myriad of methods which can be used to get fundamentally the same answer keep in mind that almost everyone discovers the ones that work for them and be assured that within acceptable limits each will get you to the same answer it is your

00:07:56 choice which you find easiest to apply and most comfortable for you personally I'm a believer in the simplest easiest approach so it looks simple that's the one you may want to go with professor so see frequently stated that every engineer had to be a librarian the last thing you want to do is spend all your time in the library at the same time consider the equipment that you are

00:08:21 using more modern and subsequently more powerful systems may well have all of the computational functionality to a large degree automated or built in older systems most likely had very little if any but that shouldn't stop you from wanting to know what is going on in the background and having a reasonable appreciation for the mass of physics may well help resolve issues if you run into

00:08:44 something let's start by looking at some of the fundamental stuff the nitty gritty if you will of how we use strain gauges from here on I'm going to assume we all know that a strain gauge where there are bridge is kind of pointless so what is a bridge it's basically two voltage dividers I'm sure we all know what they are so I won't dwell on this for too long but as with the image in

00:09:11 the upper left I'm pretty sure we would have seen these before the bit we are interested in is how do we construct a voltage divider into the legendary diamond form that Samuel Christie theorized in the 1830s and to get this into context and perspective by the way the first electric light bulb system was demonstrated in 1835 by James Bowman Lindsay which means Christy's theories

00:09:36 were most likely documented under Gaslight the wheatstonebridge a pair of voltage dividers that when arranged into the so called diamond configuration and provided with some known voltage provide an equivalent voltage between them that is proportionally equal to the resistances in the dividers and my new change in one represents a massive change in the global scheme of things to

00:10:03 the measured output will see later on just what that miniscule change amounts to in the example on screen you can see that the resistance on one leg has been changed this results in an imbalance and subsequently a measurable voltage at Point a the other significant advantage with this arrangement is that you can pinpoint where on the bridge the change most likely took place because the

00:10:30 polarity will potentially follow we'll look at where and why later in a perfectly balanced bridge which of course we know is almost impossible to achieve without variable potentiometers or some other electrical mechanism the measurement point represents as close to zero as it can like many measurements we make we can use a process to manipulate that relative value to provide a second

00:10:55 value for reference we call this in this case shunting and we'll look at that later we can also take advantage of newer technologies to provide offset or imbalance compensations mathematically in real time we should also mention that if the adjacent resistance has changed by the same amount that bridge would once again be in balance the two a own values

00:11:21 illustrate this on the next screen we can see a demonstration of the adjacent balance in this example you can see each resistance change and the corresponding effect that it has on the output the rule is simple as long as the divider that you are using is matched you should be able to balance the bridge switching in two opposing shunt resistors at the

00:11:46 same time would also balance the bridge but it's generally impossible when you are using measurement systems and frankly would be a somewhat pointless activity anyhow this simulation by the way was produced using a free circuit simular called circuit j s free which is as the name States free it's worth the download even if you only use it to prove your understanding of bridge

00:12:09 principles and it's free so it's worth every cent this short video demonstrates the use of the circuit jeaious emulator to replicate how the various shunt values function and what happens when you change the resistance on different legs of the bridge the changes of the resistance are unfortunately pretty coarse in this particular piece of

00:12:31 software but it still demonstrates the effect of the tension and compression of a strain gauge pay attention to the polarity changes as the variable potentiometers are changed now let's take a look at the actual implementation of gages sometimes just one we know this as a quarter bridge a single gage located on some sort of material assuming that your measurement

00:12:58 system will allow you to I say that because some systems do not offer an input voltage to be practical on certain materials for example placing a strain gage on a section of plastic would soon become problematic if the lowest excitation you could provide with say 10 volts a strain gage doesn't just look like a small electric heater it is a small electric heater where there is a

00:13:22 current there is heat the current is very small but there is still heat in some materials the surface can be affected by the heat and plastics it can literally mean that your gage is now on top of a small lake ironically this is something we've seen too many times you might recollect the blue formula in the lower right from an earlier screen this is another example of having a handful

00:13:49 of approaches that you are comfortable with and keep them in mind the formula can then be rearranged to suit the available information note the output based on the calculation would be around 0.5 millivolts per volt that is based on the K being - and the target being 1000 micro strain or micrometers per meter depending on your preferred unitless measurement system also notice that in

00:14:15 the upper left-hand corner there is a clear indication that a quarter bridge cannot offer any thermal compensation let's take a look at the half bridge it is a method of gauge application that can actually have multiple purposes for example the gauges could be placed in the same direction and effectively double the output depending on where in the bridge you place them since it is

00:14:36 possible to effectively subtract the load from each other if you aren't careful about bridge locations or they could be perpendicular to one another and be used to subtract a parasitic component or as in many applications in a location where they won't be subjected to the loading conditions but will be subjected to the same thermal events in this case they're guaranteed method

00:14:58 to remove the thermal component in some cases these are referred to as dummy gauges as they're placed onto an unloaded specimen of the same type as the measured one pay attention to the breech factor when you do your equivalent output calculations as this is relative to your gauge arrangements we'll review that later but one that shouldn't be confused as a half bridge

00:15:19 is the dual quarter bridge this is two gauges in series on the same leg in this illustrated case the output is about 1 millivolt per volt again assuming the arrangement is correct since 0.5 times 2,000 is 1,000 and the units and micro volts therefore the output is 1 millivolt per volt the four bridges by father arrangement that will provide the greatest

00:15:42 sensitivity because that's with one leg changing resistance at a quarter bridge the full bridge effectively could have all four as you can see in the image in the upper left and it has thermal compensation as the opposing legs will be subjected to the same thermal events and therefore will subtract the thermal offset in this case the output will be two millivolts per volt as there are now

00:16:02 four components to the calculation 0.5 multiplied by 4000 is 2,000 micro volts therefore 2 millivolts because we are believers in the simple approach to all these calculations we actually want to simplify them even further we can send you a copy of a spreadsheet that we put together that does all these and a bunch of others that you're going to see we'll talk about that at the end of the

00:16:23 webinar you may hear the words parasitic dummy gauge your even compensation arrangements what these all really mean is that there are a number of layouts that can be used to accommodate all of these cases in the lower-right you can see an equation normally associated with pass on half bridge the strain components are normal strain in the bending strain even though the image

00:16:44 shows four gauges unfortunately I didn't have one showing just the to the shaft equation has the torsion strain component from a fall bridge as per the image the screen is really just to illustrate some of the alternative arrangements and types of gauges such as the herringbone versions on the upper image if the bending moment was considered parasitic it could be removed

00:17:04 to a large degree one of the greatest concerns you may encounter is the thermal implication the example in the lower left was suggested by John Miller and it's actually a slick way of removing that effect from multiple points in one go possibly in real time if your system can handle it as well as the single dummy component you could dedicate a single channel as a reference

00:17:25 point in this case a dummy specimen is instrumented and measured along with the measurement points this is their mathematically subtracted from all of the other channels as the data is being recorded in this screen I'm trying to emphasize the relationship between the polarity and the behavior of the strain gauge as the gauge is stretched that's in tension

00:17:45 the resistance increases and so the output voltage increases if the gauge is squeezed that's in compression this reduces the resistance and the voltage decreases I always find the comparison to fluid flows useful to explain resistance if we reduce the diameter of a pipe the flow ease to some degree restricted as you stretch the gauge you are basically reducing the

00:18:08 cross-sectional area and so the flow is reduced inversely if you compress it the cross-sectional area is increase and thus the fluid flows more freely in this case the fluid is of course or electrons ironically early experiments are all done using some cylinders which would be similar to the pipes that you use for fluid and yes I know that the bridge system in the water analogy would have

00:18:32 to have the water flowing backwards at some point but it's still a good analogy if you consider the flow from a restriction point of view but nevertheless I wonder how many of the early theories evolved because Kelvin for example saw that very analogy before we get on to the application side let's have a quick look at wiring strain gauges when you see a strain gauge you

00:18:55 will almost only ever see two solder points or two wires hanging off or pre-wired gauges in reality you could just wire your excitation in your signal return for a quarter bridge that's a single gauge but this creates a few significant issues not least of all and absolutely guaranteed imbalance because your wires have resistance most water systems offer at least a minimum of

00:19:17 three wire connection this is usually supported by a dedicated quarter bridge completion line some systems also have a sense line system so on a quarter bridge the two become for the benefit of the sense lines is the system will actually measure the voltage at the bridge and compensate for variations these of course could be caused by thermal events on the wiring itself after all the wire

00:19:41 is potentially being expanded and contracted by thermal events and these may be some distance from the actual measurement location when we look at some of the resistance changes - the Alper later on they should put this into perspective now and how they work is great but actually using them is the ultimate objective so let's take a look at

00:20:02 configuring the various gauging bridge arrangements we'll use one of the most advanced software platforms to demonstrate a variety of different approaches this first image illustrates a point that we made earlier about the perfect world as you can clearly see there is an offset this is always to be expected if there isn't one there actually may be

00:20:22 something wrong with your bridge although chances are if there is it will be railed in one direction or another which should be a clear indication it's always good to be able to see this as you're setting your channels up so that you've got a clear idea of where you're starting from starting with the method is often associated with being calibration method

00:20:42 as opposed to a calibration check although there will be times when this is as valid as almost any other calibration approach the shunt method basically changes resistance on a leg of the bridge by very accurate amount note the use of the word change as opposed to an absolute value this would only be the case if the bridge is perfectly balanced of the gate we already mentioned that

00:21:04 and of course a couple of times that that's very unlikely the good thing about imposing a shunt value is there if the mathematical results deviate from what you observe again you have an indication of a potential problem the calculation Illustrated is probably the easiest one to remember it's the go-to one that I use every time you probably know the gauge resistance RG in the

00:21:28 formula the gauge factor carry in the formula and you can add the bridge factor BF in the formula based on the arrangement one for a single gauge in this example and the tion RS in the formula is whatever you have available to you on your system as you can see some more powerful systems offer more than one shun as well as options for locations to impose it on

00:21:52 the bridge this means you can check more than one leg using the calculation described previously you can calculate what the equivalent should be using the formula we saw in the previous screen and can see on the upper right of this screen we can estimate mathematically what it is supposed to be and then see what it measured this is another formula that's

00:22:12 available within the spreadsheet we spoke about previously some systems actually let you see the shunt value live as you test it as you can see in this example and if you missed it in this system you can always switch it in later and view it from the main channel screen if the system you are using is advanced enough it may even give you a warning or some feedback on

00:22:33 the result of the check you may catch a deliberately bad value later on if you watch carefully you'll remember the mentions of lead wire something that was frequently set aside as of less than great concern in years gone by here as with the ability to use multiple shunt values in multiple locations some systems also offer you the ability to manually accommodate lead

00:22:58 wire resistance and even measure it and tell you what it is by the way just as an example the 28 gauge six strand is typically about six to seven ohms per hundred feet an important aspect of this function is that it is primarily intended for the calibration step as any variance in lead wire resistance can be accommodated to a large degree by taking advantage of sense lines where they're

00:23:23 available notice the offset indication that was visible previously oftentimes this is something that is required as a comparison to the balanced value from time to time you may encounter a sensor that has a shunt value related to a calibration performed on the sensor by the manufacturer this is one of those moments where it would be nice if everyone agreed to say a hundred and

00:23:47 seventy four point five K ohms shunt was the standard but alas they don't and they probably won't so here are some solutions it may be that the sensor shunt simply isn't available on your system advanced systems have this incorporated into the software as does the example you can see on the screen in this case you can enter the equivalent and it calculates the match for you and

00:24:09 or the formula described here it could be used as an alternative if you prefer to do this yourself but just see what it was supposed to be and use that as a test to what you actually measured this particular software or actually reports the measured bridge resistance as well in the field where you select the bridge value adds an additional note adjacent to it specifying what it measured so if

00:24:32 the sensor manufacturer forgot to mention what the nominal resistance was you will have it readily available for your equivalent calculation it may save you they need to make the phone call to the manufacturer in order to get that value and by the way this is yet another formula that's included in the spreadsheet hang around and tell the end to get information on how to get your

00:24:52 copy we already mentioned the Poisson ratio because it's an integral part of some calculations for certain gauge arrangements this is to illustrate both where it came from and how you can calculate what it is if you have a test stand to perform the experiments on we have also included in the lower-right are proportional calculation based on

00:25:11 known value targets using a cross on formula if you need it ironically a lot of folks use 0.3 as a reference and it does cover a large number of metals but as you can see in this chart this number can change quite dramatically even on what appears to be similar materials for a later reference you may want to make a note of the value for concrete in the upper left

00:25:35 again if the system that you are using is advanced enough it will have an option to add these values or even simply select a material from a list now it's on this screen the breech factor is also available the bridge factor is something that can cause some confusion as it relates to both numbers of measuring elements and the orientation of them some baseline

00:25:56 typical numbers are simple to remember a single gauge is always one unless of course you've got the gauge at some odd angle at which time you probably should be looking at replacing that gauge anyway gauges in the same direction are usually simply the sum of the number of gauges keeping in mind that you can effectively cancel measurements there or if you wire them incorrectly

00:26:17 perpendicular gauges are usually 30% of the primary direction and so as you can see in the illustrations single gauge one two gauges in the same direction wide correctly two two gauges one perpendicular to the other 1.3 and so on and so on another great calculation to remember is the simple bending beam the nice thing about this is that the formula cuprates

00:26:41 both dimensional information as well as young's modulus there's a great way to confirm what you were doing is right it's the sort of test setup is one of the easiest to create in your own lab in addition recreating this experiment can help understand things such as breach vector and cross on ratio by simply adding more gauges some of which could be perpendicular then you could back

00:27:01 calculate to the output and again as opposed most of the formulas we have this one in the spreadsheet since we previously spoke about elastic modulus or young's modulus as most people refer to it it's nice to see where the number actually originated it is the basis for almost all materials based testing there at we have no benchmark for threshold monitoring it gives us the markers that

00:27:25 we need to determine whether something is within boundaries and a considered safe or less likely to result in for example a catastrophic failure the nice thing about Young's modulus is that there are many ballpark numbers readily available these can be found easily but don't forget that material properties can change even during well-regulated and extremely consistent

00:27:45 manufacturing processes if the system is capable of performing the conversion into the Youngs modulus and it can convert the strain to stress in real time strategies young's modulus x measured strain the epsilon this could be a large time savers this is one of the steps that could be required for many of the fatigue analysis processes that are often performed immediately

00:28:07 after data collection the rosette is a means of determining the principal stresses strains and their directions on your specimen as well as almost any arbitrary angle they are in it's difficult to determine shear stresses without these devices well where the math is pretty intensive to resolve these there is a good chance that your software will resolve these

00:28:27 for you in some cases if the system is powerful enough it can do this in real time as you collect your data in these cases I would recommend that you still preserve your original data those anomalies can cause some confusion some systems record the original data as a matter of course anyway young's modulus is required if you're using rosettes as results are

00:28:46 typically resolved as stresses as well again the method looks relatively heavy duty and you may never really care much for what is going on but as with many of the formula associated with strain gauges it's worth at least seeing it now one point i would like to make while we're on the screen is that rosette gauges are all individual channels now this may seem a little crazy to some

00:29:08 folks for me to even say this but you would be surprised how many times we get asked the question where a particular rosette element has to be installed in their bridge arrangement if the system you're using is capable of resolving the rosettes in real time this can greatly reduce your post-test analysis as well as provide real-time feedback this can be a substantial time

00:29:29 saver as you can see effects as they happen as well as remove the need for extensive data process in post acquisition some people who take advantage of this ability actually identify specific areas of concern and remove unnecessary gauges from their acquisitions as they go this ultimately reduces the amount of data you have to manage handle and analyze

00:29:49 after the collection exercise in this example you can see that the principle strains and wrong misses are being gathered simultaneously with the original rosette strain channels by doing this you can check to see if there are anomalies and perhaps even rerun rosette analysis post tests to round up the show we'd like to share a few examples of gauges in action it

00:30:13 really is just to inspire new users and provide an opportunity to see how other folks are using them the classic application for strain gauges is of course transducers themselves in fact you can consider any strain gauges laid onto any specimen as effectively modifying that specimen into a transducer an interesting fact is that the ratio of strain gauge based sensors

00:30:36 to all sensors used today not including temperature measurements is well over 50 percent pressure sensors load cells will force transducers some accelerometers and a myriad of other types are basically strain gauge devices as an example and will force transducer the number of strain gauges can be many tens of gauges the example Illustrated has 32 gauges visible in the drawing the photo

00:31:00 is a Michigan scientific well force transducer on a motorcycle it's worth noting of course with all force transducers that most of the will force transducers resolve the forces and moments for you so you're not actually measuring a strain gauge per se the custom load cell example in the upper right has a mass of gauges to remove the parasitic components and provide the

00:31:20 greatest output in the axes in which the device is intended to measure as you can see there are a large number of gauges mounted on it the load or pressure sensor in the lower left illustrates the gauge layout to achieve the maximum output the surface contact some sense are similar to that one actually have circular strain gauges to cover the entire area available for

00:31:41 the measurement the example on the left is a military vehicle with gauges located on the frame for durability monitoring there was gauges actually placed all over this particular vehicle the one on the right is an aerospace application that has a mass of gauges in a fairly small area and really just illustrates the need to get elaborate for some measurements

00:32:02 in these images you can see the surface preparation and the care taken to align the gauges in a specific orientation the directional outcome is rather meaningless without precise knowledge of the individual elements alignment in the first place some software actually has pictorial references to these as you saw earlier so that you can actually relate them back to the angle pictorially as

00:32:21 well as by the reference that you've applied to them another point of interest here is the placement following the rules regarding the placement of the gauges two welds we all know the world is likely to be an early failure point and placing gauges too close to them has a number of implications one of which is that if a gauge is a top of crack it won't see loads the same way as the

00:32:42 crack has already relieved the material of the loading effects the other one is the world's caused changes in the materials that are typically very localized and can initiate micro cracks due to the thermal contractions the individual gauge on the lower right may well have been placed because previous testing had already identified the angle with the highest load shear was probably

00:33:02 already previously described so a single gauge could be used to reduce the total amount of data collected John one of my fellow App Engine ears he's very proud of his micro measurements trainee specimen so he should be you can clearly see that he went to great lengths to ensure surface prep was thorough and honestly that is some of the best soldering I've seen in

00:33:20 a long time I'm assuming they weren't pre-wired gauges the other examples on the screen are also compliments of John with his civil engineer background he has been called upon many times to help with instrumentation on projects where materials such as concrete's are involved you may remember my reference some time earlier regarding the poisson component differences those unfamiliar

00:33:39 with the snoer gauge work will probably notice that some of the gauges are extremely long this is because of the properties of the material in it reinforces the aspect of gauge selection in respect of the material that you plan to apply them to the SIRT their surface structure and density of concrete is a macro version of aluminum and other alloys so the gauge is grow

00:33:56 proportionally in length to the structure as you can see some of the gauges are embedded in the concrete to determine the properties of that particular mixture you may seem similarly embedded uses carbon fibers and some plastics but keep in mind that strain gauges and temperatures well they don't mix very well only with specialized gauges can you place a gauge

00:34:17 into something that potentially was molten such as a plastic for example so be careful about gauge selection when performing those kind of exercises the shafts that you see in the upper left and center are examples of measuring strain gradients on very different materials again note the significant difference in gauge length between the two examples in the lower

00:34:40 left or rosette gauges on a rollercoaster used for dynamic analysis of a bracket we've previously observed failures it's nice to know that they were looking into the cause hopefully the in with the intention of preventing any accidents the lower center is actually a homemade transducer it was used to determine damping coefficients of various materials for dropping large

00:35:00 weights in a workout area I wonder if the large weights were the people who possibly needed to be in the workout area the lower-right is a strain gauge project involving a utility pole measuring strain and stress of it as the sections were seated into one another the master gauge applique you see is actually our very own John Miller although he claims anonymity by wearing

00:35:21 the proper safety equipment which I guess is a good thing on the left you can see another view of the same utility pole as well as John attempt into a photo bomb in the same white helmet in the background the illustrates the position with which gauges need to be placed even on large specimens the final image on the right is an aerospace project which as with

00:35:41 many high-cost installations has a mass of different sensors applied some of which I'm told a strains I can't personally see them but that may be a good thing may increase providing the image and assures me there are gauges in there and so we're open to that we're going to open the challenge to see if you can find them in that jumble of cable sensors and hardware

00:36:01 so this is the final screen and it's basically the spreadsheet that we have alluded to a number of times during the webinar it contains virtually every calculation we were referred to during this webinar as well as a couple of others and each illustrated with a pictorial representation of the application and the values in each of those images is

00:36:20 updated as you change the parameters so you get a pictorial representation of what you're doing and hopefully that'll make some of this a little clearer so if you would like a copy of this rather useful spreadsheet just contact your local representative all the support guys and we'll be happy to pass it along to you now it doesn't contain any macros so it probably won't get stopped by a

00:36:40 firewall so hopefully you'll get your copy so thanks very much do I stop you as I would like to thank you for your time and we do hope that you found something of use or of interest in this webinar we are now going to open it up for questions and answers with John Miller main quest and myself Dave gallop and also please let us know remember what I

00:37:06 said at the beginning please let us know if you'd like to see something in particular in the future we'd be more than happy to to consider that and certainly if enough people ask us maybe we'll be compelled to do it so please feel free to ask your questions now otherwise thank you so much for your time and don't forget contact us if you want the spreadsheet

00:37:33 you