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Let us continue our discussion on strain gauges. We have looked at in the last class, strain
gauge as a system consisting of the metallic grid supported by a carrier and which is bonded
to the specimen by a suitable adhesive. We have looked at quick setting adhesive like
cyanoacrylate; then, we looked at epoxy, which is meant for sophisticated installations like
in transducers, where you need to provide a very thin bond line, and also, it should
come for longer periods of operation; then, we looked at polyester adhesive.
Now, let us look at the ceramic cements; and when you look at ceramic cements, they are
useful for high temperature application or in radiation environments. See, now nuclear
power is becoming very, very important; so you need to live with radiation environments
in such installations. And in such applications, organic adhesives cannot be employed; so you
need to necessarily go for ceramic cements; and one of the popular ceramic cement is NIST-x-142,
which exhibits high resistivity up to 980 degree centigrade.
We have earlier looked at some of these common alloys, advance and karma, they can go up
to 260 degree centigrade, that is only their metal foil and the associated carrier we will
looked at was polyamide or epoxy or any such carrier. For any one of the high temperature
application, you need to find a suitable metallic foil, as well as an adhesive. Now, we are
looking at the adhesive. We will also look at the special type of strain gauge, and also
the special process by which you could spray the ceramic cement.
And what you have here is, the constituents of NIST-x-142 is listed here: you have alumina,
you have silica, you have chrome anhydride, and you have a colloidal silica solution,
and you also have orthophosphoric acid.
So, what you have here is, you have the blend of ceramic powders such as alumina and silica,
combined with the phosphoric acid is mixed with a solvent such as isopropyl alcohol and
an organic binder to form a liquid. So essentially, you have the ceramics available as a liquid,
so that it is easy for you to apply it by a spraying process.
And what you do is, on the specimen, you provide a pre coat of the ceramic cement. After application,
it is fired to form a thin layer between the gauge grid and the component. So, it is a
very elaborate process; you need to have a proper training to handle this kind of special
cements. So, once you form a thin ceramic cement layer on the specimen, you place the
gauge; and the gauge is also very special, we will have a look at it a little while later,
and what you have is, you have to remove the carrier of the gauge and place it on the thin
layer of ceramic and a second layer of ceramic cement is then applied. So, you have initial
layer of ceramic on the specimen; your normal carrier of the gauge will not withstand such
high temperature. So, the carrier of the gauge needs to be removed and you put a second layer
of ceramic cement to bond the gauge. And when you do something like this, gauge resistance
to ground will be only about 6 meg ohms; it is much smaller, but that is the best that
you could get when you use these kind of ceramic cements. So, what you see here is, you need
to have a strain gauge such that its carrier can be removed.
And you have an example of a how such a gauge can be constructed. I have a sketch here.
I essentially have a wire type strain gauge, and you have a Teflon tape carrier, which
could be peeled off, and you make a decent sketch of this. So, what you have here is,
gauges are constructed with a grid fabricated from wire, which is mounted on slotted carriers
made of glass reinforced Teflon tape. So, why you have slotted type is, you put a layer
of ceramic, then the strain gauge would be bonded, at the time you can remove this Teflon
tape; then again do a code and complete your installation.
And in order to apply the ceramic, you need to have a special gun, and as I mentioned
earlier, the tape is removed after the grid is secured to the component. So, it is a very
involved process. You know it is not like simple strain gauge bonding, since you have
to work at very high temperatures, you need to have a systematic procedure. Here we look
at one family of strain gauges, which could be used for high temperature. There are also
weldable strain gauges, which we are not paying attention now, but you should know, that for
high temperature application, you also have another form of strain gauge, which could
be welded to the base material. Here we only look at forming a layer of ceramic,
and remove the carrier, and again put another layer of ceramic, so that the gauge is properly
bonded. And you have such gauges available commercially; and this is given by a micro
measurements.
And they have what is known as Kanthal - is meant for high temperature strain gauge, and
you could see the slotted Teflon tape carrier, and you have the strain gauge available like
this; so this can be used to put the ceramic cement, and remove the carrier, and put another
layer. So essentially, you will have only a ceramic base and you have a metallic foil.
There is nothing like a polymer that comes in between; so at such high temperatures,
they will not withstand that, they will disintegrate. So in order to make sure that your instrumentation
is good at that high temperature, you form a ceramic layer.
And how do you do this application of ceramics? So you have a special gun, this is the modification
of your gas gun, and you feed the alumina as a rod. So you have a ceramic material in
rod form is fed into the combustion chamber. And because of the high temperature, the rod
decomposes into softened semi-melted particles.
And you can actually have a closer look of this. So you have the ceramic rod, you have
oxygen and acetylene, and at the outlet of the gun you have an atomized spray of ceramic
particle. That is what you get. The idea is to get a fine spray, and spray it on the specimen;
and by changing the rod, you could apply it for different temperature gauges; that also
we will see. The material that will use for the rod, if you change it, you can work for
different temperature gauges.
And what you find here is, you use a pure alumina rod for high temperature applications;
on the other hand, if you use a rod which has 98 percent alumina with 2 percent silica,
you could use it for applications below 425 degree centigrade.
So, what you have in this process is, the ceramic material in rod form is fed, and you
have an atomized spray of these particles, and the particles impinge on the surface of
the surface of the component and forms a continuous coating. Again, a very special process; it
is not a simple spray gun, you have to handle it carefully for you to form a thin layer
of ceramic. Now, what we had looked at is, we had looked
at the strain gauge system: system consisting of the metal foil, carrier and the adhesive.
Now, we will have to look at how this system functions in actual practice, what considerations
that we need to look at while selecting the constitutions of the system. Depending on
the application, I will select the suitable alloy, suitable carrier and also a suitable
adhesive. For high temperature, the selection is very simple: you know that you cannot use
epoxy or polyester as an adhesive, you need to go for ceramic cement. But even from stability
or hysteresis or linearity point of view, the constitutions play a role. You know that
is what you have to look at. And I said strain gauge selection is the very, very important
aspect that you need to learn, and for strain gauge selection, you need to have a background
- what is the role of each of the constitutions. Though this information is descriptive, that
information is also needed from the point of view of selecting the appropriate system
for your measurement.
And we have already look at… you need to worry about strain gauge linearity, hysteresis
and zero shift in any strain measurement application. And, what happens to the magnitudes of these
like deviation from linearity, hysteresis and zero shift - they all depend on various
factors: what is the strain level that which I operate, whether the bond is adequate, so
that strain transferred from the specimen to the strain gauge is effectively carried
out; and if you look at the property of the alloy, what is the degree of cold work or
the foil material, and naturally, the viscoelastic characteristics of the carrier material.
Because we say that deviation from linearity, hysteresis - they all become very important
in transducer applications, and you will find by changing the suitable carrier, it is possible
for you to improve some of these aspects. That is why I said, you should view strain
gauge as a system consisting of the alloy for the strain gauge metal foil, then you
have the carrier, then you have the adhesive. Selection of all these three are interrelated;
depending on the application, you should select it appropriately.
And what I have here: suppose I want to minimize deviation from linearity, then choose an appropriate
carrier. What you find is polyamide carriers the deviation is about 0.1 percent. On the
other hand, if I go for epoxy carriers, this just half off it - is about 0.05 percent.
But you know very well, polyamide is easy to handle. It is a plastic, even a beginner
can handle this polyamide carrier. We have already looked at epoxies bridle; that is
recommended for transducer applications. So what you find is, when I want to improve linearity,
hysteresis, zero shift, I need to go for sophistication. It comes with the price; it does not come
freely. And we have also looked at strain level plays
a role, and what is observed is, hysteresis and zero shift strongly depend on the strain
gauge. And that is what is illustrated in this graph, you can have a look at it.
So, what I have here is, on the x-axis I have number of cycles, and the y-axis you have
cumulative zero shift, and the graph is plotted for a strain range of plus or minus 1000 micro
strain; and another graph for 1500 micro strain, and the third graph for plus or minus 2500
micro strain. It is very high, it is going beyond elastic region; plus 2000 micro strain
is the strain range at which you have the plastic deformation take place.
So what you find if you closely look at, you know there is the initial slope; as the number
of cycles increased you have a radiant, and then it becomes horizontal - make a note of
it. How do you use this information for strain gauge instrumentation, what is the recommendation
- that will see now.
The recommendation is, define that the zero shift changes the initial few cycles; so you
have zero shift per cycle is much larger during the first 5 to 10 cycles, that is what the
graph shows. So what you do is, it is recommended let us strain gauge installation be cycle
to 125 percent of the maximum test strain, for at least 5 cycles. So you do not go and
make the measurement as soon as you paste it, and the strain gauge is ready for measurement.
You find that adhesives completely cured, you do not go and do the make and the measurements.
The advice is you do a strain cyclic; particularly when I making a transducer, I will do the
calibration at the factory itself, where in you will load it, and beyond 125 percent,
do a few cycles, and then ensure that the system as the whole is stabilized, then release
it for actual measurement. Even in your regular test conditions, it is recommended that you
do a strain measurement, before you make final measurement. From where thus knowledge comes?
You find the zero shift is the function of the cycle. Initially, the zero shift is more;
after about 10 or 15 cycles, it stabilizes. So the recommendation is, at least do 5 to
10 cycles. If you can do more, that is well and good enough. So that is what you get from
looking at your observation on zero shift as the function of the strain range.
Now we get on to another important issue in all strain gauge installation, add its stability.
This become very important in applications, when you have to record the strains over a
period of months or years - is not just that you do the strain measurement for immediate
requirement, and forget about it. Suppose I want to monitor structures like dams and
bridges, we may have to do it for long periods of time.
And in such applications, there may not be an opportunity to unload the specimen, and
recheck the zero drift. So in such applications, it is better that you select a system that
is stable for such applications. And when I say the strain gauge system have already
set, you have to choose the proper alloying material of the strain gauge, the type of
carrier, as well as the adhesive; all three go together. We will see a nice example where
people have conducted experimentally for a long period of time, different alloy as well
as the backing in the adhesive. When I change one after another, you find there is significant
improvement. So in applications where you have to record
strain over a period of months or years, the stability of the strain gauge system as the
whole has to be looked in to. So when I say a system as the whole, you should pay attention
on selection of proper alloying material, type of carrier, as well as the adhesive.
And you will have a nice example.
I have a graph, which shows time versus zero shift; time is plotted in a log scale; I have
10 days, 100 days and 1000 days. And I have three graphs - I have one graph for strain
gauge alloy, its advanced grid and polyamide carrier; and the second graph is the grid
material is same - it is again advanced grid, encapsulated phinolic glass carrier, the carrier
is made different, you have the encapsulation and you have the phinolic glass carrier, it
is much better than the polyamide carrier. So what you find, you see a very significant
zero shift in a simple advance with polyamide carrier, which is substantially reduced when
I just change the carrier material. And the third graph, which is almost close
to 0, that you get from karma grid encapsulated with glass fiber epoxy phinolic carrier. So
what you find here is, by changing the strain gauge alloy, what you find finally, the system
as the whole has improved. From the first graph to second graph, you found that the
carrier as indeed improved. A further improvement is possible by changing the alloy itself.
So that is where I said, you need to look at strain gauge as a system. And you have
a summary of the observation of the graph which is available in the next slide.
And what you find here is, a zero shift of the order of 270 micro strain is observed
after 30 days for advance alloy with polyamide carrier. And if you look at the installation,
installation was water proofed well - there was no difficulty of moisture entering into
it, and deteriorating the strain gauge bonding. And what people found was, the carrier is
not taking the load properly, so there was stress relaxation, which just caused the drift.
And when you are making a measurement, 270 micro strain is very high; if the zero shift
itself is 270 micro strain, then what level of confidence you will have in the final measurement.
So for a given application, you need to find out, have you selected the right combination
of strain gauge alloy, carrier, as well as the disk. And you see in stages - initially
we saw 270 micro strain, which is very bad.
Now I go and improve the carrier instead of polyamide; if I use the glass fiber reinforced
phenolic carrier, the drift has reduced from 270 micro strain to 100 micro strain, even
after 50 days. In fact, that is what is listed in this graph. This is about 270 micro strain.
This you see at the end of 30 days; and at the end of 50 days, you find only a 100 micro
strain, by just changing the carrier for the strain gauge.
So whatever the stress relaxation, the glass fibers eliminated that effect. And also the
whole test was done at 75 degree centigrade. See we have already noted that advance alloy
is the good strain gauge alloy for room temperature applications; and they also noticed, that
drift was due to instabilities in advance alloy, at the test temperature of 75 degree
centigrade. So, once you notice this, change the strain gauge alloy to karma grid, by retaining
the same carrier with encapsulating glass reinforce epoxy phenolic carrier. Zero shift
was only 30 micro second after 900 days, so that means so almost like 3 years 2 and half
years. For two and half years absolutely no problem
in your strain measurement. But when I take a karma grid, what happens - it is difficult
to solve the taps. So, you need to go for factory supplied lead wires. Strain gauge
also comes with three attached lead wire systems. So, you need to go for that kind of a strain
gauge, for you to use in such applications. So all that is expensive. See if you go and
solder your own lead wire, the costs are less. But, if you have to get the pre attached lead
wire, cost is high; and glass reinforced epoxy phenolic carrier is again expensive. So when
you find your application demands high stability, then it is what is spending money for such
applications. So you need to select, you cannot take things for granted - stability is an
issue. So you need to worry about what temperature
that you are working at, and what backing that you are using, and what adhesive. Here
the adhesive role is not emphasis that much, and what we find is karma grid as work, as
75 degree centigrade quite well - even at room temperature, instead of positive drift,
it has a negative drift of minus 25 micro epsilon.
See what you have here is for long term measurements, karma grids with glass fiber reinforced epoxy
phenolic carriers, with a well cured epoxy adhesive system is recommended. I said that
adhesive as not be mentioned, but what you find here is for any sophisticated applications,
people go for epoxy adhesive. And you should also ensure that the gauge
installation is water proofed well. You do this to minimize moisture penetration. Not
only this, see we have already seen in a strain measuring instrument, I need to have completion
resistors. The bridge completion resistors should be hermetically sealed to ensure stability
of the bridge. See the idea is, you have taken care of the strain gauge installation: you
have selected the right type of the alloy, carrier, as well as the adhesive. But now
you have to make the measurement using a stone bridge, and stone bridge has completion resistors
- because in many applications we may do only a quarter bridge, the other three resistors
are there in the stone bridge, and these have also to be waterproofed well - because you
are trying to make the measurement for long durations.
You know sometimes you may ignore this, you may take it for granted that the instrumentation
will automatically take care; so you need to go for properly shield completion resistors
for such long term applications. It is very important and this completes. So what you
find is for stability, go for karma grids with glass fiber reinforce epoxy phenolic
carrier with well cured epoxy adhesive, and also ensure in your bridge completion resistors
to be hermetically see.
Now we move on to one of the other important aspect in strain gauge instrumentation, namely,
heat dissipation. See when you come to thermal effects, you need to dealing two effects:
one is I worked at moderately high temperature than the room temperature. Suppose I want
to measure strains on a IC engines, then I may have to put it at the IC engine block,
and find out that temperature will be higher than the room temperature.
So in such applications, I should measure the temperature by a thermo couple, and then
either look at thermally induced apparent strain and subtract it; or put another strain
gauge which is at the similar temperature and make it as a half bridge, and handle the
thermal effect. This is one type of thermal influence.
The other type of thermal influence what you need to worry about, is heat generation due
to I squared R loss. This is very subtle. See in many applications, if you have working
at high temperature, compensating for that you may do it more by a routine, because that
is very obvious. What is subtle is, because current flows through the conductor, the strain
gauge itself get heated. This is a very subtle issue and you need to find out what parameter
at influence, given the selection of the grid size can make; and what is the voltage that
I applied to be stone bridge for making my measurements that also can influence. So here
again you have to look at system as a whole, and find out a remedy.
And why we need to worry about this, whatever is the I squared R loss, this causes a change
in the temperature, which in turn causes the change in the resistance of the strain gauge;
thereby spurious strain signals would be produced. So I need to eliminate this spurious signals.
And this is the most challenging aspect of strain gauge instrumentation. And from this
point of view, heat dissipation assumes importance. Whether you like it or not, strain gauge get
heated, and you need to look for how to dissipate this heat generated. What are all the parameters
that I have to look at, so that I minimize any temperature raise, because of buildup
of heat due to I squared R loss. That is the focus.
And it depends on various factors. The first factor is, what is the gauge size - if you
look at the catalog of strain gauge by the manufacturers, you will find gauges of various
width and length to suit different applications. The second aspect is, what is the configuration
of the grid and what is the spacing and size of the conducting elements? See, when you
say the configuration, I had already mention, I can have a row set with strain gauges separately
aligned, and I can also have them as tract. And from measurement point of view, the approximations
involve in idealizing the point on which you make the measurement, stack row sets are better.
But stack row sets bring in another problem - the heat generation will be much more in
a stacked row set than the normal rectangular row set, where they are kept slightly away
from the point of interest. They meet at a point of interest; they are not exactly on
the point of interest for which you want to make the strain measurement.
So grid configuration matters, and what is the type of carrier, and what is the type
of polymer, and what is its thickness. You can also say the similar thing for the adhesive;
and if you look at the specimen material, that also plays a role. Am I working on copper,
or am I working on steel, or am I working on plastics - the specimen material matters.
Not only this - I may work on copper, or I may work on steel, but even the specimen volume
at the point of interest matters. If you have a very thick block of copper, then heat dissipation
is not at all a problem. So apart from specimen material, specimen volume also plays a role.
And we have always been saying, whenever you do a strain gauge installation, we must provide
a proper coating, so that changes in weather does not affect your installation. That is
good from one point of view - it prevents moisture absorption. From heat dissipation
point of view, what is the type of weathering is used, and what is it thickness also plays
a role. Because if I put a very thick weathering coat, you are not allowing heat to dissipate.
On the other hand, if I have a high velocity of the air flowing over the installation,
it is well and good.
So the manufacturer also looks at it differently. They recommend what is the allowable power
density; that is the way they look at it. So you have a power density defined as P by
A. P is the power to be dissipated, that you can also calculate from I square R loss, and
A is the grid area. See, later we will also go and see selection
of strain gauge, where will see a variety of patterns, and you will find, you get gauges
of different grid area. Why such grids are available, you will know from charts that
say for a given application, and a given power density, what kind of grid patterns I can
select. So I need to look at and approach the problem scientifically; so I have a parameter
for a given type of specimen material and for the thickness what is mention - this is
the power density that it can safely operate. And what you find here is, if I have a heavy
aluminum or copper section, the power density permissible in watts per millimeter squared
ranges from 0.008 to 0.016. And when I go for heavy steel sections, the power density
value reduces; and when I go for thin steel sections, it reduces further. And when I go
for poor conductors like fiber glass, glass, ceramics, unfilled plastics the power density
permissible is almost close to 0. It is very, very small - so you need to have very efficient
heat dissipation. And that is the reason I said, if you have to work on composites, which
are becoming very important structural members, you need to go for higher strain gauge resistances.
And mind you, when you go for higher strain gauge resistances, they are also very expensive
and not cheap. Because we have already looked at making a small strain gauge with even 100
ohms, you needed a longer wire. So if I want to have 1000 ohms at the same place, unless
I improve my technology, is not possible. And when improvement technology also demands
high cost. So if you want to go for sophisticated applications, you need to go in for higher
cost; has no other way that is available for you.
So this is what you have to look at: allowable power densities are strongly related to the
specimen. That is what this table essentially brings out. So in a strain gauge installation,
I said strain gauge as the system consisting of grid alloy, carrier, and adhesive - now
you find from the heat dissipation point of view, even the specimen material decrease.
And the manufacturer supplies you with the such complicated graphs. I will try to explain
it with the very simple fashion. So, on the x-axis, you have a grid area. I will also
enlarge it a little while later. First on the x-axis, note that you have a grid area;
on the y axis, you have the bridge excitation voltage. So my idea is to find out the excitation
voltage, so that I satisfy the power density requirement. And what you have here is, on
the graph you find slanted lines - these lines indicate different values of power density.
So if you look at it zoom - so what I find here is, I have a line for 0.01 watts per
inch squared, or it is 0.016 kilowatt per meter square, and the power density increases
in this fashion. So if I know for a particular specimen material, only a particular power
density is permitted, then this tells me what kind of great patterns which I can choose.
I suppose you are able to see this letters, is have not able to enlarge it, and what you
find here as 250AE, 250AF - they indicate, first is the length of the gauge length, expressed
in mills, and AE, AF, DA, EA - all this pertain to particular strain gauge manufacturers classification
of the grid pattern. You have so many grid patterns - you know they shown out many different
grid patterns, and for each one of the manufacturer will provide you a graph like this, for you
to select the suitable grid pattern, and also decide on the selection of bridge excitation
voltage.
And if you look at the graph, you have a cluster of gauge grid identification here. You have
another cluster of gauge grid identification here. This is essentially grid area. You could
have a wider grid, you could have a narrow grid - you have different types of pattern.
You know your measurement application you decide whether you need a wide grid, or narrow
grid - all that decisions you will have to take
And if you also look at this graph, is available for 120 ohms - and this is the particular
graph for 120 ohm strain gauges. Suppose I go for a 350-ohm strain gauges, these power
density graphs get shifted. So, that means, I can offer to apply a higher voltage for
the same power density if I use a higher resistance of the strain gauge. And you have also have
another graph for 1000 ohms, this is just to give you an idea such selection graphs
are available from the manufacturer.
So how I go about and select the bridge voltage? If we look at most common strain indicators,
use bridge voltage between 3 to 5 volts. Small gauges mounted on a poor heat sink result
in lower allowable bridge voltage. So there is the reason, when we had a discussion on
selection of gauge length, we saw if the strain is varying linearly. Length of the gauge length
do not matter in interpreting the strain at the center of the strain gauge; only when
there is the non-linear variation, when I need to worry about selecting a suitable gauge
length. I will also caution, when you select a smaller gauge length - is expensive, difficult
to make - and in addition, you need to worry about what is the bridge excitation voltage
that you can select; and also make special provisions for heat dissipation. You must
allow a stream of air for you to cool the strain gauge installations or some such special
attention you need to pay. And suppose you are unable to improve your
heat dissipation so the external means, you can at least think of using a higher resistance
gauge, or a gauge with the larger grid area. This is the kind of selection compromise:
see if I have a larger grid area, then I am deviating from idealizing measurement of strain
at a point. I am measuring it only through area. This is possible only then the strain
variations are small as a function of distances. So selection compromises always exist - without
compromises, you will not be able to handle a problem.
Now we have talked about influences of temperature. In some form, you should also look at what
is the sensitivity of the gauged temperature - what happens when the temperature … The
strain sensitivity S A of the metal alloy used for the grid changes. We will have to
see how does it change - that is the question. And for simplification, for a change of plus
or minus 10 degree centigrade, the variation of S A is usually neglected. And it is obvious,
depending on the coefficient of expansion; when the temperature changes, the gauge grid
either elongates or contracts; specimen either elongates or contracts, depending on the delta
T. And you also find, the resistance of the gauge changes, because we have earlier written,
the change of resistance original resistance has S T in to epsilon. On similar lines, you
write the expression S T into delta T. And you label S T as, sensitivity of gauge to
temperature. S T is the gauge factor which is used in interpretation of change in resistance
to axial strain. When I bring in effect of temperature, I bring in another parameter
called S T, which has to be evaluated again experimental.
How does this S A change as the function of temperature?
And what you find is, fortunately it is the linear graph, for the popular strain gauge
material like advance karma, as well as high temperature applications like nichrome, armour
D, as well as the platinum constraint type of strain gauge alloy. Only for isoelastic,
it is non-linear. So if it is linear, it is good enough. So you just make to note, that
advance and karma it is varying linearly, that is what you need to worry about, itself
variation is linear; fortunately, it is linear. So we can do some kind of a correction in
that.
So what you find in quantitative terms is, change in the strain sensitivity of the conductor
as the function of change in temperature is 0.735 percent per 100 degree Fahrenheit for
advance. It is minus 0.95 percent per 100 degree Fahrenheit for karma. So you have this
data: it is possible because strain gauge is constructed based on a conductor, so I
need to know the conductor property. Then I need to look at, when I make it as the loop,
how does this changes. So what we will look at is, handling temperature information and
segregating the change in resistance you to stress applied, and temperature change is
the most challenging aspect in strain gauge instrumentation.
So in today’s class, what we saw was we will looked at how to use ceramic cements
and what is the kind of strain gauge that you need to use for high temperature application.
Then we moved on to performance analysis of the strain gauge system. I said you need to
worry about deviation from linearity, hysteresis, as well as zero shift. And we found the constitutions
forming a strain gauge influence these aspects. We saw selection of the carrier influences
the linearity; selection of the alloy as well as the carrier, and an appropriate adhesive
can improve stability for a very long duration - for selection is very important. Then we
moved on to another subtle issue - how does temperature changes occur.
One of the subtle changes is current flowing through the strain gauge itself can heat it
up, and you find the heat dissipation is the function of the specimen material. Not only
the strain gauge system, you should also consider on which material we want to operate, which
decides selection of the bridge voltage also indirectly decides the selection of the resistance
of the strain gauge alloy, and also the type of grid - whether you want to go for a wider
grid or smaller grid or whether you want to go for stack rows is possible or whether you
need to go for un stack row sets only - possible for this kind of heat dissipation. All those
decisions are dictated by the heat dissipation capacity of the specimen material. So, this
takes you a step ahead on how to do effective strain gauge instrumentation.