Here we answer your questions about IBIS nanoindenters and associated technology.
1. Why does IBIS (and UMIS) use LVDT sensors?
LVDT sensors are “linear variable differential transformers” and are
essentially inductance displacement sensors. They are inherently
linear, and have sub-nanometre resolution. Their performance is very
similar to the capacitance sensors used by other manufacturers with
one very important exception. LVDT’s are very robust. A capacitive
sensor consists of two, and sometimes three, parallel
plates. Unfortunately, the plates
have to be, by necessity, of very precise geometry, and be
positioned very close together. It is common to make these plates
from glass, and very common for the plates to break if the indenter
shaft, which is connected to the centre or moving plate, is pushed
or pulled unintentionally beyond the spacing (less than a mm) of the
plates. By contrast, the LVDT sensors used in IBIS are made from stainless steel
with a titanium shaft. The centre shaft passes right through the
device and so the IBIS nanoindentation
head can withstand significant abuse by untrained or inexperienced
operators without damage. Experience over 20 years has shown that
not one single repair to these sensors has been needed.
2. What's so good about a closed loop system?
In UMIS, and IBIS, the design of the head is quite different to
competitor instruments. In our instruments, there is a separate,
dedicated force sensor. The output from the force sensor is compared
to the user set-point and the difference is fed back to the pzt
actuator. This is a closed-loop system. in UMIS and IBIS, this
happens in real-time in the electronics, and is not simulated
digitally as in some competitor instruments that claim closed loop
operation. The advantage is that the
load is kept at the requested set point no matter what the indenter
is doing – this is particularly important for creep and scratch
testing. In standard nanoindentation tests, the closed loop system
ensures that repeated tests are performed at exactly the same load
increments in a precise and repeatable manner. In competitor
systems, the situation is quite different. One popular instrument
uses the current in the coil as a measure of the force applied to
the indenter. The problem with this system is that the current in
the coil is also used to deflect the indenter shaft support springs.
The current that is used for this deflection has to be subtracted
off in order to arrive at the residual current representing the
penetration resistance of the sample. Issues such as resistive
heating of the coil also affect the current draw. Such systems are
typically calibrated by hanging weights on the indenter shaft and
measuring the residual current. With UMIS and IBIS, the force sensor
produces a signal which is linearly proportional to the indenter
load 100%, there is nothing to subtract off. This closed loop system
has been a feature of UMIS (and now IBIS) since 1989 and the special
integrator loop in the circuitry has been designed to eliminate the
possibility of deleterious overshoot that can occur in less
well-designed systems.
3. What's the difference between a top-reference and a
surface-reference nanoindenter?
The majority of nanoindentation instruments are top-reference, or
frame-reference devices. This means that the depth sensor datum is
the frame of the instrument. This has some advantages and some
disadvantages. The main advantage is that the depth signal coming
frmo the sample is due to movement of the indenter within the sample
itself whereas in a surface-reference device, where the depth datum
is the specimen surface, any movement of the surface (such as
sinking in of the reference ring or ball) represents a moving
reference point. Top references devices have more room around the
indenter for ease of access to the indenter for changeover, are able
to accommodate specimens of different height, and by necessity, are
more robust in construction for better mechanical noise stability.
Proponents of surface reference devices often neglect to state that
their instruments cannot do scratch testing unless a separate head
is fitted, often claim superior resistance to the effects of thermal
drift - without realising that most of the effects of thermal drift
are due to changes in dimension of the contact point, not the
instrument or the indenter shaft, are not suitable for testing of
soft materials or undertaking creep experiments. The surface ring or
probe must make contacts with a reasonable force (to squash out any
asperities in surface roughness so as to attain a good contact) and
this leads to an undesirable uplift of the specimen surface in the
vicinity of the indentation and creep into the specimen during the
test. One must consider that with the 10 or so various
nanoindentation instruments on the market, only one or two have been
designed as surface reference devices.
4. How important is calibration?
Calibration is vital, and this is where UMIS and IBIS have another
significant advantage over other instruments. UMIS was developed at the
laboratory that is responsible for the dissemination of physical
standards in Australia. The force and depth sensors with UMIS and
IBIS are separately calibrated using an extremely short validation
path to primary standards of mass and length. Competitor instruments
typically use industrial standards that are somewhat removed from
the primary standard by comparison. Worse, such instruments, with a
combined force sensor/actuator, have difficulty in establishing the
true force applied to the indenter independent of the support spring
deflection and resistive heating. Deficiencies in these types of
calibrations are often masked by the indenter area function
determination and are not noticed by the user until a sample with
mechanical properties different to that used for the area function
is tested. With UMIS and IBIS, the force and depth sensors are
independently calibrated and many years experience shows that these
sensors will retain their calibration for over 15 years and longer.
5. What about customer service? Is there a local rep I can
call upon for help?
In some cases, there is local representative for UMIS and IBIS
instruments. Even though a competitor company may offer the services
of a local representative, and provide some semblance of peace of mind, in
reality, any enquiry of substance will be forwarded to head office
and your question will be passed through several hands before being
acted upon. With Fischer-Cripps Laboratories, our agents and
customers deal direct - direct with the engineer, the programmer or
the scientist. 95% of problems can be solved by email or direct
network connection. Often problems occur when the user of the
instrument is new and needs some advice.
Staff working on UMIS and IBIS have been with the program for many
years. We have a personal commitment to our customers, many of whom
have become good friends. You don't deal with a faceless
multinational company, but real people who are interested in your
problems and solutions. With a small dedicated team, our
business model is unusual compared to most instrument companies but
we are justly proud of our products which we know will last for many
years and provide quality, reliable data. Contrary to some belief,
we are able to sell direct into the EU market at a competitive
price.
6. Say I am interested, can you test a sample?
Generally yes. However, don't just send a sample without contacting
us first. We will want to know if the sample is suitable for
nanoindentation testing. Usually, a test is offered at no charge to
demonstrate the capability of the instrument. However, if the sample
is difficult, or a material that is not normally tested with this
type of instrument, a charge for time spent may be appropriate
(refunded against any future purchase).
7. How important is experience?
It's vital. It's easy for an instrument company to publish
specifications and have a product designed yesterday, but in
reality, there's a whole lot of detail needed to get it right in
nanoindentation. This attention to detail comes only at a cost - and
that is, with time. The IBIS instrument builds upon the 20 year
product history of UMIS so that it will work reliably and
consistently. Every instrument is individually calibrated, checked,
and verification tested against three standard specimens. The design
eliminates issues that plague competitor instruments. We've recently
seen some results taken with a fairly new-to-market competitor and
unfortunately, while there is a lot of marvellous gloss, the
unfortunate manufacturer, and their possible customer, have not
appreciated the instrumental issues involved in working at the nm
scale and their load-displacement curves are resplendent with subtle
but significant errors only visible to an experienced eye.
Unfortunately, these errors are easily masked by the indenter area
function until the customer comes to test a specimen with different
mechanical properties than that used for indenter calibration. With
UMIS and IBIS, real time
feedback, specially designed servo loop, low noise amplification,
rigid frame, consistent robust and powerful software, and 20 years
experience etc all add up
to an instrument that works well.
8. The price you show is incredibly competitive, is this
instrument high quality?
Yes. With IBIS, the aim has been to cut down on unnecessary frills,
gadgets and custom made items and concentrate on the core capability
of nanoindentation. We can offer this level of instrumentation at
this price becuase the development costs have been recouped during
the last 20 years of the product history. This instrument will provide results you can have confidence in. The three
year warranty, traceable calibration, the experience in instrument
design, the meticulous attention to detail, puts this instrument far
ahead of its competitors. We offer real value for money, not a
cut-down cheap product designed to attract your attention. IBIS is a
quality instrument that represents what nanoindentation should be -
reliable, accurate and affordable.
