1. Why does IBIS 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. LVDTs 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 IBIS, the design of the head fetures 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 IBIS, this happens in real-time in the electronics, and is not simulated digitally. 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 some 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 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 with feed forward control has been designed to eliminate the possibility of deleterious overshoot, especially as the stiffness of the system chnages when the indenter makes contact with the surface. 

3. What's the difference between a frame-reference and a surface-reference nanoindenter?

Nanoindentation requires the depth of penetration into the surface of the specimen to be measured. Thus, the zero point, or reference, for this measurement has to be the free, undeformed surface of the specimen. The majority of nanoindentation instruments are frame reference devices where the reference for the depth measurement sensor is the frame of the instrument. In most instruments, the absolute position of the specimen surface is found by the reading on the depth sensor when the force sensor makes contact with the surface at the initial contact force. The inevitable small penetration at this force is then calculated from Hertzian fitting to the load displacement curve at the contact. Many years experience has shown this to be a very reliable measurement of the depth reference point. In a surface reference device, a separate probe makes contact with the surface and the depth sensor reference for the actual indenter is taken from the position of this second probe. This is differential measurement. Proponents of this method have used various mechanisms and probes over the years to achieve some uniformity of procedure. Despite the seeming advantages, the most unfortunate aspect of the method is that relies on  the contact of the reference probe to be clean, solid, and repeatable for each and every indentation. On a nanometre scale, surfaces are seldom of this nature, and contact involves the deformation of asperities, surface films, and plastic deformation and creep. Some strategies have been developed to attempt to overcome these issues. If you are considering such an instrument, you should ask about the mechanisms for performing scratch testing, creep in soft materials, sloping specimens, specimens of different height, rough specimens, very small specimens or test areas, and so on.  

4. Is ease of use important?

Image you had to do this each time you performed a nanoindentation test? 1. adjust the capacitance bridge circuit for maximum signal, 2. calibrate the depth sensor, 3. calibrate the zero balance, 4. manually set the working distance - and then, every month or so, calibrate the force actuator. Each time you do the above, you risk breaking the ceramic indenter rod.

In contract to the above, IBIS has separate, and dedicated force and displacements sensors which are separately calibrated against international standards of mass and displacement and do not require periodic recalibration or adjustments. The titanium indenter shaft passes through the centre of the LVDT sensors and so there are no contacting parts. The indenter shaft can withstand rough handling without damage. The dedicated force sensor offers automatic collision detection for safety. There are no daily or weekly adjustments required. Changing the indenter does not require special precautions. IBIS has an automated, motorized z axis approach that does not require user intevention for setting the working distance. With IBIS, you test and go - no fussing around.

5. 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. In one case, the manufacturer of a competitor instrument calibrates the depth sensor against the encoder output of the sample stage movement! 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.

6. 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. With Fischer-Cripps Laboratories, our representatives and customers work together and 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 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 and USA markets at a competitive price.

7. 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).

8. 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.

9. 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 because 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.