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Dear Sir,

we are using a H5KS in combination with extensometer H500L, on occasion of an interlaboratory cross check we found out that in our rubber testing results we find always too low modulus300% results...elongation results are too high which is in line with the too low modulus... What could be the reason ? We are assuming that this has something to do with machine settings...is it possible to apply a preforce-threshold, before measuring starts... I am sorry to ask you this, but I also want to point out that we only got an manual in english language which is not really helpful...not only because of our bad english knowledge ;-). Thanks for your answer which is highly appreciated !

ANSWER

Thank you for your question.

The problem you are experiencing is very unusual. The laser extensometer is auitable for medium to high elongations and is ideal for rubber testing. It is both accurate and reliable. It has been manufactured by Tinius Olsen/Hounsfield now for well over 20 years and has hundreds of users so it is well established and well proven in the market. You should be getting accuracies better than 1% of reading, usually better than 0.5%.

I assume you are using the mounting bracket supplied with the extensometer? This sets the extensometer the correct distance from the test sample and also sets the alignment. If you are not using the bracket and it is closer or further away from the test sample, you may well get errors..

It is very easy to run a simple check. You can do this by putting two reflective marker strips on a piece of stiff card 100mm apart centre to centre. Clamp one end in the top jaw and the other in the bottom jaw. Cut the card with scissors between the marks and recheck they are 100mm apart. Zero the crosshead encoder on the machine, drive the crosshead up 100mm exactly and read the percentage elongation derived from the laser extensometer. It should read 100%. There is also a procedure towards the end of the laser extensometer manual which details a procedure to veriofy and set the alignment of the device for very high extensions. tinius Olsen can also supply a calibration bar for the laser with 25mm and 125mm gauge marks. This is for mm versions of the extensometer. Please consult your Tinius Olsen Distributor for further information.

Please be aware that the laser is a digital device and is very accurate. It may well be the other measurement that is wrong.

if you are still experienciing problems, please consult our free helpdesk. These are based in the UK, USA and India. The Uk number is 01737 765001.

Tinius Olsen supplies English versions of instruction manuals but many of our Distributors do translate them into their own language so it is worth checking with your Distributor if one is available in your language.

I hope this helps,

regards,

David