Frequently Asked Questions

I need a special, custom, or modified extensometer.  Can you help?

Yes, we have over 15 years of experience in designing extensometers.  We have designed many custom or one-off extensometers. Please call us to discuss your needs.

Can Reliant extensometers be left on through specimen failure?

Yes, Reliant extensometers are designed for use through specimen failure.   However, testing hard / high strength materials will cause knife edges to wear out faster.  A spare set of knife edges is included with each unit, but knife edges should be inspected regularly and spare sets may be needed.

One way limit wear-and-tear to your extensometer is as follows:   Using a lower measuring range extensometer (5 to 20 % strain), run your test until a certain strain is reached, pause the test, remove the extensometer, and resume the test using the actuator or crosshead travel to obtain the rest of the test data to specimen failure.  This procedure allows approximate measurement of elongation to failure (the data at elongation to failure is not normally critical).  Using this procedure will reduce the amount of wear and chance of damage to your extensometer's knife edges.   However, not all test controls allow you to pause a test; please check your system's capability.

Will the extensometer be compatible with my existing electronics?

All of Reliant's extensometers are strain gage based.  They may be connected to most brands of materials testing controls. If your machine includes a strain-channel for sensor input, we can supply your extensometer with the proper connector to directly plug-in to your controls.   We stock interface connectors for most brands of test machines including Instron, MTS, Admet, & United.

If you have an older control designed for LVDT extensometers or you are using a chart recorder / data acquisition board to acquire test data, we can provide a stand-alone signal conditioner to attain the required high level signal.  

What electronics are needed?

All of our extensometers are strain gage based and utilize a full Wheatstone bridge design. As such, they will require some sort of signal conditioner (excitation supply / amplifier).  Most modern test controls have the signal conditioning electronics built-in or have space for an optional signal conditioning card. For older machines / controls, Reliant can proved a stand alone signal conditioner / extensometer system to allow you to use a chart recorder / data acquisition card to acquire test data.

How do I decide what measuring range I need?

Selecting an extensometer with the proper measuring range is a trade-off of sorts.  In general, the extensometer's measuring range should match the amount of specimen elongation your are seeking data for.  For testing modulus of elasticity or yield strength, an extensometer with a smaller measuring range will give the best results.  However, an extensometer with insufficient measuring range may prevent measurement of larger elongations.

For example: when testing ductile materials (most metals and plastics), tensile tests are often run to specimen failure to obtain the whole stress-strain curve.   If your  extensometer has a high measuring range (50 or 100 % strain), the accuracy of the measurements at low strain levels will be somewhat degraded (yield strength and modulus of elasticity often occur in the range of 0.1 to 2 % strain). 

One way to obtain data for the full stress / strain curve with a low measuring range extensometer (5 to 20 % strain) is as follows:  Run the test until a certain strain is reached, pause the test, remove the extensometer, and resume the test using the actuator or crosshead travel to obtain the rest of the test data to specimen failure.  This procedure allows approximate measurement of elongation to failure (the data at elongation to failure is not normally critical) with a low measuring range extensometer.  Using this procedure will reduce the amount of wear and chance of damage to your extensometer's knife edges.   However, not all test controls allow you to pause a test; please check your system's capability.

For those using a high measuring range extensometer, it is possible to get more accurate low strain measurements by adjusting the electronics during calibration.  Since the data at elongation to failure is not normally critical, the gain of the electronics can be adjusted to maximize the accuracy at the low measuring end. The trade-off is more error at the end of the measurement range where the accuracy of the data is less critical.

In general, Reliant's extensometers will meet the high accuracy requirements in today’s standards, such as ASTM class B-1.  Standards like ASTM E83 assure reasonably accurate measurements at the low end of the range by requiring some levels of accuracy to be expressed in percent of reading, not percent of the full scale range.  

Why can't I use the crosshead displacement to measure strain?

The crosshead deflection is the total deflection (specimen, grips, test frame, etc.) seen during a test and does not accurately measure the strain in a defined region of a test sample. Strain is a unit less measurement of the change in length divided by the initial length (gage length) in a defined region of the sample. An extensometer is required to measure the change in length over this defined area.

Do you repair other brand extensometers?

We can do electrical repairs on most any strain gage based extensometer.  We have experience in repairing MTS, Instron, United Calibrations, Shimadzu, Epsilon, etc.   Please note: we do not repair LVDT based or mechanical extensometers at this time.   Please contact us for a free inspection and quote of your extensometer repair.

I have an X-brand extensometer and I need to interface to a Y-brand machine.  Can you help me?

We have experience in interfacing to most all electronics.  We can install the required interface connector on your extensometer or build a custom adapter cable for you.

I have an X-brand extensometer rated for room temperature.   Can you convert it for use at low / elevated temperatures?

Yes, we can replace strain gages / cables and apply the coatings / protection needed to convert the temperature range of your extensometer.