An extensometer is an instrument that measures the strain on material samples during material testing e.g. tensile tests. In principle there are two types of extensometers - contacting and non-contacting ones. Contacting measurement can be performed by means of a clip-on extensometer; such an instrument has at least two edges that are attached mechanically to a specimen. Stretching a specimen results in a longer distance between the edges corresponding with the change in length of the specimen.
For non-contacting measurement analog or digital optical extensometers are used. For measuring strain on material samples the specimens often are provided with black-and-white marks. The sensors within the extensometer detect the motion of the marks and thus the change in length during a tensile test. There are extensometers, which are able to measure very fast strain (>100 m/s), even if the material sample temperature is very high (up to 3000° C).
During tensile tests non-contacting measuring devices are advantageous; they often can be set up at a certain distance to the specimen in order to keep flying fragments of the specimen from damaging the measuring instrument. Therefore optical extensometers are also suitable for measurements during destructive material testing.
The H.-D. Rudolph GmbH offers various types of optical extensometers:
- Extensometer 200XR for very fast tests of up to 500 kHz
- CMOS Line Scan Sensor ZS64A5K for high resolution of 1:64000 and 4673 measurements per second
- Line Scan Sensor ZS16A respectively the faster version ZS16AHS for high resolution of 1:16000 at high stability
- Extensometer ZS32 respectively ZS32HS with a resolution of 1:32000
Extensometer 200XR
Strain Analysis
The electro-optical Extensometer Model 200XR contactlessly measures the motion of two black-and-white edges (targets) on a sample. The analog output signal is proportional to the strain. The frequency range of Model 200XR amounts to 0 – 250 kHz. The integrated viewer and the two liquid crystal displays simplify the performance of the adjustments required for the setup of the instrument; the viewer also allows observing the black-and-white edges on the sample while measuring takes place. Lens units with different measuring ranges of 1 mm - 500 mm can be mounted to Model 200XR by means of a flange. The calibration of the lens units results in an output voltage Δl of ±10V for the range of strain.
There is the option of delivering the 200XR with a switch to toggle between the two measuring axes; this allows using the instrument also as Biaxial Extensometer 200XR in order to measure strain in either vertical or horizontal direction.
The standard gauge length lo is 75 mm. A continuously adjustable gauge length of 1 mm up to 125 mm can be established by gauge length adapters mounted to the lens units.
CMOS Line Scan Sensor ZS64A5K
The ZS64A5K is a CMOS line scan sensor with a very high resolution used for non-contact dimensional measurement. By means of a lens the object to be measured is imaged to the linear CMOS array in the sensor. The lens determines the measuring range. Standard lenses can cover measuring ranges from 1 mm to 5000 mm.
Characteristics of the ZS64A5K:
- High resolution of 1:64000
- Measuring range 5 mm – 5000 mm
- High sensitivity for shortest exposure times
- Scan rate 4673/s
- Narrow scanning width
- Standard version: Detection of two edge positions, light/dark or dark/light
- Measuring values: Edge A, Edge B, B-A or (A+B)/2
- Optional version: Detection of max. eight edge positions
- Analog, calibrated live measuring values
CCD Line Scan Sensor ZS16A and ZS16AHS
Non-contact Dimensional Measurement
The ZS16A is a CCD line scan sensor with very high resolution used for non-contact dimensional measurement. By means of a lens the object to be measured is imaged to the linear CCD array in the ZS16A. The lens determines the measuring range. Standard lenses can cover measuring ranges from 1 mm to 2000 mm.
Characteristics of the ZS16A:
- High resolution 1:16000 (interpolated)
- Measuring ranges 1 mm - 2000 mm
- Measuring distances 20 mm - 200 m
- High sensitivity for shortest exposure times
- Scan rate up to 1000/s, optionally 4673/s with the ZS16AHS
- Narrow scanning width
- Analog output
- The ZS16A is designed to be operated with 18 – 36 V, DC
Digital Extensometer ZS 128
Strain Analysis
With 4673 measurements per second and a resolution of 1:128000 the digital Extensometer ZS 128 electro-optically measures strain on samples. The digital sensors guarantee high stability and maintenancefree operation. The immediate delivery of calibrated values takes place during dynamic as well as endurance tests. The ZS 128 is able to perform measurements of strain on material hot up to 3000° C.
Characteristics ZS 128:
- Measuring ranges: 2 - 1000 mm
- Measuring distances: 40 mm - 10 m
- Resolution: 0.0016 %
- Scan rate: 4673/s