Extensometers and Settlement Gauges




Rod extensometers are used in geotechnical monitoring to monitor and measure with precision movements of one or more surface points, with respect to points considered fixed and located at different depths in the rock. (bedding, subsidence and deformation) Reference points are formed by special anchors, fixed in boreholes at the desired depth through cementing or by using special devices. Each measuring rod is linked to the relevant anchoring point which connects to the reference head. These rods are inserted in a protective covering which insulates them from the surrounding soil or filling grout and ensures free sliding. The rods, free to slide inside the covering, allow measurement of the relative movements between the anchoring point and the reference head installed on the surface. Measurement is performed manually by means of a gauge, analog or digital or by means of automatic displacement sensors (potentiometers, LVDT or vibrating wire). Measurements are made absolute by the certainty by the stability of the reference point or by measuring the instrument head using another method.

Different types of rod extensometers are available:

  • Single-point or multi-point, up to six measuring points;
  • With vibrating wire displacement transducer or potentiometer
  • With manual reading, or with manual and automatic reading
  • With stainless steel rods or fiberglass (Invar rods on request)
  • With standard anchors in concrete or specific to requirements

The instrument can be read with our portable unit DEC3000 or with our automatic acquisition unit DAC3000.



Rod extensometers are used for monitoring small displacements in rock or soil where a high degree of precision is necessary such as: the shifting and settling of foundations, the relaxation or yielding of rock around tunnels, shafts, caves.
Typical applications include:

  • Monitoring of movement or settlement in foundations
  • Monitoring of tunnels, shafts, caves etc
  • Monitoring of natural slopes, quarries and mining operations
  • Monitoring of deformation of retaining walls, bridge pillars and shoulders
  • Monitoring of dam foundations, intake towers and shoulders


Features and Benefits:

High sensitivity and precision

Strength of materials

On site assembly

Easy installation

Automation of measurement and configuration for remote readings

Verification of automatic measurements using manual readings without removal of the sensor

Length and type of rods customizable to specific needs.

Monitors up to six measuring points in one borehole

Reliability over time

Can be used with vibrating wire displacement transducers, potentiometers or LVDTs

Measuring principle:

The rigid rods of the multi-point extensometer are anchored at one end in specific locations in the soil or rock and slide in protective guide tubes , being free to move in one direction only.

The free ends of the rods are correlated to the instrument head (reference head) fixed at the
surface and form the different measuring points. Distances between the free end of the rods and the reference head ,measured over time, provide the movements of the various anchoring points relative to the head.

Movements are measured manually using a caliper or a dial gauge, or automatically through displacement transducers.

The displacement transducers, fixed on the instrument reference head, can be LVDT, potentiometer or vibrating wire. Depending on the ground movements expected , sensors with different ranges can be chosen.

Reading of the potentiometric transducers can be performed manually with our hand-held read-out units or our portable datalogger DEC 3000; or with our automated datalogger CUM3000

Rod extensometers can be integrated into automatic monitoring systems with real-time monitoring of phenomena and managed with local and remote real-time alarms
In addition, versions with displacement transducers retain the facility to perform manual readings without the need to remove the sensors.

Stainless steel and Invar rods are supplied in lengths of 2 or 3 meters, linkable with threaded pins.
Guide tubes may be made of flexible, single piece nylon or of rigid linkable piping (length 2-3m or on request).

Fiberglass rods are supplied ready assembled in the workshop, to the desired length and complete with anchors and nylon guide tubing.

Stainless steel or Invar steel rods, complete with flexible or rigid protective pipes can be supplied on request.

Rigid pipes can be supplied with ball bushings or Teflon sleeves.
Standard anchors are suitable for cementing into rock or soil
For particular soil conditions or specific installation requirements, special anchors can be made on request.
The reference head is made of stainless steel complete with protective cap. this facility allows control and reliability of electrical measurement and continued readings in the case of maintenance to or replacement of the sensor.

Fiberglass rods are supplied ready assembled from the workshop, of the desired length and complete with anchors and protective sheath with nylon guide tube.


Technical Specifications:

Version Glass Fiber Stainless Steel Invar Wire in stainless steel
Diameter 7mm 8mm 8mm 3mm
Weight/meter 0,09 Kg/m 0,4 Kg/m 0,41 Kg/m
Young’s Modulus 20 GPa 200 GPa 140 GPa 200 GPa
Coefficient of thermal expansion 3 ppm/°C 17 ppm/°C 1 ppm/°C 17 ppm/°C
Junction Continuous


Threaded Bars M/F


Threaded Bars M/F

Protective Sheath

nylon Ø 12 mm

tubo PVC da 1/2”

In rods 3M long In rods 3M long Nylon or PVC tube
Anchorages Galvanized steel L=500 mm Galvanized steel L=500 mm Galvanized steel L=500 mm Galvanized steel L=500 mm
Reference head Stainless steel Stainless steel Stainless steel Stainless steel


Vibrating Wire Transducer:

Technology Vibrating Wire
Temperature Sensor On board
Range 5 ÷ 50 mm
Accuracy ± 0,2% f.s.         (Including linearity, hysteresis and repeatability)
Linearity <±0,02%f.s.
Resolution <0,02% f.s.
Frequency Range 500 Hz ÷ 1000 Hz
Operating temperature -20°C÷
Power Supply From Datalogger
Material Stainless Steel
Inner Rod Stainless Steel
Anchor Types Dowels, threaded bars, fixtures
Protection IP67 or IP68 up to 10 atm
Signal Cable 2 x 0,5 – 3x 0,5 with thermistor on board
Max Distance to Datalogger 1000 mt


Potentiometer Transducer:

Technology Linear Potentiometer
Temperature Sensor On board
Range 5 ÷ 50 mm
Repeatability 0,01mm
Linearity ±0,1 % f.s.
Resolution Dependent on datalogger
Power Supply 9÷36 V
Material Stainless Steel
Inner Rod Stainless Steel
Anchor Types Dowels, threaded bars, fixtures
Protection IP67  (IP68 up to 10 atm  on request)
Signal Cable 2 x 0,5 – 3x 0,5 with thermistor on board
Max Distance to Datalogger 1000 mt



MODEL Caliper  Dial Gauge
Range 200mm 50mm
Resolution ± 0,1 mm ± 0,01mm
Accuracy ± 0,2 mm ± 0,02mm



Caliper Device for the manual reading of rod extensometer
Dial Gauge Device for the manual reading of rod extensometer
Junction Boxes Available in different models for the connection to different instruments
Multiwire Cable Available with different conductors for the connection of different sensors to one cable
DEC 5 Portable Readout Unit
DEC 3000 Portable Datalogger
CUM 3000 Multichannel Datalogger
MUX Multiplexer for the connection of different sensors to Datalogger

Technical Assistance:

If you have any requests or questions about our instruments or if you have special needs that require different solutions from the standard, please contact us. Our team will provide all the necessary information and will be very happy to work with you to study, develop and customize instruments and solutions suitable for your specific needs.

All information in our datasheet is subject to change without prior notice.

Please check the datasheet/details carefully and contact Pizzi Instruments for further information.