Close icon Close icon

R-4 – Magnetic Probe Extensometer / Settlement




The R-4 is used to manually measure settlement or heave of soils at various depths, allowing the end user to create settlement/heave.


The R-4 consists of a magnetic reed switch mounted on a graduated tape and reel. The switch is activated by magnetic targets installed at different elevations along an access pipe in a borehole or within an embankment or fill.

The R-4 detects the position of the magnetic anchors outside the riser pipe when it is lowered down the access pipe. The probe is suspended by a single graduated tape that incorporates the electrical leads. The tape graduation is used to determine the probe’s precise position relative to the magnets. Comparison of these locations allows heave and settlement determination.

The magnetic anchors are available in three configurations: leaf spring anchor for borehole installation, plate anchor for embankment or fill installation and datum magnet that is fixed directly to the bottom section of access pipe. The leaf spring anchor can be pushed in place or lowered with the access pipe and released with an external draw wire.
The plate magnet is a plate with a central hole. The plate magnets are installed over the riser pipe and between the layers of placed fill, as the filling operation proceeds.

Telescoping couplings are used where deformations exceeding 1% are expected.TheR-4system is compatible with standard inclinometer casings. The use of a probe centralizer is recommended for repeatable readings.

Probe:  Stainless steel, 14.3 x 227mm
Cable:  Epoxy coated steel tape with medium density polyethylene jacket

Metric cables have 1mm graduations and imperial cable have 0.01ft graduation

Reel:  263 or 300mm in diameter depending on cable length
Battery:  The readout operates on with one 9-Volt alkaline cell.
Material: Magnet body in  PVC
Temperature range: -30°C to +80°C
Plate magnet dimensions: 200 x 200 x 9.5 mm standard, 300 x 300 x 9.5 mm optionnal
Access tube:   -Standard 1’’ pipe sch.80 flush-coupled PVC pipe (33mm)

(telescoping sections available if large settlementss are anticipated)

– 70mm or 85mm inclinometric casing

– optional 1.5” pipe sch.80 flush-coupled PVC pipe (48mm)

Model No. Casing
FR-1131A50300 33mm
FR-1131A50300C 48mm
FR-1131A50300A 70mm
FR-1131A50300B 85mm

Note: Probe with 100 or 300ft of cable also available

Readout Unit and Magnet model

READOUT UNIT (probe and reel)
Model No. Cable length Resolution
FR-1013E50100A 30m 1 mm
FR-1013E50100B 50m 1 mm
FR-1013E50100C 100m 1 mm
FR-1013E50100D 150m 1 mm




Model No. Min. borehole diameter Released

Outside diameter

FR-1131A50100 101 mm 222 mm 33 mm
FR-1131A50100C 101 mm 254 mm 48 mm
FR-1131A50100A 127 mm 279 mm 70 mm
FR-1131A50100B 152 mm 305 mm 85 mm


Model No. Casing
FR-1131A50200 33 mm
FR-1131A50200C 48 mm
FR-1131A50200A 70 mm
FR-1131A50200B 85 mm



Ordering Info

Please specify:

  • Borehole diameter and depth
  • Access tube model and length (For more information about 70 and 85 mm O.D. access tube, please refer to standard inclinometer casing data sheets)
  • Telescoping section
  • Anchor model number
  • Readout instrument model no.

Optional accessories:

  • Probe centralizer
  • Collar tape guide
Down arrow

Search Smartec