### Temperature correction values for rod extensometers

**Figure 1. Rod extensometer**

**1. Introduction**

The single rod extensometer employs a rod, anchored at one end of a drillhole, passing into a reference tube fixed in the drillhole collar (see Figure1.). Relative movement between the end anchor and the reference tube is measured with either a dial depth gauge or a vibrating wire displacement transducer inserted through the reference tube and registering on to the free end of the rod. Due to the materials used during the manufacturing of the both the rods and the vibrating wire displacement transducers there are individual temperature correction values for the transducers and the extensometer rods.

**2. Temperature correction values**

Below you can find the temperature correction values for the vibrating wire displacement transducers as well as the values for the stainless steel extensometer rods and the fibreglass extensometer rods.

- For the displacement transducers:

The working elements are made primarily of steel and stainless steel and are affected by changing temperature to a certain predictable degree. In case of large temperature changes application of temperature correction will improve the accuracy of the measurements. The approximate temperature effect on the gauge is -0.02mm per degree Celsius. Hence for a temperature increase of 10°C a crackmeter will indicate:

-0.02 x 10 = -0.2mm

In this case, the value is then subtracted from the mm reading taken from the resultant vibrating wire rod extensometer reading. A fall in temperature will result in a positive change in linear measurement which can be corrected accordingly.

- For the Extensometer rods:

There are two types of extensometer rods that we provide with our extensometer systems, these are stainless steel and fibreglass

If you are using the stainless steel rods the formula is:

Temperature expansion coefficient 17.5ppm (metric)

dl = L0 (E^-6 x α) (t1 - t0)

where

dl = change in length (m, inches)

L0 = initial length (m, inches)

α = temperature expansion coefficient

t0 = initial temperature (oC)

t1 = final temperature (oC)

If you are using fibreglass rods the formula is:

Temperature expansion coefficient of 3ppm (metric)

dl = L0 (E^-6 x α) (t1 - t0)

where

dl = change in length (m, inches)

L0 = initial length (m, inches)

α = temperature expansion coefficient

t0 = initial temperature (oC)

t1 = final temperature (oC)

If this has not solved your issue please submit a ticket through the support site.

If you are using the stainless steel rods the formula is:

Temperature expansion coefficient 17.5ppm (metric)

dl = L0 (E^-6 x α) (t1 - t0)

where

dl = change in length (m, inches)

L0 = initial length (m, inches)

α = temperature expansion coefficient

t0 = initial temperature (oC)

t1 = final temperature (oC)

If you are using fibreglass rods the formula is:

Temperature expansion coefficient of 3ppm (metric)

dl = L0 (E^-6 x α) (t1 - t0)

where

dl = change in length (m, inches)

L0 = initial length (m, inches)

α = temperature expansion coefficient

t0 = initial temperature (oC)

t1 = final temperature (oC)

If this has not solved your issue please submit a ticket through the support site.