Temperature correction factors for vibrating wire piezometers


1. Introduction
This guide details the steps taken in the design of Soil Instrument Piezometers to keep temperature effects to a minimum and the alternatives offered for environments in which there is rapid temperature change.

2. Temperature Correction
Soil Instruments manufactured vibrating wire Piezometers incorporate compensation for the effects of changes in temperature, this negates the need for correction factors in most installations.

As the temperature increases the stainless steel internal body of the Piezometer expands at a greater rate than the carbon steel vibrating wire. This would normally cause an increase in the tension of the wire and a change in the readings from the Piezometer. To compensate for this effect we incorporate a compensation material into the internal body, this material has a lower rate of expansion than the stainless steel. By carefully proportioning the ratio of stainless steel to the compensation material we are able to virtually eliminate the effect of temperature change on the Piezometer.

Typically our Piezometers have an effect of temperature change of less than 0.025% full scale/°C
Most Piezometers when installed will be subjected to small and gradual temperature changes that do not require correction values to be applied to the readings.

For situations where large temperature changes are expected we can provide individual compensation factors providing these are requested at the time of order.
 

Tip: Rapid changes in temperature cause the inner body to expand earlier than the wire causing an increase in the readings, this will reduce once the temperature of both the wire and the body equalise.