A double-puncture technique for improving the accuracy of puncture tensiometer measurements

Abstract

Measurements taken with a puncture tensiometer are biased due to the small positive pressure exerted on the system when the syringe needle is inserted into the air space at the top of the tensiometer. An equation based on Boyle's Law, relating two successive measurements from puncture tensiometers to the initial tension, was developed to correct this problem. The initial tension, T₀, inside the puncture tensiometer can be calculated from T²₁/ T₂ where T is the tension inside the puncture tensiometer and the subscripts 1 and 2 refer to the first and second readings taken with the puncture tensiometer meter.

Laboratory testing at tensions of 5, 10, 20 and 40 kPa showed that average results from this double-puncture technique were within 0.2 kPa of the actual tension. All results using this technique were accurate to 6%. In contrast, the average tension calculated from the single-puncture tensiometer readings underestimated the actual tension by up to 2.3 kPa and the maximum errors were approximately 10%. Use of the double-puncture technique will improve puncture tensiometer measurements in the field without the need to wait for re-equilibration of the pressure or application of calibration equations.