Further Studies of the Accuracy of Clamp-on Transit-Time Ultrasonic Flowmeters for Liquids

The higher value of uncertainty in the flow measurement signal from transit-time clamp-on ultrasonic flowmeters (USFMs) compared with transit-time spool-piece USFMs is due to several factors, some of which have been considered in this paper. However, the main focus of this paper has been on the effect of separation distance between the transducers on the flowmeter output signal. The sources of experimental error that might affect the validity of the data obtained for the transducer separation are examined, and then, use of ray-tracing and finite-difference models is made to examine this relationship theoretically.

I. Introduction

Ultrasonic flowmeters (USFMs) are one of the fastest growing technologies within the general field of instruments for process monitoring, control, and measurement. In 2005, they captured approximately 10% of the sales volume for all types of flowmeters [1]. These meters are available as a spool-piece meter or as a clamp-on meter for liquids and gases. The transit-time spool-piece USFM has a lower uncertainty than the transit-time clamp-on USFM [2]. This paper will consider some reasons for this. Reference [3] presented initial results of a study on the clamp-on ultrasonic transit-time meter. This paper gives a fuller treatment, including further test results that demonstrate the repeatability of data.