Natural Gas Measurement Basics: Gauge-Line Error from Pulsation
Common industry practice is to install gauge lines (meter tubing) of less than 18 inches between the tap valves and differential pressure transmitter on an orifice meter. This minimizes the potential for multiple sources of measurement error including meter freeze, liquids, and, perhaps even more importantly, gauge-line error due to pulsation.
Gauge-line error associated with compressor-generated pulsation occurs when a quarter-wave resonance occurs in the meter tubing. According to well respected and widely accepted studies, most pulsation present in orifice meters has wave lengths longer than 72 inches. Therefore, if the gauge lines are less than 18 inches
(one-quarter of 72), the likelihood of gauge-line error should be effectively eliminated.
You may click here
for basic field procedures to detect the presence of gauge-line error. Please note that this is not a method to detect measurement inaccuracies associated with square-root error, which always causes an orifice meter to read high and can be very difficult to detect. For a more comprehensive review of the methods to detect and eliminate errors associated with compressor-generated pulsation, you're invited to register for one of our Lunch & Learn classes scheduled during the remainder of 2011. The full schedule is available on our website at http://www.coastalflow.com/Training/Schedule/
, along with a registration form in PDF format, or you may contact our offices at 800-231-9741 for more details.