Panametrics PT878GC, Instruction Manual

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Chapter 10.
178 TransPort™ PT878GC User’s Manual
10.1.3 Flowcell Problems
Flowcell problems fall into two categories: gas problems and pipe problems. Read the following sections carefully to
determine if such problems exist.
10.1.3.1 Gas Problems
Most gas-related problems can be solved by proper design of the flowmeter installation and the proper choice of
transducer frequency. Contact Panametrics Sensing if you cannot solve a gas-related problem.
If the physical installation of the system meets the recommended specifications, it is possible that the gas itself may
be preventing accurate flow rate measurements. The gas being measured must meet the following requirements:
1. THE GAS MUST BE HOMOGENOUS, SINGLE-PHASE AND RELATIVELY CLEAN. Although a low level of entrained particles
may have little effect on the operation of the TransPort, excessive amounts of solid or liquid particles will absorb
or disperse the ultrasound signals. This interference with the ultrasound transmissions through the gas will cause
inaccurate flow rate measurements. In addition, temperature gradients in the gas flow may result in erratic or
inaccurate flow rate readings.
2. THE GAS MUST NOT EXCESSIVELY ATTENUATE ULTRASOUND SIGNALS. Some gases (i.e., high-purity carbon dioxide,
hydrogen, helium, etc.) readily absorb ultrasound energy. In these cases an “E1” will appear on the screen to
indicate that the ultrasonic signal is insufficient for reliable measurements.
3. THE GAS SOUND SPEED MUST NOT VARY EXCESSIVELY. The TransPort will tolerate relatively large, changes in gas
sound speed due to changes in gas composition and temperature. However, such changes must occur slowly.
Rapid fluctuations in the gas sound speed, to a value that is considerably different from that programmed into
the PT878GC, will result in erratic or inaccurate flow rate readings. Refer to Chapter 4, Programming Site Data .
10.1.3.2 Pipe Problems
Improper pipe conditions and/or flowcell installation can cause problems with measurement of the gas flow.
Contact Panametrics Sensing if you cannot solve pipe-related problems. By far, the most common pipe problems
are the following
1. THE COLLECTION OF MATERIAL AT THE TRANSDUCER LOCATION(S). Accumulated debris at the transducer
location(s) will interfere with transmission of the ultrasound signals. As a result, accurate flow rate
measurements are not possible. Realignment of the flowcell or transducers often cures such problems. Refer to
Chapter 3 for proper transducer installation.
2. INACCURATE PIPE MEASUREMENTS. The accuracy of the flow rate measurements is no better than the accuracy of
the programmed pipe dimensions. For a flowcell supplied by Panametrics Sensing, the correct data will be
included in the documentation. For other flowcells, measure the pipe wall thickness and diameter with the same
accuracy desired in the flow rate readings. Also, check the pipe for dents, eccentricity, weld deformity,
straightness and other factors that may cause inaccurate readings. Refer to Chapter 4, Programming Site Data ,
for instructions on programming the pipe data.