1. Fluid Details
   • What is the fluid flowing through the pipes. Do you have the appropriate sound speed and kinematic viscosity figures for the fluid (See reference below)
   • Does the liquid fill the pipe? If the pipe is NOT full the PT878 will not work.
   • Is the liquid clean. The 'time of flight' measurement technique relies on the fluid being relatively clean. It can cope with a percentage of impurities however the more particles in the liquid the less likely the technique will work!
2. Pipe
   • Do you know the dimensions of the pipe. The diameter and wall thickness (See reference below)
   • What is the pipe made of and what is the sound speed in that material (See reference below)
3. Physical Layout (the flow must be laminar...)
   • Are there 10 pipe diameters upstream from where the flowmeter is to be mounted
   • Are there 5 pipe diameters downstream from where the flowmeter is to be mounted

If you cannot successfully answer the above questions then you cannot guarantee the operation of the PT878 flowmeters. However these flowmeters will often work anyway. This technique has an advantage such that if it does work then you can believe the reading..

These are some additional comments from the PT878 manual

1. Fluid Problems
   • THE FLUID MUST BE HOMOGENOUS, SINGLE PHASE, RELATIVELY CLEAN, and FLOWING STEADILY. Solid particles and gas bubbles absorb and disperse ultrasound. Although, in some cases, solids and gases have little effect on the operation of the TransPort, excessive amounts will prevent ultrasound transmission through the fluid and interfere with proper flow measurement. Temperature gradients may also cause a problem.
   • THE FLUID MUST NOT CAVITATE NEAR THE FLOWCELL. Fluids with a high vapour pressure may cavitate near or in the flowcell. This causes problems resulting from gas bubbles in the fluid. Cavitation can usually be controlled through proper installation design.
   • THE FLUID MUST NOT ATTENUATE ULTRASOUND EXCESSIVELY. Some fluids, particularly those that are very viscous, absorb ultrasound energy. In these cases an “E1” will display on the screen to indicate that the ultrasonic signal is not of sufficient strength for reliable measurements.
   • THE FLUID SOUND SPEED MUST NOT VARY EXCESSIVELY. The TransPort will tolerate relatively wide, but slow, changes in fluid sound speed due to changes in fluid composition and temperature. However, if you are measuring a fluid that is considerably different from the fluid programmed into the TransPort, you may have to adjust the meter for the new fluid.
2. Pipe Problems
   • THE INSIDE OF THE PIPE OR FLOWCELL MUST BE RELATIVELY CLEAN. Excessive build up of scale, rust, or debris will interfere with flow measurement. Generally, a thin coating or a solid well-adhered buildup on the pipe wall will not cause problems. Loose scale and thick coatings (such as tar or oil) will interfere with ultrasound transmission and may result in incorrect or unreliable measurements.
   • THE FLOWCELL ORIENTATION MUST NOT ALLOW SEDIMENT OR GAS ENTRAPMENT AT THE TRANSDUCER LOCATIONS. Sediment or gas trapped in the transducer ports for wetted transducers, or at the transducer locations for clamp-on transducers, will interfere with flow measurement. Realignment of the flowcell or transducers often cures these problems. In some cases different transducers may be used that protrude into the flow stream.
   • THE PIPE OR FLOWCELL DIMENSIONS MUST BE ACCURATE. The accuracy of your flow measurements will be no better than the accuracy of your programmed pipe or flowcell dimensions. If GE Infrastructure Sensing did not supply your flow cell, the dimensions you program must be consistent with the required flow accuracy. Check your pipe for wall thickness, diameter, dents, eccentricity, weld deformity, and straightness.
   • THE PIPE SURFACES SHOULD BE SMOOTH (FOR CLAMP-ON). When using clamp-on transducers, both the inside and the outside of the pipe at the transducer locations must be smooth. If the pipe is extremely rough, the ultrasonic signal will be scattered by the rough surface, and will not be received by the flowmeter, preventing flow measurement.
   • THE PIPE MUST ALLOW ULTRASOUND TO PASS THROUGH (FOR CLAMP-ON). Some pipe materials or linings such as Fibreglass (or generic fibre reinforced pipe), Teflon, and polyethylene, absorb ultrasound and may cause problems in clamp-on applications. Pipes with extremely thick walls or high OD to ID ratios may also present difficulties.
3. Installation Problems
   • POOR COUPLING TO PIPE Clamp-on transducers must be in intimate contact with the pipe. The pipe wall must be smooth and generally free of paint. The couplant material must fill voids between the transducer and the pipe, and must be firmly coupled or bonded to both the pipe and the transducer. The pipe and transducer must be clean and dry for permanent couplant, such as grease or epoxy, to adhere properly. Enough pressure must be applied to the transducer by its clamp to hold it firmly against the pipe.
   • MISALIGNMENT. The transducer transmits relatively narrow beams of ultrasound, and therefore transducer alignment is critical to assure that the beam can travel from one transducer to the other without undue attenuation. Be sure to exactly follow the instructions that came with your transducers and clamping fixtures. Also, be sure that the transducer spacing agrees with the calculated spacing (S).
   • INTERNAL DAMAGE Ultrasonic transducers consist of a ceramic “crystal” bonded to the transducer case. The bond between the crystal and the case may be damaged by extreme shock and by temperature extremes. The crystal itself can also be damaged by the same conditions. The internal wiring can be corroded or shorted if contaminants enter the transducer housing.
   • PHYSICAL DAMAGE Transducers may be physically damaged by dropping them onto a hard surface or striking them against another object. Usually the connector on the transducer is the part that is damaged, as it is the most fragile. Minor damage may be repaired by carefully bending the connector back into shape. If the connector cannot be repaired, replace the transducers. Note that transducers must be replaced in pairs, and that after replacement the flowmeter parameters should be checked.
   • CYCLE SKIP CONDITION A cycle skip is usually caused by a distorted or altered signal due to poor couplant, bad wall, or unusual fluid disturbances. To resolve a cycle skip, recouple both transducers with proper couplant. Try standard CPL-1 couplant that is good to 100°C (212°F) or CPL-2 for up to 260°C (500°F). In addition, make sure the pipe wall is free of paint and rust.