N-Method Installation; Installationcheckup; Signalstrength; Signal Quality - Omega FDT-25 User Manual

14 FDT-25 Handheld Ultrasonic Flowmeter
§2.8.5 N-method Installation
Rarely used method.
§2.9 Installation Checkup
Through the checkup of the installation, one can: check the receiving signal strength, the signal
quality Q value, the traveling time difference of the signals, the estimated liquid speed, the measured
traveling time of the signals and the calculated traveling time ratio. Therefore, optimum measurement
result and longer running time of the instrument can be achieved.
§2.9.1 Signal Strength
Signal strength indicates the amplitude of receiving ultrasonic signals by a 3-digit number. [000]
means there is no signal detected, and [999] refers to the maximum signal strength that can be
received.
Although the instrument works well if the signal strength ranges from 500 to 999, stronger signal
strength should be pursued, because a stronger signal means a better result. The following methods
are recommended to obtain stronger signals:
(1) Relocate a more favorable location, if the current location is not good enough for a stable and
reliable flow reading, or if the signal strength is lower than 700.
(2) Try to polish the outer surface of the pipe, and apply more coupler to increase the signal strength.
(3) Adjust the transducers both vertically and horizontally while checking the varying signal
strength, stop at the highest position, and then check the transducers spacing to make sure the
transducers spacing is the same as what the M25 shows.
§2.9.2 Signal Quality
Signal quality is indicated as the Q value in the instrument. A higher Q value would mean a higher
Signal and Noise Ratio (short for SNR), and accordingly a higher degree of accuracy would be
achieved. Under normal pipe condition, the Q value is in the range 60-99, the higher the better.
Causes for a lower Q value could be:
(1) Interference of other instruments and devices such as a powerful transverter working nearby.
Try to relocate the flow meter to a new place where the interference can be reduced.
(2) Bad sonic coupling for the transducers with the pipe. Try to apply more coupler or clean the
surface, etc.
(3) Pipes are difficult to be measured. Relocation is recommended.
§2.9.3 Total Transit Time and Delta Time
The numbers displayed on menu window M93 are called total transit time and delta time respectively.
They are the primitive data for the instrument to calculate the flow rate inside the pipe. So the
flow rate indication will vary accordingly with the total time and delta time.