Dwyer PUX - Manual (Page 105)

15 - 14
V. Others
1. What is the difference between a Doppler type flowmeter and the PUX meter ?
A Doppler type flowmeter emits ultrasonic waves and receives the waves reflected from foreign objects
in the fluid.
Velocity is measured utilizing the principle that the frequency deviation of the received waves from the
emitted ones is in proportion to the flow velocity (Doppler effect).
Therefore:
(1) The fluid must contain foreign objects (including air bubbles). It is not suited for clean water but
is suited for sewage.
(2) Since the position in the fluid where the reflection occurs is obscure, the amount and nature of
foreign objects in the fluid affect the measuring accuracy together with the velocity profile in the
piping.
The PUX unit is designed to measure the velocity with ultrasonic waves passing through piping. As
it measures an average velocity in the piping, it measures flow rate highly accurately.
The Doppler system has the above-mentioned disadvantage, but it is used to measure an approximate
flow from the outside of the piping, permitts liquids with large amount of foreign objects, and is effec-
tively used for liquids with slurry or air bubbles.
2. Life span of LCD
The life span of LCD is considered to be about l0 years under general operating conditions, accord-
ing to the manufacturer’s catalogue. Generally, it is about 5 to 6 years in actual service.
The life span is not so much related to the number of displaying operations.
3. Printer roll sheet
(1) Supplied printer roll sheet is 20 meters long.
The roll sheet is fed at 0.35 mm/dot.
Setting the paper feed at a cycle of 1 second uses a roll of paper in 57,140 sec. (about 15.87 hours)
= 20 m /0.35 mm.
(2) In case of TEXT mode
A single printing consists of the following:
q Date (1 line),
w Flow velocity, flow rate, and total (several lines),
e Measuring conditions (1 line)
r Paper-feed (1 line)
A printer has a paper fed at 2.8 mm/line.
For example, if you select flow rate (m3/h), flow velocity and +total, the paper feed totals 6 lines
(16.8 mm). If a printing cycle is assumed to set to 1 minute, a roll of paper will be used for 1190
minutes (about 19.8 hours) = 20 meters/16.8 mm