Siemens SITRANS 7ME3500, Operating Instructions Manual, Page: 27 / 296

Description
3.4 Theory of Operation
FUE1010 IP65 NEMA 4X
Operating Instructions, 12/2014, A5E03086491-AC
25
Typical Applications
The typical applications of the flow meter for heat energy flow include:
● Chilled water
● Hot water
● Condenser water
● Lake source cooling
● Thermal storage
● Chemical feed flow
Typical Industries Serviced
● HVAC (Hotels, Airports, Government, District heating)
● Power Generation (Nuclear, Fossil, and Hydro)
● Chemical Processing
● Food and Pharmaceutical
● Aircraft Avionics and Ground Support
● Water and Wastewater
● Aerospace
● Automobile Manufacturing
● Hydrocarbon Industries
3.4 Theory of Operation
The liquid flow meter relies on the MultiPulse transit-time. Two WideBeam ultrasonic sensors
per measuring path, alternating as transmitter and receiver, are used to interrogate the liquid
flowing within the metering section. The resulting time of arrival for each direction of transmit
(upstream and downstream) is then measured using a highly accurate and stable digital
signal processing method.
Using this detection scheme, the flow meter is capable of resolving the relative transit-time
difference (dT) to within ±100 psec. Considering typical liquid flow transit-time differences
ranging from 1x10
4
to 1x10
6
psec, the flow meter is capable of providing an exceptional turn-
down ratio. The flow meter also incorporates a correlation technique which enables the
system to detect very high flow velocities with the same high degree of resolution. The
ultrasonic sensors are designed with sufficient beam divergence characteristics to insure that
the receive sensors will always have sufficient signal to maintain operation under conditions
of high beam blowing, a condition that occurs under very high flow velocities where the path
of the ultrasonic beam is actually blown past the receivable area of the sensors.
With accurate signal arrival time available, the flow meter can compute the raw flow velocity
from the measured upstream and downstream transit times.