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 ( c ) C a l i b r a t i o n . C a l i b r a t i o n of the turbine rotor is performed by the
manufacturer. T h e rotor cannot be calibrated by the user. Meter electronics
r e q u i r e initial scaling and resealing each time a rotor is replaced. Scaling
information is provided by the manufacturer.
( d ) Maintenance. Required routine maintenance is the replacement of the
t u r b i n e rotor each 6 months to 1 year, or when a failure occurs. Failure will
b e catastrophic: occurring within 30 minutes or less. Maintenance is
performed only in the event of a failure.
( e ) O u t p u t . The turbine meter outputs an analog signal (4-20mA), which
can be recorded on a strip chart recorder or data logger, and a digital signal
(10V peak-to-peak) in the range of 0-1,500 Hz. Pressure and temperature
compensation are integral to the unit.
( f ) I n s t a l l a t i o n . The insertion turbine meter can be installed by a hot
tapping procedure, without securing the steam system. Maintenance can be
p e r f o r m e d without interruption of steam service. An upstream straight pipe
run of 10 diameters is required.
3.2.4 Vortex Shedding Meters. Vortex shedding meters operate by measuring
o s c i l l a t o r vortex shedding frequency for flow around an object in the flow
s t r e a m (figure 3-13). The foll o w i n g - i t e m s are characteristics of vortex
shedding meters.
( a ) A c c u r a c y . A c c u r a c y i s typical %1 percent full scale with a
turndown between 8:1 and 15:1, depending on flow rate and pipe size.
( b ) S i z i n g . Sizes are available up to 8 inches. The velocity of steam
i n the pipe must be relatively high, possibly requiring a pipe size reduction
before and after the meter.
(c) Calibration.
The vortex shedding meter is calibrated by the
manufacturer.
( d ) Maintenance. T h e r e are no moving parts. Therefore, after initial
setup maintenance is unnecessary unless component failure occurs.
( e ) O u t p u t . O u t p u t is digital from the meter to t r a n s m i t t e r . The
transmitter converts the digital meter signal to an analog signal that is
c o m p a t i b l e with either a strip chart recorder or a data logger.
( f ) I n s t a l l a t i o n . I n s t a l l a t i o n requires securing the steam system to
install the meter between two flanges in the steam line
If velocities are
not sufficient for the vortex meter, the size of the pipe upstream and
downstream of the meter must be reduced to increase velocity. The vortex
m e t e r is extremely sensitive to swirl or abnormalities in the flow profile,
and the meter may require up to 40 diameters downstream of an obstruction or
change in direction of the steam line. An upstream straight line pipe run of
10 to 20 diameters is required.
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