|
| Tech Bulletin: Setting the FT420 for High-Turbulence
Applications
In many insertion flow metering applications, severe turbulence creates
a problem in reading an FT420 flow computer. The constantly (and rapidly)
changing flow rate is faithfully measured by the insertion sensor impeller
and communicated to the flow computer. The FT420 in turn translates
this into a flow rate and total. It is often the case that the total
in this type of installation will be reasonably accurate, since it is
an average of the flow velocities over some time period. The rate reading
on the other hand may be almost unusable due to rapid fluctuations up
and down. Every FT420 comes standard with an internal filtering function
which is designed to slow down these fluctuations and give something
more closely resembling an average flow rate. In response to requests
from customers, a hidden function was added which allows a field change
to the degree of filtering, to allow adaptation for severe cases. This
function is available on units purchased during or after August of 2001.
(To determine date of manufacture from the serial number, look at the
first 4 digits. They correspond to MM/YY.)
It should be noted that there is a trade-off to increasing the degree
of filtering. While it smooths fluctuations in the display, it also
slows down response time, which also effects the response time of the
4-20 mA analog output. For this reason, the degree of filtering should
only be increased as much as is necessary to provide a readable display.
Under normal circumstances, the factory setting should be suitable without
change. Setting the FT420 To increase filtering, follow these steps:
|