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FLOWMETERS: SETTING THE FT420 FOR HIGH-TURBULENCE FLOWMETER APPLICATIONS
In many applications using insertion flowmeters, severe
turbulence creates a problem in reading an FT420 flowmeter computer. The constantly (and rapidly) changing flow
rate is faithfully measured by the insertion flowmeter and communicated to the flowmeter’s computer. The FT420
flowmeter computer 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 measured by the flowmeter over
some time period. The flowmeter rate reading on the other hand may be almost unusable due to rapid fluctuations
up and down. Every FT420 flowmeter computer 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 to all FT420 flowmeter computers, which allows a
field change to the degree of filtering, to allow adaptation for severe cases.
It should be noted that there is a trade-off to increasing the degree of filtering used on the flowmeters. While it
smoothes fluctuations in the flowmeter computer display, it also slows down flowmeter’s response time, which also
effects the response time of the 4-20 mA analog output. For this reason, the degree of filtering applied to the
flowmeter computer should only be increased as much as is necessary to provide a readable display. Under
normal circumstances, the flowmeter’s factory setting should be suitable without change.
Setting the FT420 flowmeter computer
To increase the flowmeter’s filtering, follow these steps:
- Press the SET key on the flowmeter until the time units setting is reached. This is the setting for
changing time units, as shown by the currently-selected unit (SEC, MIN, HR, DAY) blinking.
- Press and hold all three keys down for 5 seconds minimum. This will cause the display to change to "J0".
- Press the SET key one more time. This will change the display to "F4" (default factory setting).
- Press the up arrow key to increase the flowmeter computer’s filter value and the left arrow key to decrease
the filter value. The maximum is 9; the standard factory flowmeter setting is 4. Release the up
arrow when the desired value is reached.
- Press the SET key one more time to return to the time units setting display. Continue to press until
the flowmeter computer returns to the rate/total display of normal operation.
Please visit our flowmeter pages for more information on these products.
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