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In many applications using insertion flowmeters, severe turbulence creates a problem in reading FT420 flow computers.  The constantly (and rapidly) changing flow rate is faithfully measured by the insertion flowmeter and communicated to the flow computer.  The FT420 flow computers in turn translate 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 flow 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 flow 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 flow 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 flow 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 flow computer
To increase the flowmeter's filtering, follow these steps:
  1. 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.
  2. Press and hold all three keys down for 5 seconds minimum. This will cause the display to change to "J0".
  3. Press the SET key one more time. This will change the display to "F4" (default factory setting).
  4. Press the up arrow key to increase the flow 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.
  5. Press the SET key one more time to return to the time units setting display.  Continue to press until the flow computer returns to the rate/total display of normal operation.

Please visit our flowmeter pages for more information on our flowmeters.
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