Siemens FUS1010, Operating Instructions Manual, Page: 110 / 298

Functions
7.3 Zero Flow Adjust Menu
FUS1010 IP65 NEMA 4X & IP66 NEMA 7
Operating Instructions, 01/2013, A5E02951520-AC
109
7.3 Zero Flow Adjust Menu
Zero Flow Compensation Methods
Unlike turbine flow meters ultrasonic transit-time flow meter provide active flow measurement
right down to zero flow, however, the measurement of the transit-time delta is dependent on
the similarity or "match" of the electronics, cables and ultrasonic sensors. Consequently
some flow offset (or zero offset) may be present in any installation. To eliminate this residual
zero offset Siemens has developed several different methods to insure proper zero flow
compensation. The following paragraphs describe each method and when they should be
used.
AutoZero
When the 1011HP sensors are mounted in the Reflect Mode configuration the AutoZero
routine is automatically invoked at the end of the Initial Makeup. Flow does not have to be
stopped to perform AutoZero since only the pipe wall signal is used in determining the zero
offset and not the liquid component. The AutoZero routine performs a one-time analysis of
the pipe wall component of the ultrasound signal to quantify any residual mismatch in the
hardware. Once the AutoZero routine is complete, the system memorizes this measured
zero offset and subtracts this value from the flow reading.
Actual Zero
The Actual Zero function simply averages the indicated "zero flow" readings (over a user
defined time period) then stores this average value in memory. Under normal operation the
indicated flow reading is zero compensated by simply subtracting this memorized value from
the uncompensated flow reading. Actual Zero is the most positive method for zeroing the
system; however, flow must be stopped with the line blocked (if possible) before invoking this
function. If stopping flow is not possible then an alternate zeroing method should be
selected.
ReversaMatic
This routine involves swapping the Upstream and Downstream sensors on the pipe (while
keeping the cables attached) such that the difference in the transit-time change represents
the zero offset. The fixed zero offset value is stored in memory in the same manner as
described in Actual Zero. This routine would generally be used whenever flow cannot be
stopped and the sensors cannot be mounted in the Reflect Mode configuration. Flow must
be stable during the entire process.