How To Use The Set Empty Command; Zero Flow Adjust Menu; Autozero; Actual Zero - Siemens SITRANS F Operating Instructions Manual

Section 2

How to Use the Set Empty Command

Use the Set Empty command to enter a number that represents the signal strength level consistent
with an empty pipe. Set Empty uses non-linear scaling. There is no direct correlation between the
number you enter and any standard amplitude unit. If you set the number too low, the meter may not
detect a true empty pipe. If you set it too high, it could trigger the empty pipe alarm, suspending flow
measurement, even though the liquid is flowing.
To enter an Empty Pipe Alarm Threshold:
To access the [Empty Pipe Set] option list press
To move the cursor to [Set Empty] press
ENT
Press . The current empty threshold number appears in a pop-up window.
Use the numeric keys to type a new Set Empty number.
To store the Set Empty number press
2.4.11

ZERO FLOW ADJUST MENU

Unlike turbine meters ultrasonic transit-time meters 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 transducers. Consequently some flow offset (or zero offset)
may be present in any installation. To eliminate this residual zero offset Controlotron 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 1011 transducers are mounted in the Reflect Mode configuration (see paragraph 3.1.5) 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 compo-
nent 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 Up and Down transducers 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 transducers cannot be mounted in the
Reflect Mode configuration. Flow must be stable during the entire process.
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