2-30
1010PVNFM-3A
Section 2
How to Use the Set Empty Command
Use [Set Empty] 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
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
2.4.10 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 com-
pensation. 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 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
TM
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 trans-
ducers
cannot be mounted in the Reflect Mode configuration. Flow must be stable during the
entire process.
ENT
ENT
To Next Page
Loading...
