KROHNE OPTIMASS with MFC 05x EN - Manual (Page 79)

Installation and Operating Instructions OPTIMASS 78
5.3 Menu 3- Configuration Menu
To access this menu, enter programming mode
Display Key
Line 1 Line 2
→ Fct. 1 Operation
↑ Fct. 2 Test
↑ Fct. 3 Config.
→ Fct. 3.1 Basic Param.
→ Fct. 3.1.1 Low Flow cut off
Low Flow Cut Off Fct. 3.1.1
If the flow mode in (Fct. 3.1.3. is set to Flow +/- then at zero flow small signal fluctuations will average out
to nothing and the totaliser will remain static.
However, if ‘unidirectional’ flow is selected, this process will not work and the totaliser reading will
increment slowly with time. To prevent this, the Low Flow cut off should be set.
The Low Flow cut off is entered as a percentage of the rated nominal flow of the primary head. The cut off
may be set from 0 to 10% in increments of 0.1%. Thus for example a 7000 T25 (nominal flow 34500 kg/h
or 1250 lbs/min) with a low flow cut off of 0.2%, any flow less than 69kg/hr or 2.5 lb/min will indicate zero
on the display.
To set the low flow cut off to 1%:
Display Key
Line 1 Line 2
From Fct. 3.1.1 Low Flow cut off
→ (0)0.5 Percent
→ (0).5 Percent
→ (1).5 Percent
→ 1.(5) Percent
↑ Repeat till (0) then
↵ to accept the value.
Time Constant Fct. 3.1.2
Measurements taken from the sensor are digitally filtered to provide stable readings in the event of
fluctuating flows. The degree of filtering also affects the response time of the reading due to rapid
changes in the flow.
Short time constant:
•
Fast response
• Fluctuating reading
Long time constant:
•
Slow response
• Stable reading
The figure below shows the typical response of the measurement for varying time constants and a rapid
change in flow.