Fluid Components International MT91 Manual Operation User Manual
Page 15
CHAPTER 3 - OPERATION
FLUID COMPONENTS INTL
Doc. No. 003185 Rev. B
3 - 15
Model MT91 Multipoint Flowmeter
Figure 3-10 illustrates the effect of adding an offset of plus 1 ohm and adding an offset of minus 1 ohm to the raw
signal.
Delta-R versus Flow
Delta R (Ohms)
Flow (SF/S
)
0.00
20.00
40.00
60.00
80.00
100.00
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
Flow
Plus 1 Ohm
Minus 1 Ohm
Figure 3-10. Delta-R Versus Flow Rate
Ø To enter an offset value:
1.
Go to menu level 4.4.4 (Calibration
Þ
Cal Flow
Þ
Offset).
2.
Select 1=Offset Values. Enter sensing point number and value of desired offset. Units are always in ohms.
3.
Select 2=Enable Offset.
Applying the Filter
For applications with noisy flow profiles, the filter can be used to reduce jumps or oscillations in the output signal.
The flowmeter takes samples of the flow rate periodically at each active sensing point. If the current value jumps up
when the next sample is taken, applying the filter can help smooth this jump out. The rate at which a sample is taken
depends on the number of active sensing points. The more sensing points that are active, the longer the intervals
between samples.
The filter strength acts stronger with increasing interval time. A filter strength of 2 for a 4-point system takes twice
as long to apply than a filter strength of 2 for a 2-point system. See Figure 3-11.
Time
Flow Signa
l
0
5
10
15
20
25
30
35
40
45
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
2-point system, Filter = 2
4-point system, Filter = 2
No Filter
Vc
Vs
Vn
Figure 3-11. Effects of Filter on Flow Signal Versus Time