MFC-CB™ Operation and Maintenance Manual
©2001~2007
DH Instruments, a Fluke Company
Page 88
Note that:
1. All values are device channel specific.
2. In some cases, the displayed set and measure values are in a unit of flow or %FS. In this
case they must be converted to and from electrical values prior to or just after the
electrical value calculations (see Section 7.1.2).
3. When the display unit of measure is
electrical
or %FS, K = 1 (has no effect).
7.1.2
CONVERTING BETWEEN ELECTRICAL UNITS AND FLOW
OR %FS UNITS
MFC-CB sets and reads electrical values to and from an MFC or MFM. When a custom MFC
profile is in use (see Section 3.3.1), a flow unit and range are specified in addition to the
electrical unit and range. In this case, MFC-CB can accept set point entries and display
measurement readings in a flow unit of measure.
•
To convert a set point entry made in a flow unit of measure to an electrical value
MFC-CB first converts the flow value into an electrical value and then follows the
electrical value to output in response to a user set point entry calculation to determine the
true electrical signal to output (see Section 7.1.1). The conversion of a flow unit entry
into an electrical value is made following:
0
,
0
,
,
,
S
S
S
S
S
S
F
FS
E
FS
F
act
E
act
+
−
⋅
=
Where:
S
act,E
= Set point electrical value
S
act,F
= Set point flow value
S
FS,E
= Electrical value output corresponding to full scale flow
S
0
= Electrical value output corresponding to zero flow
S
FS,F
= Full scale flow value
For example, if the MFC profile specifies a 0 to 5 V electrical range and a 0 to 100 sccm
flow range, a set point of 20 sccm is converted to an electrical value following:
]
[
1
]
[
0
]
[
100
]
[
0
]
[
5
]
[
20
,
V
V
sccm
V
V
sccm
S
E
act
=
+
−
⋅
=
or, if an MFC profile specifies a 4 to 20 mA electrical range and a 0 to 100 sccm flow
range, a set point of 20 sccm is converted to an electrical value following:
]
[
2
.
7
]
[
4
]
[
100
]
[
4
]
[
20
]
[
20
,
mA
mA
sccm
mA
mA
sccm
S
E
act
=
+
−
⋅
=
