User manual

41
MC-III™ EXP Flow Analyzer Section 3
Conguring the 4-20 mA Rate Output
Caution: Before performing any 4-20 mA conguration, ensure that all peripheral equipment con-
nected to the 4-20 mA current loop is either disconnected or disabled. Conguring and
testing the 4-20 mA output feature on the MC-III EXP with the peripheral equipment in
operation may cause false alarms or erroneous operation of the peripheral device or as-
sociated equipment.
The MC-III EXP has a 4-20 mA output feature that represents ow rate. Zero and full-scale values can be
congured to represent any ow rate range within the range of the owmeter.
The low (or zero) setting is the ow rate value that will produce a 4-mA output. The high (or full-scale)
setting is the ow rate value that will produce a 20-mA output. Typically, the high value is greater than the
low value, as shown in Figure 3.2.
Figure 3.2—4-20 mA output conguration
See Analog (4-20 mA) Rate Output, page 31, for instructions on installing and wiring the 4-20 mA rate output.
Flow rates between the minimum and maximum rate setpoints will result in an output of current between
4 mA and 20 mA according to the following calculation:
[ ]
[ ]
MAX MIN
OUT CURR MIN
I I
I RATE Low I
High Low
−
= × − +
−
Where:
I
OUT
= output current
I
MAX
= maximum current output (20 mA)
I
MIN
= minimum current output (4 mA)
High = programmed ow rate that produces a 20-mA output
Low = programmed ow rate that produces a 4-mA output
RATE
CURR
= ow rate