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4-20mA Signal scaling
Note:
The 4-20mA can be set to represent a particular flow range. It is also possible to enter a negative figure for
the minimum output and this would enable a reverse flow to be monitored.
4-20 mA OUTPUT
DD-MM-YY HH:MM:SS
4-20 mA O/P is ON
Dim: mm
mA Output Reading
:
0.00
Output Range
:
4-20
Units
:
l/min
Flow at max. output
:
0.00
Flow at min. output
:
0.00
Output mA for error
:
22.00
Exit
7. With the instrument operating in the FLOW
READING mode, press the 4-20mA function key.
This will access the 4-20mA OUTPUT screen.
8. Select Flow at max. output and enter a value of the
flow rate that you want to associate with a 20mA
output.
9. Select Flow at min. output and enter a value of the
flow rate that you want to associate with a 4mA
output.
This could be ‘0’.
10. Select Output mA for error and enter a value (max of about 23mA) that you want the 4-20mA output to produce
in the event of an error (e.g. if the flow-rate is outside the set range).
11. Upon completion press ENTER to return to the FLOW READING screen.
3.7.5 How to convert the measured current to flow rate
Assume the maximum flow rate is
F
max
(l/min) and the minimum flow rate
F
min
is ‘0’ (l/min), as shown.
To calculate the flow rate (l/min) for a measured current I(mA) then:
0-20mA
Flow rate
I
F
max
F
min
–
(
)
×
20
-------------------------------------------
F
min
+
=
0-16mA
Flow rate
I
F
max
F
min
–
(
)
×
16
-------------------------------------------
F
min
+
=
4-20mA
Flow rate
I
4
–
(
)
F
max
F
min
–
(
)
×
16
( )
---------------------------------------------------------
F
min
+
=
4
8
12
16
20
F
max
Flow (l/min)
I
(mA)
F
min
[0-16mA scale]
[0-20mA scale]
[4-20mA scale]
