Sierra INNOVA-FLO 220 - Manual (Page 34)

Chapter 2 Installation Series 220/221 Instruction Manual
4-20 mA Output Connections
The Innova-Flo meter has a single 4-20 mA loop. The 4-20 mA loop current
is controlled by the meter electronics. The electronics must be wired in series
with the sense resistor or current meter. The current control electronics re-
quire 12 volts at the input terminals to operate correctly.
The maximum loop resistance (load) for the current loop output is depend-
ent upon the supply voltage and is given in Figure 2-16. The 4-20 mA loop
is optically isolated from the flow meter electronics.
R
load
is the total resistance in the loop, including the wiring resistance (R
load
=
R
wire
+ R
sense
). To calculate R
max
, the maximum R
load
for the loop, use the
maximum loop current, 20 mA. The voltage drop in the loop due to resis-
tance is 20 mA times R
load
and this drop is subtracted from the input voltage.
Thus:
The maximum resistance R
load
= R
max
= 50 * (V
supply
– 12V).
Figure 2-15. Load Resistance Versus Input Voltage
2-20 IM-22