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F-1500 Turbine Flow Meter Manual 02/18 - 1018-6 / 35726
Page 26
Figure 20. Load Resistance Versus Input Voltage
R
L
> 250
4-20 mA voltage = +V
For Hart communications,
signal loop must have a
minimum of 250 ohms load
resistance R
L
.
mA
Meter
Figure 21. Isolated 4–20 mA Output Using External Power Supply
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, subtract the minimum terminal voltage
from the supply voltage and divide by the maximum loop current, 20 mA. Thus:
The maximum resistance R
load
= R
max
= (V
supply
– 12V) / 0.020 A
DC powered meters only
R
L
> 250 Ohm
DC Power
DC Common
mA Meter
For HART
communications
the signal loop
must have a
minimum of 250
ohms load
resistance.
Figure 22. Non-Isolated 4–20 mA Output Using Meter Input Power Supply
AC units only
Meter Provided DC
Power
R
L
> 250 Ohm
24 VDC
24 VDC
For HART
communications
the signal loop
must have a
minimum of 250
ohms load
resistance.
mA Meter
Figure 23. Isolated 4–20 mA Output Using Meter Provided Power Supply