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F-1500 Turbine Flow Meter Manual 02/18 - 1018-6 / 35726
Page 22
2.5.2 4-20
mA OUTPUT CONNECTIONS
The loop powered 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 requires at least 12 volts at the
input terminals to operate correctly.
The maximum loop resistance (load) for the current loop output is dependent upon the
supply voltage and is given in Figure 18. 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 Rl
oad
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
Figure 10. Load Resistance Versus Input Voltage
2.5.3 Frequency Output Connections
The frequency output is used for a remote counter. It can be scaled to output a 1 to 10 kHz
signal proportional to mass or volume flow, temperature, pressure or density.
The frequency output requires a separate 5 to 36 VDC power supply and there are current
and power specifications that must be observed when using this output. The output can
conduct a current up to 40 mA and can dissipate up to 200 mW. The output is isolated
from the meter electronics and power supply.
Freq. Out -
Freq. Out +
Freq. Out voltage = +V
Select resistor so that current
through Freq. Out <= 40 mA
Figure 11. Isolated Frequency Output Using External Power Supply
Freq. Out voltage = +V
Select resistor so that current through Freq. Out <= 40 mA
Freq. Out +
Freq. Out -
Figure 12. Non-Isolated Frequency Output Using External Power Supply