Onicon F-2600 Manual de usuario descargar pdf (Pagina 43)

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F-2600 & F-2700 Vortex Flow Meter Manual 02/15 - 0808-7 / 19204 Page 43

2.7.2 4-20 mA OUTPUT CONNECTIONS

The externally powered versions of the meters have a single 4-20 mA loop powered

output. Two additional loops are available on the optional communication board. 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 require a

minimum of 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 30. The 4-20 mA loop is optically isolated from the

ow meter electronics.

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

Figure 30. Load Resistance Versus Input Voltage

250

4-20 mA voltage = +V

For Hart communications,

signal loop must have a

minimum of 250 ohms load

resistance R

Meter

Figure 31. Isolated 4–20 mA Output Using External Power Supply

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Onicon F-2600 Manual de usuario Pagina 43