Dynasonics TFX Ultra Transit Time Flow Meters Manuel d'utilisateur télécharger pdf (Page 28)

INPUTS/OUTPUTS

General

The flow metering system is available in two general configurations. There is the standard flow meter model that is equipped

with a 4-20 mA output, two open collector outputs, a rate frequency output, and RS485 communications using the Modbus

RTU command set.

The energy version of the flow metering family has inputs for two 1000 Ohm RTD sensors in place of the rate frequency and

alarm outputs. This version allows the measurement of pipe input and output temperatures so energy usage calculations can

be performed.

4-20 mA Output

The 4-20 mA output interfaces with most recording and logging systems by transmitting an analog current signal that is

proportional to system flow rate. The 4-20 mA output is internally powered (current sourcing) and can span negative to

positive flow/energy rates.

For AC powered units, the 4-20 mA output is driven from a 15V DC source located within the meter. The source is isolated

from earth ground connections within the flow meter. The AC powered model can accommodate loop loads up to 400 Ohms.

DC powered meters utilize the DC power supply voltage to drive the current loop. The current loop is not isolated from DC

ground or power. Figure 23 shows graphically the allowable loads for various input voltages. The combination of input voltage

and loop load must stay within the shaded area of Figure 23.

200

100

300

400

500

600

700

800

900

1000

1100

10 12 14 16 18 20 22 24 26 28

Supply Voltage (VDC)

Loop Load (Ohms)

Operate in the

Shaded Regions

Supply Voltage - 7 VDC

0.02

= Maximum Loop Resistance

Figure 23: Allowable loop resistance (DC powered units)

INPUTS/OUTPUTS

Page 28 March 2014

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Dynasonics TFX Ultra Transit Time Flow Meters Manuel d'utilisateur Page 28