Gas- and Steam Flowcomputer
DigiFlow 515
Operating Manual
35
11 Options
11.1 Analog output
The 0/4-20mA output option provides an scaled analog output to one of the listed parameters below:
Computer function:
Selectable parameter:
Gas flow correction
Volume flow, mass flow, temperature, pressure, (Kompressibilitly factor z
f
of
natural gas)
Steam flow correction
Mass flow, energy flow, temperature, pressure
Steam flow correction with
energy balance
Mass flow total, up- or downstream, energy flow total, up- or downstream,
temperature up- or downstream, pressure up- or downstream, specific vol-
ume in up- or downstream, specific enthalpy in up- or downstream
All output signal are isolated from power source an signal inputs, to ensure minimum interference an high
reliability.
A block diagram of the output circuit is represented followingly, the various methods of connection have to be
found on the following sides.
Digital-
Analog-
Terminals
galvanic
Isolation
converter
DC/DC-Converter
+
+
-
-
23
24
+
-
Load
max. 500 Ohm
I
out
0/4...20mA
Fig. 16: Analog output circuit
Maximum load in output loop will be 500
Ω
.
The parameters for the analogous output are programmed at the configuration of the computer and serve:
Definition of corresponding min. value to 4 or 0mA output
Definition of corresponding max. value to 20mA output
Selection of output span
0–20mA –– 4–20mA
Since the output range can be chosen freely, the computer can be used also for the amplification of the input
signal e.g.. At the use of a writer can so instead of the illustration of the complete measuring range of e.g. 0-
200kg/min be represented a part extended of 100kg/min (corresponds 4mA) to 120kg/min (corresponds
20mA)
For flow rates or displayed values outside the maximum or minimum values, an output signal of 20 or 0/4mA
is issued.
The output signal is after approx. 0.8sec in agreement with the display udated. Between these update the
output remains constantly.
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