401-405 SERIES - 11 -
Since the alarms act as switches they do not produce
a voltage or current signal. However, they can be
used to generate a voltage signal on an Alarm Out
line. This is done by connecting a suitable pull-up
resistor between an external voltage supply and the
desired alarm line while connecting Alarm Common
to the common of the power supply. When activated,
the alarm line voltage will be pulled toward the alarm
common line generating a sudden drop in the signal
line voltage.
To use the alarm to illuminate an LED connect the
positive terminal of the LED to a suitable power
supply and connect the other end to a current
limiting resistor. This resistor should be sized such
that the current is less than 20 mA when the entire
supply voltage is applied. Connect the other end of
the resistor to Alarm 1 or Alarm 2. Connect Alarm
Common to the circuit common of the power supply. When activated, the alarm line is pulled toward
the alarm common generating sufficient current through the LED to cause it to illuminate.
Figure 2-10 shows an example of the LED circuit arrangement applied to Alarm 1 while Alarm 2 is
configured with a suitable pull-up resistor to provide a voltage output on an Alarm Out line.
Since the Alarm Common is a
shared contact, if both alarms
are being used independently
they must each be wired such
that the current passes
through the external signaling
device before reaching the
alarm line.
The alarm settings and
activation status are available
via software commands and
queries. The software
interprets an activated Alarm
1 as an “Alarm” condition,
while an activated Alarm2 is
interpreted as a “Warning”
condition. The software
manual includes the detailed
descriptions for configuring
and interpreting the activation
of these alarms.
2.9. Auxiliary Input
Connection
The Hastings 400 Series flow meters provide an auxiliary analog input function. The flow meter can
read the analog value present between pins 5 and 6 on the terminal strip (as shown in Figure 2-2) and
make its value available via the digital interface. The accepted electrical input signal is the same as that
configured for the analog output signal (4 – 20 mA, 0 -20 mA, 0-5 Vdc, 1-5 Vdc, or 0-10 Vdc). Unlike
the analog output signal, which is isolated and capable operating at common mode offsets of over
1000V, the analog input signal cannot be galvanically isolated from ground potential.
Alarm
1
Alarm 2
Alarm
Common
V +
Alarm Out
V -
Figure 2-10 Alarm circuit diagram for LED operation
Alarm 1
Alarm 2
Alarm Common
Figure 2-9 Alarm circuit diagram
