Sierra INNOVA-MASS 241-VTP - Manual (Page 37)

Series 24-HP Instruction Manual Chapter 2 Installation
IM-24-HP 2-23
Alarm Output Connections
One alarm output (Alarm 1) is included on the standard Innova-Mass™
Flow Meter. Two or more alarms (Alarm 2 and Alarm 3) are included on
the optional communication board. The alarm output optical relays are
normally-open single-pole relays. The relays have a nominal 200 volt/160
ohm rating. This means that each relay has a nominal on-resistance of 160
ohms and the largest voltage that it can withstand across the output ter-
minals is 200 volts. However, there are current and power specifications
that must be observed. The relay can conduct a current up to 40 mA and
can dissipate up to 320 mW. The relay output is isolated from the meter
electronics and power supply. When the alarm relay is closed, the current
draw will be constant. Make sure to size R
load
appropriately.
There are three connection options for the alarm output–the first with a sep-
arate power supply (Figure 2-23), the second using the flow meter power
supply (Figure 2-24)(DC powered units only) and the third with the meter
provided power supply (Figure 2-25)(AC powered units only). Use the first
option with a separate power supply (5 to 36 VDC) if a specific voltage is
needed for the alarm output. Use the second configuration if the voltage at
the flow meter power supply is an acceptable driver voltage for the load
connected. (Take into account that the current used by the alarm load comes
from the meter’s power supply). Use the third if you have an AC powered
unit only. In any case, the voltage of the alarm output is the same as the vol-
tage supplied to the circuit.
The alarm output is used for transmitting high or low process conditions
as defined in the alarm settings (see page 3-7).
Figure 2-23. Isolated Alarm Output with External Power Supply
Figure 2-24. Non-Isolated Alarm Output Using Internal Power Supply