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5.8.3 Flow Alarm
The Alarm output is enabled by selecting ‘ALARM’ from the digital output menu. The alarm
output may be configured as a ‘High Alarm’ which will trigger in the event the flow rate
exceeds the alarm set-point, a ‘Low Alarm’ which will trigger in the event the flow rate drops
below the set-point, or a ‘High/Low Alarm’ which is a combination of the two.
Configuration of the Alarm involves selecting the type of alarm, entering the alarm set-point
(specified in Rate units, e.g. L/min), and entering the hysteresis value.
The Alarm hysteresis is an adjustable buffer zone around the set point which allows the user to
overcome alarm chattering when the flowrate is fluctuating around the set-point. If you find
that your flow alarm is repeatedly switching on/off it is possible you need to set a higher value
for hysteresis.
The hysteresis setting is entered as a percentage of the set-point value. For example, a
100L/min High Flow Alarm with 5% hysteresis will trigger ON at 100L/min but will not turn OFF
until the flow drops to below 95L/min.
Notification that a Flow Alarm has been triggered is typically done through an external light or
siren wired to the output terminals of the display. Alternatively, the output from the display
can be connected to an external control system such as a PLC. In addition, the backlight may
be used in ALARM mode, which allows the display backlight to flash in the event of an alarm.
5.9 Advanced Options Menu
5.9.1 Resetting Accumulated Total
Resetting the accumulated total can only be done at this level of the Advanced Menu. If the
display is PIN protected it will not be possible to reset the accumulated total. Once the
accumulated total is reset it is not possible to recover the value which was in the accumulated
total – it is advisable to record the accumulated total value before resetting.
5.9.2 Low Frequency Cut-Off
The low frequency cut-off parameter is used to adjust the minimum frequency required for
the rate display. This setting is useful to avoid spikes in the rate display from “apparent flow”
which could be caused by movement of liquid in the pipes of a mobile installation (on a truck
etc.), pulsations from a dead-headed pump, etc.
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