27
output the signal at the maximum of 100Hz, and all excess pulses will be stored in memory
until such a time that flow has stopped and the instrument can output the stored pulses – it is
not recommended that systems be designed to operate in this way under normal conditions.
The output frequency can be calculated as follows:
=
( )
(
)
60( )
If the system design does not allow significant periods of zero-flow where the instrument can
reduce the stored pulse count to zero it is advisable to increase the number of units/pulse in
order to keep the output below 100Hz.
5.8.3 Flow Alarm
The Alarm output is enabled by selecting ‘ALARM’ from the digital output configuration
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 alarm dead-band. The Alarm dead-band is
an adjustable buffer zone around the set point which provides hysteresis to the system, and
allows the user to overcome alarm chattering when the flowrate is fluctuating around the set-
point. The dead-band setting is entered as a percentage of the set-point value; e.g. a 5% dead-
band around a 100L/min High Flow Alarm will trigger ON at 100L/min but will not turn OFF
until the flow drops to below 95L/min.
5.9 Analogue Output
The 4-20mA analogue output can be configured anywhere within the operating range of the
connected flowmeter; a 22mA over-range is provided for identification of flows exceeding the
maximum flowrate of the connected flow meter.
The output is configured in flowrate units for the zero point (4mA) and the full scale point
(20mA). The decimal places allowed for the set points are equal to the decimal place
configuration of the Rate display. The 4mA and 20mA points may be entered upside-down, i.e.
a 20mA point lower than the 4mA point. For information on testing or adjustment of the 4-
20mA signal see section 5.10.5 below.
To Next Page
Loading...
General