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5.8 Digital Output
The digital output function is configurable for either a pulse output according to totalised
flow, or an alarm output according to flowrate. The pulse output can be configured for an
unscaled pulse or a scaled pulse, and the alarm can be configured for notification of high
flowrates, low flowrates, or a combination of both.
5.8.1 Un-Scaled Pulse
The unscaled pulse output, also commonly referred to as a ‘repeater pulse’, is enabled by
selecting ‘UNSCALED’ in the digital output configuration menu.
5.8.2 Scaled Pulse
The scaled pulse output is enabled by selecting ‘SCALED’ in the digital output menu.
Configuration of this output is accomplished by entering the number of pulses per unit; e.g. 10
pulses/Litre, 1 Pulse/Gallon, etc.
The user may configure this setting in the range of 999.99 – 0.01 pulses per unit, however it is
not possible to output a higher resolution than that of the input signal. For example, if your
flowmeter output resolution is 100 pulses per Litre, then the scaled pulse output must be
configured for less than 100 pulses per Litre.
The frequency of the Scaled Pulse Output signal automatically adjusts according to the input
frequency and the scale factor, up to a maximum limit of 100Hz. If it is necessary for the scaled
pulse output to operate at greater than 100Hz the instrument will 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 decrease the number of pulses per unit,
in order to keep the output below 100Hz.
The pulse width of the Scaled Pulse output is fixed at 300ms for output frequencies below
1.67Hz, however once above 1.67Hz the instrument adjusts the pulse width according to the
frequency to give a 50:50 duty cycle up to the maximum output frequency of 100Hz.
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