8
However, if the new unit selection results in a value which cannot be displayed it will be set to
zero. For example, if display units are changed from Litres to Millilitres and the total has a
value of 1000L this will be zeroed, as there is not enough display digits for a value of
1,000,000mL.
Pressing the Reset key and holding for a period of 3 seconds will reset the total to zero.
2.3.2 Accumulated Total
The accumulated total is displayed on the bottom display line, it can be selected by pressing
the Display key. The accumulated total is always displayed in the same engineering units as
the resettable total.
The accumulated total display can only be reset to zero by accessing the programming menu,
see section 7, or via USB on a Windows PC. To prevent resetting of the accumulated total the
user can use the PIN Protection setting, which can be enabled in the programming menu or via
USB on a Windows PC.
2.3.3 Instantaneous Flow Rate Display
The instantaneous flow rate display is displayed on the bottom display line, it can be selected
by pressing the Display key.
The update frequency of the flow rate display is influenced by two parameters: the update
frequency of the display (2Hz on battery power, 8Hz on external DC), and the ‘Rate Calculation
Pulses’ parameter. If the update frequency of the flow rate is too slow, consider reducing the
number of pulses for the rate calculation. Conversely if it is required to stabilise an erratic flow
rate display, increasing the ‘Rate Calculation Pulses’ parameter will achieve this.
Other parameters which influence the calculated flow rate value are the ‘Filter’ setting, and
the ‘Low Frequency Cut-Off’ setting. Increasing the ‘Filter’ value will smooth out rapid changes
in the flow rate to maintain a steady display, however in systems where fast changes in the
flowrate must be displayed the ‘Filter’ parameter should be minimised.
The minimum input frequency requirement for a flow rate display is 0.1Hz, this is also the
default setting. With input frequencies below the Low Frequency Cut-Off the RT40 will not be
able to display an instantaneous flow rate. Note that Totalisation is not affected by the Low
Frequency Cut-off parameter.
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