212-M-V2.1
Operation 25
3.4 FREQUENCY CUT-OFF
A frequency cut-off can be programmed to prevent registering very low
flow signals which may be the result of spurious pulses or a drift in the
zero point of a flowmeter, such as magnetic flowmeter.
Input frequencies at or below the cut-off are not registered and no flow is
totalised.
The relationship between the flow rate at cut-off and the frequency is:
where time base = 60 if the flow rate is in units/min and 3600
if the flow rate is in units/hour.
flow rate = flow rate at the cut-off.
K-factor = pulses per unit for the flowmeter.
For example, if the required cut-off is 50 l/h and the K-factor for the
flowmeter I 63, then the cut-off frequency:
= 0.88Hz
Generally, at frequencies above 0.25Hz, the cut-off is left at the default value
of 0.25Hz. However, some water meters produce relatively low frequencies
and the cut-off may need to be programmed to a frequency less than 0.25Hz.
Note: Be careful when setting low cut-off values below 0.25Hz, since the
display update time on the flow rate and power will become long. For
example, if the cut-off is set to 0.01Hz, the instrument will continue to display
the flow rate for 100 seconds, if the signal stops. This is because the time
interval between the signal at 0.01Hz is 100 seconds and the Model 212 must
wait this long before it can determine that the flow has actually stopped.
base
time
factor
-Kxrateflow
(Hz)frequency =
3600
63x50
f =
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