Yokogawa 212 Heat Calculator - Manual (Page 27)

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:
frequency (Hz) =
flow rate x K-factor
time base
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 is
63, then the cut-off frequency:
f =
50 x 63
3600
= 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.
Operation 25