28
rate mode is selected in block o1. In the example above, the number of points
chosen in block o4 would be four. The more points that are chosen, the closer the
graph of the straight lines between points gets to the curve, and the more accurate
the flow rate and totalization readings become.
If linearization is chosen in block o1, the number of points must be selected in block
04.
Some flowmeters produce output signals where the square root of the output ampli-
tude is directly proportional to flow rate. The differential pressure meter is the classic
example of this. In this case, if the flow rate doubles, the output signal increases by
a factor of four; if the flow rate triples, the output signal increases by a factor of nine,
etc. The graph of output signal to flow rate would look like this:
2
0
25
50
100
Flow Rate (GPM)
Output
Signal
(volts)
cutoff
For these flowmeters, the square root extraction rate mode should be selected in
block o1. When this is done, the cutoff value must be entered into block o2 and the
constant must be entered into block o3.
The cutoff value is the voltage or current that the meter puts out when the flow rate is
zero. This can be read by a meter.
The constant value can be calculated by the following formula:
Constant =
Flow Rate
Output - Cutoff
,
where Output is the voltage or current reading at a particular Flow Rate value.
Example: a flowmeter puts out 0.15V at a flow rate of zero GPM (cutoff) and 6.40V at
a rate of 100 GPM (Flow Rate).
Constant =
100
6.40 - 0.15
= 40
PROGRAMMING cont.
