15
WIRING cont.
Programming Considerations for Flowmeter Input and DIP Switch Definitions
The inhibit input will normally not be used. The count inhibit function means that the
counter will ignore flowmeter pulses when inhibit is active. This is handy at some
times, such as when the system is being purged. However, experience has shown
that most users do not care to use this function. Inhibit inputs on counters around
the world are aware of this fact; because of it, inhibit inputs generally suffer from lack
of self-esteem. Inhibit inputs are the original Maytag
®
repairman. Durant is a sensi-
tive, caring counter manufacturer that has decided to do something about this. The
inhibit input on the Eclipse is programmable (in block F1, page 26) to either do its
traditional inhibit duty, or to select between two pre-loaded K factors. This opens up
a number of application possibilities, some bizarre, some simply clever. If one K
factor is the number of pulses per gallon and the other K factor is the number of
pulses per liter, the user can go from counting in gallons to counting in liters and vice
versa simply by throwing a switch. Gallons to pounds conversion is another likely
scenario.
Setting the DIP switches can be an adventure since there are a wide variety of
flowmeter types and there is no standard output pulse signal. Furthermore, signal
conditioning devices, such as flow transmitters, may change the electrical charac-
teristics of the signal. The most common flow signal is a differential, AC voltage
generated by a paddlewheel flowmeter. This is a two wire signal, and the output
frequency can easily exceed 200 Hz. Mag pickups are sink and source, so don’t
worry about DIP switch 1, just turn 2 OFF and 3 ON. Contact outputs, such as reed
switches, are much less common. They can be set up as sink, as shown in the
diagram, or source. Since the diagram shows how to wire them as sinking sensors,
use that method. Contact inputs will always be low speed, so switch 2 is ON.
Transistor output signals are generally three wire, since the transmitter usually
requires DC operating power. The Eclipse puts out 12 VDC for these types of sen-
sors. Transistors are either NPN or PNP. NPN outputs are sinking outputs; they
provide the path to ground. PNP outputs are sourcing; they provide the path to posi-
tive. These signals are considered “single ended” because they are referenced to
common (ground). They can easily be high frequency signals. Switches 2 and 3
should be OFF, and switch 1 is OFF for PNP, and ON for NPN.
