Pulse meter or flow meter, divider,
pulse-responsive pump
Pulse Meter and Pump
The simplest and most common approach is to use a “pulse-responsive” metering pump with a pulse meter. In the LMI line, this would be any of the following model series:
A7 Series, A9 Series*
B7 Series, B9 Series*
C7 Series, C9 Series*
E7 Series
*See the special section on A-, B-, and C-9 pumps
In this approach, the meter generates pulses proportional to the volume of water, and the pump strokes once for each pulse. SeaMetrics fixed pulse rate meters are the M-Series and WP meters.
Connector. The LMI pump requires a connector for external pacing. Any ME meter can be ordered with this connector pre-installed. The LMI connector is ordered by adding the option number -06 to the end of the model number.
Pulse Rate. M-Series meters are ordered with the desired pulse rate preset. The pulse rate can be modified on site, following instructions in the meter manual, but this requires removal of the top meter. It is much more convenient to order the correct rate in advance.
To determine the ideal pulse rate, after selecting the pump (using the guidelines given in the LMI literature) follow these calculations:
The exact rate is not possible using an M-Series meter, but a 1 G/P meter can be used, and the stroke adjustment down to make up the difference. Alternatively, a meter plus divider can be used to set the exact number. (See next section)
Meter, Divider, and Pump
This approach uses an electronic divider to adjust the pulse rate. In this way, the ideal pulse rate can be used, and can also be adjusted as needs change. Also, higher-output flow meters (such as SeaMetrics IP paddlewheel series) can be used.
There are two kinds of dividers, external and internal. All A9-,
B9-, C9-, and E9- pumps have built-in microcontroller-based dividers,
which are programmed at the pump. For other pulse-responsive pumps,
the SeaMetrics PD10 serves the same function externally. The FT415
& FT420 flow computers can also be used. They add display of rate
and total flow to a programmable divider function.
A divider counts pulses and strokes the pump once when the preset
"divider factor" is reached. The meter selected should have a higher
pulse rate than the rate needed for the pump, to allow adjustment
of the divider number.
Meter, Counter/Timer, and Pump
This approach uses a simple on/off pump, and amay be the most economical approach is a higher-volume chemical output is needed. To match chemical feed to flow, an additional control unit is used. This unit, a counter/timer, counts pulses from the meter. When a preset number of pulses has been counted, the timer turns on the metering pump and keeps it on for a set amount of time. Since the result is an on-off chemical flow, or “slug feed”, there must be enough mixing capacity in the system to even out chemical concentration before the point of first use. One popular application is the feeding of treatment chemicals into a cooling tower system. The cooling tower tank typically provides plenty of opportunity for mixing before cooling water enters the piping system.
The SeaMetrics single counter/timer is designated the PT34. A double
counter/timer, model PT35 can be used to control two different pumps
or one pump and one valve.
Flow Meter and Pump on
4-20 mA Current Loop
In this system, a standard 4-20 mA analog signal is transmitted by the flow meter, and the pump follows this signal. Almost all SeaMetrics flow meters can
be equipped to transmit current loop signals proportional to the flow (4 milliamps at zero flow, rising to 20 milliamps at maximum flow). The following LMI pump models are equipped to respond to this signal:
A9, B9, C9, H9 Series
L4, L8
Programmable Metering Pumps -
A9, B9, C9
The capabilities of these LMI pumps are expanded by the addition of microprocessor control. The main advantage for use with flow meters is increased flexibility. A built-in divider makes it possible to connect an IP or TX flow meter directly to the pump, powered by the pump's 12VDC power supply. Alternatively, a flow meter with 4-20 mA output can be connected using the 4-20 mA feature. If using an LMI pump with an IP, TX, or SPX flow meter, it is necessary to change the de-bounce setting (minimum input pulse width) from the factory setting of 15 down to 0 or 1, due to the short pulses these flow meters produce, particularly at high flow rates.
