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Section 4 Installation
4.1 Sample Point Selection Guidelines
General Considerations
The sample must be taken at a point after the chlorine has been thoroughly mixed and has had time
to react completely with the process water. A sample point that is too close to the chorine injection
point will deliver a sample that is not mixed adequately or has not had sufficient time to complete the
chemical reaction, thereby producing inaccurate readings. The supplied 3-ft long sample tubing may
be cut to minimize distance.
The analyzer requires a continuous sample flow 30 liters per hour (8 GPH) at no more than
atmospheric 15 psig pressure and a drain for sample waste. A pressure regulator and flow control
valve upstream of the sample flow cell inlet is required.
Considerations for Control:
For residual control purposes the lag time between chemical injection and detection by the analyzer
should be as short as possible, no more than 10 minutes. Longer lag times will result in a continuous
cycle of over and under feeding the disinfectant.
Sample Line
The sample line should be run with 3/8” diameter rigid PVC tubing to minimize lag time between the
process and analyzer. If a long sample line run is unavoidable, increase the flow rate to the analyzer
to about 10-ft/sec. to reduce the sample transport time and then throttle down..
When connecting the sample line into a larger process pipe, use corrosion resistant fittings only. The
sample tap should be installed into the center of the pipe from either the top or side to minimize the
chance of introducing air bubbles or sediment into the analyzer.
A submersible pump is required to sample from a reservoir or basin.
Filters are not recommended as the trapped material will develop a chlorine demand, resulting in the
analyzer measuring a residual that is lower than is present in the process. Some applications may
require a PVC flushing wye strainer to remove particulates from the sample.
In low residual applications biological growth can occur in the sample line, which will reduce the
residual before it reaches the analyzer. Regular disinfection is required in such applications.
Sample Flow Consistency
Consistent flow and pressure is critical to accurate measurement. A change in flow rate during
operation of a calibrated analyzer will require a recalibration of the analyzer.
