Analytical Technology Inc. (ATi) has introduced a new monitoring system for residual chlorine in municipal water treatment systems. The Q45H Residual Chlorine Monitor is available in two versions, a free chlorine monitor for potable water, and a combined chlorine monitor ideally suited for chloraminated water.
Traditional on-line colorimetric and most amperometric monitors require the addition of chemical reagents to detect residual chlorine. These reagents are pumped to a reactor vessel where the chlorine species are converted to a measurable form. This type of chemical addition system often requires a considerable maintenance effort to keep the system operating. Not only must the chemicals be replenished frequently, but as the motors and pump assemblies wear out, they become additional maintenance concerns. The process water is also altered by the addition of the chemicals, which creates wastewater that must be discarded.
The basic sensing element used in the Q45H Residual Chlorine Monitor is a polarographic membrane sensor which measures chlorine directly. This type of measurement does not require the addition of chemical reagents, so there are no moving parts that need to be maintained. The process water simply flows past the sensor and directly to drain, with the flow rate and pressure across the sensor controlled by a constant head flow cell assembly. The chlorine measurement does not alter the sample, so the water flow can return to the system, if desired.
For many free chlorine applications, the pH level in the process water is relatively stable, so the standard monitor and sensor are all that is needed. However, when the pH of the water stream varies regularly, a significant shift in measurable free chlorine concentration occurs. With the simple addition of an optional pH sensor, the Q45H will automatically correct for these changes, maintaining an accurate free chlorine measurement.
The pH sensor option also provides a second analog output that can be assigned to pH, converting the chlorine monitor into a two parameter system, providing isolated 4-20 mA outputs for both chlorine and pH. The pH sensor option is available with either the free chlorine or the combined chlorine monitors.
A standard feature of the Q45H is the PID control function. Control setpoint and variables for Proportional, Integral, and Derivative are entered using the front panel push buttons. The isolated 4-20 mA output can then be used as the control input to any metering pump with analog input capability.
