The BL121 Swimming Pool Controller is a complete system designed for maintaining swimming pool, hot tub, and spa disinfection water quality. The BL121 is available in two configurations. The basic version is the in-line model which allows for direct installation of probe and chemical injection fittings into existing piping. The other version is a panel mounted version with a bypass flow cell. The bypass flow cell allows for calibration and maintenance of the probe without having to shut down the recirculation pump. Additional features of the BL121 include LED indicators for dosing, meter status and service, real-time graph display, programmable alarms, and password protection.
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The controller is available in one of two configurations: an in-line model which allows for direct installation of the probe and chemical injection fittings into existing piping (BL120-10) or a panel mounted system with a bypass flow cell (BL120-20). The bypass flow cell allows for calibration and maintenance of the probe without having to stop the recirculation pump.
The HI1036-1802 is a digital probe that measures pH, ORP, and temperature. This probe also incorporates a potential matching pin. The pin is considered the ?earth ground? connection and is used to prevent ground loop effects from causing erratic readings and damage to the system.


An inline flow switch or a mechanical relay connected to the recirculation pump power source may be connected to the hold input of the BL121. With no flow or when no power is applied to the recirculation pump, the hold circuit disables the dosing pumps. This will prevent any dosing of chemical when there is no movement of water in the system.
The versatile display of the BL121 allows for three screen modes. The LCD can display all three parameters at one time, a 3-second cycle of single parameters, or a real-time plot screen with options for parameter selection, zooming, and log recall.
Hanna controllers allow users to enable or disable the low and high level of alarms for all parameters. When an alarm is activated, all dosing will stop. The alarm system also offers overdosing protection if the value is not corrected within a specified time interval then the meter will go into alarm status.
The BL121 offers multiple LED indicators for status, servicing, and pump operation. The STATUS LED changes color based on operational state; green when setting are in range, yellow when user intervention is required, and red for problems. The SERVICE LED indicates any alarms and process errors experienced by the controller.

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