We’ll cover monitoring in this section and dosing in the following section.
A typical automatic monitoring system comprises a control unit connected to probes that are being supplied with a representative sample of pool water via a sample line taken from the circulation pipework in the plant room.
These probes are constantly monitoring the levels of free chlorine and pH, and are electrically linked to pumps that turn on or off according to the readings from the probes and the parameters that have been pre-programmed into the control unit.
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This video will take you through how automatic dosing works and also talks about some mistakes that often get made when calibrating sensors.
On a monthly frequency (or according to the manufacturers information), the probes should be cleaned and calibrated. As there is a variety of manufacturers, makes and models of automatic monitoring equipment the method for preforming these tasks will vary from one system to another.
Automatic monitoring systems vary in their levels of sophistication. Some are fairly simple: once the chemical pumps’ stroke rate and speed have been set, pumping is activated/deactivated according to the difference between the programmed set-point and the readings obtained by the monitoring equipment.
At the other end of the spectrum, there are controllers that are programmed to predict its response to readings in different circumstances and adjust accordingly in order to prevent under or over dosing, i.e. they are ‘self-tuning’. They can also be connected to computer software to enable better communication in addition to being able to monitor and adjust from anywhere.
Systems also vary in their requirements for cleaning and/or calibration. Some systems will need neither as they are self-cleaning. Refer to the manufacturer’s instructions to find out what type of on-going maintenance your system requires. If it does need to be cleaned and/or calibrated by the user, this usually involves isolating the incoming feed, disconnecting the leads from the control unit to the probes, unscrewing the probes and either dipping them into, or wiping them with a probe cleaning solution.
If calibration is being done at the same time, this usually involves navigating into the appropriate menu screen on the control unit and following the step-by-step instructions. For disinfectant calibration, a sample of pool water is taken from the sample line (not the swimming pool itself) and a free chlorine test is carried out using a DPD 1 tablet in the usual way. The control unit reading is then overwritten with the reading obtained from the DPD 1 test using the on-screen menus.
For pH calibration, the probe is dipped into a solution with a known pH value (supplied by the manufacturers of the system) and then dipped into another solution with either a higher or lower pH value than the first solution. As with chlorine calibration, the operator is required to follow the manufacturer’s instructions specific to the type of equipment and follow the on-screen instructions carefully. It is recommended that pool plant operators request that the service engineers provide them with a tutorial on the automatic control unit during one of their service visits. It is worth remembering that most probes require replacement on an annual frequency.
Unless the system is very old, it should be possible to download the User Manual PDF for the system in use at your facility (we’ve included a few below). These manuals will include a step-by-step procedure to follow in order to clean and calibrate the probes.