Overview
For this new rainwater harvesting project, we recommended our client to use a HMI+PLC design. This is because there is an existing Rosemount pressure transmitter that transmits 4-20mA signal to our control panel. Hence, using this signal, we are able to display the water level of the rainwater collection tank on the HMI.
The water level set points can also be easily adjusted on the HMI. There are 3 default set points for this system:
Q3 – 930 (High level, inlet valve closes, drain valve opens)
Q2 – 880 (Filter pump starts)
Q1 – 250 (Low level)
Modification works (3P4W to 3P3W)
Before this, the panel had been designed for a 3 Phase + 1 neutral incoming cable. However, upon site installation, they realised that there is no neutral incoming. This is quite common in some factories and marine sector where they will “save” on the neutral cable since most motors are balanced load.
Hence, the panel had to be brought back to the workshop to be re-wired to suit the site condition. A 415/230V Transformer is added to provide the neutral for our control panel (as our panel lights are all 230V). This is not needed in marine boards where they use 415V for their control circuits.
An earth leakage relay and ZCT with shunt trip coil is used instead of an RCCB. As in this case, an RCCB will cause nuisance tripping if there is no neutral return.
HMI Screens
Site Commissioning (Update)
Rainwater Harvesting Tank
This is a industrial tank re-purposed to be used for collection of rainwater. The collected rainwater will be fed to the cooling tower at the rooftop.
Rosemount Pressure Sensor
This is the Rosemount Pressure sensor (4-20mA) connected to the bottom of the tank, it will sense the water pressure in the tank and determine the water level.