Operation and Control
The PCS provides a “home” screen for Master Plant Control. From this screen, the operator can select AUTO, HAND, or OFF for starting and stopping the operation of the WTP. The desired Plant ON level and Plant OFF level as measured in the clearwell are operator adjustable parameters.
Local Control:
Manual or HAND operation requires the operator to select HAND from the Master Plant Control home screen. The following critical alarms shall stop plant operation whether in AUTO or HAND mode:
- A high or high-high level alarm in the clearwell.
Once the clearwell level setpoints are selected, the operator can select HAND Plant control and the WTP will initiate operation, starting each piece of equipment. The PCS controls the raw water pumps selected by the operator. The WTP will remain in operation (ON) until the operator selects Plant OFF, or the PCS initiates shutdown due to a clearwell high level alarm.
If commanded to initiate operation in either AUTO or HAND mode, the PCS shall provide a common FAIL alarm upon individual alarms that prevent equipment start.
PCS Control:
Automatic or AUTO operation requires the operator to select AUTO from the Master Plant Control home screen. The operator must also enter the clearwell level setpoints.
If AUTO is selected along with the desired clearwell level setpoints, the PCS controls the operation of the plant based on clearwell level, which initiates Plant START and Plant STOP, as described in the following table:
Initial Plant Control Settings (Operator Adjustable)
| SETPOINT | ELEV (FT) | ACTION ON RISING LEVEL | ACTION ON FALLING LEVEL |
| STOP PLANT/ HIGH CLEARWELL LEVEL ALARM | 95.00 | 1. STOP PLANT 2. ANNUNCIATE HIGH LEVEL ALARM | – |
| STOP PLANT | 94.50 | 1. STOP PLANT | – |
| START PLANT | 91.50 | – | 1. START PLANT |
| START PLANT/ LOW CLEARWELL LEVEL ALARM | 91.00 | – | 1. START PLANT 2. ANNUNCIATE LOW LEVEL ALARM. |
| LOW, LOW CLEARWELL LEVEL ALARM | 90.50 | – | 1. START PLANT 2. ANNUNCIATE LOW, LOW LEVEL ALARM. |
The PCS controls the number and combination of raw water pumps operating to maintain the WTP Production Rate.
The PCS allows the operator to change the selected raw water pumps and high service pump production rate during operation. The WTP will remain in operation until commanded to stop based on clearwell level and the PCS initiates shutdown. In AUTO mode, the operator can shut down the WTP by switching to OFF mode.
If commanded to initiate operation in either AUTO or HAND mode, the PCS provides a common FAIL alarm upon individual alarms that prevent equipment start.
PCS / HMI Configuration:
- Status Display:
- Plant AUTO / HAND / OFF switch indication
- Clearwell level indication
- Operator Entries:
- Plant AUTO / HAND / OFF switch
- Plant START / STOP switch
- Clearwell Water Level alarm setpoints (high-high, high, low, low-low)
- Clearwell Water Level operational setpoints (start plant, stop plant)
- Historical Trending:
- Plant ON run time (hours)