As described previously, most plant processes can be operated in a manual (HAND) or an automatic (AUTO) mode as described individually in Chapters 3 and 4.
The Glasgow WTP can be operated in an automatic mode or manual mode for PLANT START and PLANT STOP. Hand switches for each piece of equipment will typically be left in the AUTO position, unless the equipment is removed from service for any reason or is operated in HAND mode for purposes of calibration, testing, etc.
In automatic mode, equipment in most unit processes operates when a PLANT START signal is initiated. Variable speed pumps and feeders at the Glasgow WTP typically operate at speeds set by flow or pace controllers. These flow controllers (for flow rate control) or pace controllers (for chemical pacing) receive flow rate or chemical concentration signals and vary the motor speeds for the corresponding pump or feeder to meet the set points entered at the HMI.