Go deeper into the Lift Station Guardian controls with a look at its instrumentation, control schema, and special features.
The bar chart below shows the instrumentation and setpoints described in this guide.
Bar Chart Legend | ||
High Float Level (PLC Control) Pump Start Level Setpoint (Tagger Control) Current Level (Tagger Control) |
| Pump Stop Level Setpoint (Tagger Control) Low Float Level (PLC Control) |
Instrumentation
Level Transducer
A level transducer is installed as close as possible to the bottom of the well. It measures the hydrostatic head pressure (pressure from the weight of water column above its sensor).
Analog output from this transducer gives the level of the well, indicated by a black arrow on the chart. When the DPO is in Auto Mode (i.e., the DPO HOA, Float Override, and Local HOA are all toggled to “Auto”), the Lift Station Guardian is using the transducer output to control operation of the pumps based on their start/stop levels.
Floats
The floats are mercury-activated, narrow-angle control switches that automatically turn pumps on or off based on the water level inside the well. These tilt switches use a small amount of mercury to open or close a circuit to operate or shut off pumps.
Lift Station Guardian uses the following control switch configuration:
High level configuration (normally open) – when the water level reaches the high level setpoint, the float switch tilts to close the circuit, which tells all available pumps to start.
Low level configuration (normally open) – when the water level reaches the low level setpoint, the float switch tilts to close the circuit, which stops the pump(s).
Click here for more on level sensing instrumentation: https://romtecutilities.com/understanding-level-sensing
Critical Setpoints
Start/Stop
The start level is shown to the left of the bar graph, in blue. The stop level is shown to the right of the bar graph, in gray. These start/stop setpoints are typically set to maximize the range of operation between the floats.
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Note: Heritage Lift Station Guardian installations have individual pump start/stop levels which are set during commissioning. |
High/Low
These levels are determined during commissioning and are confirmed with each Float Test. Wet well high and low float levels are indicated by orange arrows on the bar chart.
Control Hierarchy for Operation
The Lift Station Guardian is designed for the Tagger to control operation of the lift station pumps, but it also provides for PLC and local HOA operation. These functions are described in this section.
Tagger in Control
For the Tagger to be in control, it must be online, and the following must be true:
DPO HOA must be in Auto,
FloatOverride in Auto
HOA (Local) in Auto
When these prerequisites are met, the Lift Station Guardian will operate by the start/stop levels shown on the tank bar graph.
This graphic shows an example of the pump control tile when these criteria are met. These conditions are visible on the Lift Station’s Overview Page in the User Interface.
PLC Control
Second, if something causes Tagger Control to be unable to operate the station (“e.g. the level sensor fails), the PLC will operate the Lift Station by physical floats. It will run all available pumps to do so. Performing regular float tests ensures that this level of protection is available in the event your site needs to run in PLC Control for a time.
Local Control (Human in the Loop)
In an emergency or in a maintenance situation, operators may use the physical HOA, which overrides both the Tagger and PLC control to run pumps as needed.
Maintenance Features
Float Test
This feature allows the well to fill up until it locates the high float. This float level is then logged, and the pumps drain the well until the low float is located.
Users can set timeouts for how long they wish to allow the Lift Station Guardian to search for each float as well as a maximum height the Float Test may reach when searching for the high float. If any of these conditions are exceeded, the Float Test will exit, an alarm will be sent with details as to why, and normal operation will resume.
Pump Snore
The pump snore setting establishes a period of time to run the pumps once the low float level has been reached. This feature allows lift station operators to bring the surface level of the well to the pump inlet, clearing floatable material.
Force Main Scour
The force main scour uses a flow setpoint to establish a high enough velocity in the force main to convey solids down the line, protecting from capacity-reducing build up.
Odor Control
This feature is especially helpful for lift stations operated on an intermittent basis, as it can be used to ensure the lift station pumps are run on some scheduled frequency. Doing so helps prevent the wet well from going septic, reducing unnecessary odor.
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