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Continuous Level Control for Pumping Stations

Antique pumping stationIn addition to the various types of point level sensors for pumping stations, a more advanced approach is growing in popularity. Many businesses and municipalities are using continuous level sensors. Some popular sensors for continuous level measurement are submersible pressure transducers, ultrasonic and radar sensors, and level probes.

Switching to a continuous level sensors is a step toward modernizing pumping stations. Modern equipment that increases efficiency and saves money works much better with continuous level sensors, creating several advantages.

Let’s compare the differences between continuous and point level sensors:

1) One vs Many

Point level sensors take a measurement at preset levels, simply notifying the operator when that level has been reached. There is typically only one level that can be measured per sensor, though the KA float switch series has up to four levels.

A continuous level sensor, on the other hand, can measure many points within the range or span of the sensor. How many points in a given range? The resolution of a sensor is generally defined as the distance between two separate points that a sensor can measure. For example, if a sensor has ¼” resolution it can measure in increments of ¼”.

2) Outputs and Options

Point level sensors generally have outputs, which are electrical contacts that open or close. Continuous level sensors provide a variety of outputs such as voltage, current, or fieldbus outputs. Common voltage outputs are 0-5VDC, 0-10VDC and current outputs are generally 0-20mA and 4-20mA. Fieldbus connections such as Hart, Modbus and others allow sensors to be read and sometimes configured by a PC or some type or process controller.

When using analog or continuous level sensors, a controller is almost always needed. These controllers can be proprietary to the sensor or can be fully configurable with software. Proprietary controllers are pre-programmed to function in a specific process such as duplex alternating pump control. Open controllers such as Programmable Logic Controllers, or PLCs, allow programmers to adapt to a wide range of processes. A further discussion of controllers is beyond the scope of this article and may be discussed in greater detail at a later date.

What are the major advantages of continuous level sensors?

3D lift-station cut away illustrationEnergy Savings, Reduced Maintenance, and ROI

Traditionally, pumping systems such as lead/lag float control pumps are turned 100% on or off at specific tank levels. With a continuous sensors, rather than cycling pumps on and off, the level can be maintained by controlling the speed of the pump based on level.

This approach has been widely used in building ventilation systems due to the energy savings, and is catching on in the pumping industry. The ROI on switching to a variable speed drive pump with a continuous level sensor can often be as little as 1 year, depending on the application.

Hard Data and Better Planning

When continuous level sensors are used, inventory can be monitored. Simply by knowing the dimensions of the tank or well, one can calculate volume. Additionally, measuring the volume in time intervals allows flow measurements to be estimated. This provides several benefits including, accurate usage information, pump efficiency data, maintenance cycle planning, and others.

Essentially, with continuous level sensors, you can do and know more. For pumping stations, controlling the speed of pumps is the main application. This is one of the few applications where ROI is well understood and can be calculated based on a few details. We’ll follow this article up with a few posts explaining the continuous level sensors used commonly in lift stations.

Do you use point level sensors, or continuous level sensors? Have you been in one camp and switched to the other? If so, why? Tell us your thoughts on why one is better than the other.

If you have questions, and would like to speak with an application engineer, give us a call at 888-753-7300, or stop by our contact us form.

Looking for continuous, customizable readings from your level sensors? APG offers Modbus outputs on every line of continuous level sensor:

Browse APG Modbus Sensors and Controllers

Images: top-right, old pumping station. bottom-left, duplex lift station by Romtec Utilities - used with permission.

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