What is a water level logger and what is it used for?

Written by Lincoln Jordan

We break down the different parts of water level loggers and what they are used for as well as tips and tricks to read water level loggers.

Sensors:

What is a sensor

A sensor is a device or element designed to detect and measure various physical properties, responding to changes by recording, indicating, or triggering a specific action (Figure 1). These components find applications across various fields, including automotive, aerospace, medical, and environmental monitoring.

 

Figure 1 Different sensor types.

 

Transducers in Water Level Data Loggers

Water level data loggers utilise pressure sensors (transducers) to track fluctuations in water levels (Figure 2). These sensors employ the piezoelectric effect of materials to measure such variations accurately.

 

Figure 2: Water Level pressure sensor.

 

How does the Piezoelectric Transducers Work?

Piezoelectric transducers operate based on the piezoelectric effect, which generates an electric charge when certain materials are subjected to mechanical stress.

Piezoelectric transducers operate through a series of steps involving piezoelectric material properties. These sensors are constructed using a piezoelectric material as their core component. When pressure is applied to the sensor, this material undergoes deformation, experiencing mechanical stress as a result.

This mechanical stress triggers the material’s inherent piezoelectric properties, causing it to generate an electric charge. A voltage is produced across the piezoelectric material, which is then detected by electrodes attached to its surface. This voltage output serves as the signal indicative of the applied pressure. The magnitude of the voltage output is directly proportional to the level of pressure applied (Figure 3).

The sensor must be precisely calibrated to interpret the signal and derive meaningful pressure measurements. Calibration involves accounting for various factors, including the specific properties of the piezoelectric material used in the sensor’s construction. Through meticulous calibration and consideration of these material properties, the voltage reading obtained from the sensor can be translated into an accurate representation of the pressure or submergence in water.

 

Figure 3: Diagram of a transducer.

 

Logger

What is a logger?

A logger typically refers to a program, system, or device that records or logs events, activities, or data for various purposes. Logging is the process of systematically recording information about events that occur in a system, application, or device.

 

How does a water level datalogger work?

The data logger automatically captures signals from the transducer at regular intervals, typically in the form of time-stamped measurements. These readings are then stored internally within the logger, usually in non-volatile memory, ensuring data retention even in the event of power loss. Users can retrieve the recorded data by directly connecting to the device or through remote access via wireless communication technologies such as Bluetooth, Wi-Fi, or cellular networks. 

 

Once the data is accessed, specialised software or tools can be used for analysis, converting the pressure readings into water level measurements over time. Two widely used water level data loggers in South Africa are the Solinst Levelogger series and Van Walt’s LevelSCOUT series (Figure 4). 

 

Figure 4: Picture of water level dataloggers. Left Solinst Levelogger 5 and right Van Walt LevelSCOUT 2X.

 

What are water level loggers, and where are they used?

Water level loggers are specialised devices designed to measure and record water levels in various water bodies, including wells, boreholes, rivers, lakes, and groundwater aquifers. Equipped with pressure-based sensors, these loggers detect changes in water pressure caused by fluctuations in water depth, capturing data at regular intervals.

This information is crucial for understanding and monitoring water resources, aiding in tasks such as groundwater management, environmental conservation, flood forecasting, infrastructure maintenance, and scientific research.

 

Why is a water level logger better than taking hand water level readings?

A water level logger surpasses hand water level readings due to its automation, accuracy, continuous monitoring capabilities, remote accessibility, and reduced susceptibility to environmental factors. By automating the measurement process, water level loggers eliminate human error and provide precise and consistent data over time.

Their ability to continuously monitor water levels allows for comprehensive data collection, capturing fluctuations and trends that may be missed with periodic hand readings. Additionally, remote accessibility enables real-time monitoring from a distance, facilitating prompt responses to changing conditions. Overall, water level loggers offer a more efficient, reliable, and comprehensive approach to water level monitoring compared to manual readings.

 

Vented and Unvented datalogger

 

Vented dataloggers

Vented data loggers use transducers that are connected to the atmosphere through a vented communication cable (Figure 5). This cable includes a small vent tube running along its length from the surface to behind the pressure transducer. The vent tube serves as a pathway for changes in barometric pressure at the surface. It allows the barometric pressure affecting the water column to be balanced out by the pressure transmitted through the tube. This setup automatically adjusts the data for both barometric effects and changes in altitude. The main drawback of using a vented datalogger is that the logger functions better at shallower depths. 

 

Figure 5: Diagram of a vented cable.

Unvented (Absolute) dataloggers

The unvented datalogger transducers are sealed, meaning they measure all the pressure they experience, including water pressure (hydraulic head) and air pressure acting on the water’s surface (barometric or atmospheric pressure). The data must be adjusted for barometric effects to get accurate hydraulic head measurements. The simplest way to do this is by using a second data logger, known as a barologger, which records air pressure only. The barologger is installed above the water near the surface. The software that is used to read the datalogger will normally have a function where the unvented datalogger file is automatically compensated to the barologger file. 

Figure 6: Levelogger and Barologger installation.

 

In the example below (Figure 7), the graph shows both the barometrically compensated and uncompensated data. It is clear from the graph that the barometric compensation normally reduces noise in the water level data. 

 

Figure 7: Graph of compensated and uncompensated water level data.

 

Datalogger installation depth

To ensure accurate readings, water level dataloggers need to be installed within a specific submergence range below the water surface. Dataloggers with high-pressure range ratings may be less accurate when installed in shallower water depths, and dataloggers with lower pressure ratings will be inaccurate, read a maxed-out value or might fail at deeper submergence. 

 

Solinst Levelogger series uses the maximum submergence depth as part of the model name. For example, the M5 datalogger has a maximum submergence depth of 5 meters for accurate measurements (Table 1). The logger will still record up to double the amount of submergence, but these readings are less accurate. 

Table 1: Solinst Levelogger pressure ratings.

Model Pressure Range Maximum Submergence Depth for Accuracy Maximum Operating Submergence
M5 Up to 5 meters 5 meters 10 meters
M10 Up to 10 meters 10 meters 20 meters 
M20 Up to 20 meters 20 meters 40 meters 
M30 Up to 30 meters 30 meters 60 meters 
M100 Up to 100 meters 100 meters 200 meters 
M200 Up to 200 meters 200 meters 400 meters 

 

The Van Walt’s LevelSCOUT series will only read accurate values up to the maximum submergence depth (Table 2). Also, if the maximum operation submergence is exceeded, a constant maximum value that does not represent the true submergence will be recorded (Figure 8). 

Table 2: Van Walt LevelSCOUT pressure ratings

Pressure Range Maximum Submergence Depth for Accuracy Maximum Operating Submergence
Up to 10 meters 10 meters 11 meters
Up to 24 meters 24 meters 22 meters 
Up to 59 meters 59 meters 65 meters 
Up to 200 meters 200 meters 220 meters 

 

 

Figure 8: Van Walt logger installed to deep

 

Tips and tricks for reading dataloggers

 

Reading Solinst data loggers 

The Solinst Levelogger can be downloaded through various devices like a computer, phone, USB or a Solinst Readout Unit (SRU) device. The adapter connected to the loggers is normally an Optical reader of a PC interface reader. 

 

Reading the Levelogger Edge

The Levelogger Edge has been discontinued and replaced with the Levelogger 5, but many of the Edge loggers are still installed at monitoring points (Figure 9). The Edge levelogger transfers infrared signals through the optical eye.

 

To connect the datalogger successfully, these optical eyes must be inspected and dried before inserting the logger into the relevant adapter. If one of the two optical eyes is black, this is normally an indication that the logger might not connect. The logger eye can be dried with a rolled-up piece of paper, cotton swab or compressed air. Do not try to blow the optical eyes dry because this will cause damp water to precipitate on the eyes and can cause the logger not to connect. If the logger still does not connect, it is recommended to leave it in the sun or let the logger’s eyes dry overnight and then try to reconnect the logger.

Figure 9: Solinst Levelogger Edge.

Reading the Levelogger 5

The Level 5 levelogger is Solinst’s newest datalogger version (Figure 10). Significant physical differences exist between the Levelogger 5 Series and the Levelogger Edge. The Level 5 levelogger only has a single Optical eye with a larger surface area. The Level 5 levelogger is faster and connects more easily to the different reading devices. It is still recommended that the logger’s eye be dried before connecting to the adapter.

Figure 10: Solinst Levelogger 5.

Preferred reading device

The Solinst levelogger can be downloaded using various devices, but certain limiting factors exist. The Solinst DataGrabber uses a USB drive to download the logger (Figure 11). This method does not allow you to view downloaded files, view the logger details or reset/program the logger from this device.

Figure 11: Solinst DataGrabber 5.

 The Solinst Levelogger App Interface lets you download and view the logger file on your phone, but you cannot reset/program the logger (Figure 12). The Bluetooth function of this device does not always connect seamlessly, which can waste time in the field. 

Figure 12: Solinst Levelogger App Interface.

The SRU connects and downloads the logger very quickly, but you cannot view the downloaded data from the device, and you can also not reset/program the logger (Figure 13). 

Figure 13: Sonlist Readout Unit. 

Using your computer is advantageous because the downloaded data can be reviewed on your computer, the logger can be reset, and the battery level of the logger can be checked, but taking your computer/laptop to the field is not always convenient (Figure 14). 

 

Figure 14: Laptop and Desktop reader 5.

Reading Van Walt data loggers 

The Van Walt LevelSCOUT series can only be read by a computer and the appropriate RS485 or SDI 12 Adapter (Figure 15). The LevelSCOUT logger connects very consistently with the Aqua4Plus software. It is important to refresh the software each time a new logger is connected because if this is not done, it could cause the software to identify the logger wrongly. 

Figure 15: Diagram of LevelSCOUT connection to a laptop. 

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