Tank level is commonly measured with pressure, hydrostatic, ultrasonic, or other level transmitters that provide a 4–20 mA output. By connecting the transmitter to a Microedge current-input data logger, the level can be recorded continuously, converted into engineering units, and monitored locally or remotely.

This Application Note shows a typical system for monitoring tank level using a 4–20 mA transmitter.

1. Application

Consider a storage tank where the liquid level must be monitored continuously.

Instead of checking the tank manually, a 4–20 mA level transmitter measures the liquid level and sends the signal to a data logger.

A typical system consists of:

Level Transmitter → 4–20 mA → Data Logger → PC / Network → Monitoring Software

The system can provide:

• Continuous level recording
• Real-time level display
• Historical graphs
• Engineering-unit conversion
• Remote monitoring
• Alarm monitoring when used with supported software and system configurations

2. Typical Measurement System

A common two-wire 4–20 mA transmitter requires an external DC power supply.

A typical loop is:

24 VDC Power Supply (+)
→ 4–20 mA Level Transmitter
→ Microedge Current Input
→ 24 VDC Power Supply (−)

The transmitter controls the loop current according to the measured level.

For example:

The exact wiring and required power supply should always follow the transmitter manufacturer's specifications.

3. Selecting the Data Logger

Several Microedge data loggers can be used for this application.

LPCB-1

The LPCB-1 SITE-LOG provides seven current-input channels and supports both 4–20 mA and 0–50 mA measurements.

It is suitable when several tanks or multiple current-output sensors need to be monitored from one data logger.

For network access, LPCB-1 can be connected to a Smart-Hub.

PL-C

The PL-C PRECISE-LOG provides eight current-input channels.

It is suitable for multi-channel standalone or USB-connected current monitoring.

If Ethernet or network integration is required, PL-C can be connected through Smart-Hub.

PL-CW

The PL-CW PRECISE-LOG also provides eight current-input channels but includes built-in WiFi.

This makes it useful where the tank monitoring location has access to a wireless network.

PL-CW can communicate directly over the network without requiring a Smart-Hub and can also support Modbus TCP integration.

LPMB-1

The LPMB-1 SITE-LOG provides:

• 3 current-input channels
• 4 voltage-input channels

It is useful when a monitoring system includes a combination of 4–20 mA and voltage-output sensors.

4. Converting 4–20 mA into Tank Level

The data logger measures electrical current, but users normally want to see the actual liquid level.

Suppose the level transmitter is configured for:

• 4 mA = 0 metres
• 20 mA = 5 metres

The level can be calculated using:

where \(I\) is the measured current in mA.

For example, at 12 mA:

Therefore:

5. Displaying Level Directly in SiteView

Microedge SiteView supports custom equations that can convert the measured current directly into engineering units.

Instead of displaying:

12.00 mA

SiteView can display:

2.50 m

The same approach can be used to display:

• metres
• centimetres
• feet
• percentage full
• litres
• gallons

If the relationship between liquid height and tank volume is linear, the conversion can be straightforward.

For tanks with non-linear geometry, a more appropriate conversion equation or calibration relationship may be required.

6. Monitoring Tank Percentage

Sometimes the actual height is less important than the percentage of tank capacity.

For a standard 4–20 mA transmitter representing 0–100%:

Therefore:

• 4 mA = 0%
• 8 mA = 25%
• 12 mA = 50%
• 16 mA = 75%
• 20 mA = 100%

This provides a convenient way to display tank status.

7. Local Monitoring

For a nearby installation, the simplest configuration is:

Level Transmitter → Data Logger → USB → SiteView

SiteView can be used to:

• Configure the data logger
• Download recorded data
• Display measurements
• View graphs
• Apply custom equations
• Analyze historical data

This configuration is appropriate when remote network access is not required.

8. Remote Monitoring with Smart-Hub

USB-based Microedge data loggers can be connected to a Smart-Hub for Ethernet network access.

Typical architecture:

Level Transmitter
→ LPCB-1 / PL-C / LPMB-1
→ Smart-Hub
→ Ethernet Network

Smart-Hub can provide:

• USB Device Server access
• RESTful Web API
• Modbus TCP Gateway

The logger can therefore be accessed by Microedge software or integrated with other systems.

For example:

Tank → LPCB-1 → Smart-Hub → SiteView-Web / Pluto

This allows tank information to be viewed through a browser-based monitoring system.

9. Direct WiFi Monitoring with PL-CW

Where WiFi is available, PL-CW provides a simpler network architecture:

Level Transmitter → PL-CW → WiFi Network

PL-CW can then be accessed by supported Microedge software and network applications.

For industrial integration:

Level Transmitter → PL-CW → WiFi → Modbus TCP → PLC / SCADA

This can be useful when the tank level needs to be incorporated into an existing control or supervisory system.

10. Browser-Based Monitoring

Using SiteView-Web or Pluto, supported remote data loggers can be monitored through a web browser.

Users can view information such as:

• Current tank level
• Historical measurements
• Graphs
• Logger status
• Alarm conditions

This allows monitoring from a PC, tablet, or smartphone connected to the appropriate network.

A typical architecture may be:

Tank Sensor → Data Logger → Network → SiteView-Web / Pluto → Web Browser

11. Alarm Monitoring

Tank-level applications commonly require attention when the liquid reaches a high or low limit.

For example:

• Low level: below 15%
• High level: above 90%

With an appropriate Microedge monitoring configuration, thresholds can be used to identify abnormal conditions and support notification or operator response.

The specific alarm implementation depends on the data logger and software used in the system.

12. Multiple Tanks

A multi-channel data logger can monitor several tanks at the same time.

For example, one PL-CW or PL-C provides up to eight current-input channels:

Tank 1 Transmitter → Channel 1
Tank 2 Transmitter → Channel 2
Tank 3 Transmitter → Channel 3
…
Tank 8 Transmitter → Channel 8

Each channel can use its own conversion equation based on the corresponding transmitter and tank.

This can reduce the amount of hardware required for multi-tank installations.

Example System Configurations

Conclusion

A 4–20 mA level transmitter combined with a Microedge current-input data logger provides a practical way to monitor tank level continuously.

The basic measurement path is:

Level Transmitter → 4–20 mA → Data Logger → Engineering-Unit Conversion → Monitoring System

For simple installations, the logger can record data locally and communicate with SiteView through USB.

For remote applications, Smart-Hub can add Ethernet connectivity to USB-based loggers, while PL-CW provides direct WiFi connectivity. SiteView-Web or Pluto can then provide browser-based monitoring, and Modbus TCP can be used where integration with PLC, HMI, or SCADA systems is required.