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Enabling better global research outcomes in soil, plant & environmental monitoring.

VSL Voltage Sensor Logger

The Voltage Sensor Logger (VSL) is a stand-alone logging instrument for the measurement of any sensor with an analogue voltage output.

The VSL can support up to five differential or up to ten single ended sensors with the same voltage input requirements.

The VSL is a fully self-contained unit requiring power input from a 22W solar panel (field applications) or 24V power supply (laboratory applications). Communication is via a USB port or wireless connectivity. The VSL is IP-65 rated and has a Windows and Mac compatible GUI for complete logging solutions including look-up tables, scripts and sensor calibration capabilities.

The VSL is ideally used in combination with the ICT International range of soil, plant and environmental sensors. To custom design a VSL to your sensor contact ICT International for a complete solution.

Instrument Logging

Analogue Channels 5 differential or 10 single ended
Resolution 0.00001V—24-Bit
Accuracy 0.001V
Minimum Logging Interval 1 second
Delayed Start Suspend Logging, Customised Intervals
Sampling Frequency 10Hz


Communications USB, Wireless Radio Frequency 2.4 GHz
Data Storage MicroSD Card, SD, SDHC & SDXC Compatible (FAT32 format)
Software Compatibility Windows 7, 8 & 8.1, 10. Mac OS X
Data Compatibility FAT32 compatible for direct exchange of SD card with any Windows PC
Data File Format Comma Separated Values (CSV) for compatibility with all software programs
Memory Capacity Up to 16GB, 4GB microSD card included.

Operating Conditions

Temperature Range -40°C to +80°C
R/H Range 0-100%
Upgradeable User Upgradeable firmware using USB boot strap loader function


Internal Battery Specifications
960mAh Lithium Polymer, 4.20 Volts fully charged
External Power Requirements
Bus Power 8-30 Volts DC, non-polarised, current draw is 190mA maximum at 17 volts per logger
USB Power 5 Volts DC
Internal Charge Rate
Bus Power 60mA – 200mA Variable internal charge rate, maximum charge rate of 200mA active when the external voltage rises above 16 Volts DC
USB Power 100mA fixed charge rate
Internal Power Management
Fully Charged Battery 4.20 Volts
Low Power Mode 3.60 Volts – Instrument ceases to take measurements
Discharged Battery 2.90 Volts – Instrument automatically switches off at and below this voltage when no external power connected.
Battery Life varies
Example A: With a recommended solar panel and/or recommended power source connected, operation can be continuous.
Example B: Power consumption is dependent on number and type of sensors connected, frequency of measurement and measurement duration

How It Works

Sensor Compatibility:

There are two levels of compatibility:

  1. Single ended and differential compatibility
  2. Voltage excitation compatibility

Single ended sensors use two conductors: one ground and one signal. Differential sensors have two signal conductors as well as one ground signal. Both single and differential ended have a voltage conductor.

Voltage excitation is the amount of energy sent to a sensor from the VSL. Some sensors require low excitation and can be damaged with a large excitation. For example, the MP306 volumetric soil moisture content sensor requires an excitation between 6V and 15V whereas Decagon’s EC-5 volumetric soil moisture content sensor requires an excitation between 2.5V and 3V. Applying a 6V excitation to the EC-5 sensor will damage the sensor. Therefore the MP306 and EC-5 sensors are incompatible.

Power Supply:

12V DC is supplied to the VSL through a solar panel or mains. Excitation supply to sensors can be user defined between 3 and 15 Volts. The VSL has an internal lithium-polymer battery for short-term power supply during periods of no external power supply.

Sensor Outputs:

The default setting is the millivolt (mV) output from the sensor following excitation. The mV output can be converted to meaningful data via a Look-up Table, Script, or Sensor Calibration.

More Details

The VSL is a stand-alone instrument and does not need extensive cables and power requirements. All data is stored within the unit on a removable MicroSD card. Communication with the VSL is made by USB or wireless connection. Wireless is capable of up to 250m range.


The VSL has an internal lithium-polymer battery for several days field work. Batteries can be charged overnight with a CH24 power supply. In conjunction with an ICT web-based controller, the VSL and/or individual sensors can be controlled remotely. Real-time, live measurements can be made remotely from any location with internet access.

vsl with sensor

Data can be logged directly onto a remote computer or stored in the field on an ICT log server which can then be accessed via the internet. The VSL has a Windows configuration software. The software is GUI based and extremely user-friendly. Custom calibration equations or data can be entered and edited via the software. Real-time measurements, diagnostics and sensor configuration can easily be made.

The VSL has 2 wire, non-polarised bus for power input. There is no chance of incorrect wiring of positive and negative voltage because the VSL is non-polarised.

VSl multiple sensors

The VSL is IP65 rated and has been demonstrated to operate in extreme environmental conditions. Units are being used in diverse environments from hot Australian deserts, tropical Amazon rainforests, temperate German forests, Indian agricultural fields and North American Arctic cold.

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