Field Data Loggers


Sigra field data loggers may be used to collect and or transmit data. They can also be used to control local equipment or transmit warnings based on that data.

The loggers will directly read many kinds of transducer including those with voltage or frequency outputs, vibrating wire transducers or resistance devices. Digital transducers supporting Modbus can also be monitored.

Multi logger setups (supporting additional transducers) can be interconnected via an RS485 bus. These loggers can additionally be setup in a master slave configuration and take readings in turn.

Loggers are able to communicate via radio. Radio communication is supported via plug in modules. The country of operation and or range required dictate which modules are employed. Options are available for the 920MHz or 2.4GHz ISM bands. Both options offer a self healing mesh network with inter logger ranges of 1km (at 2.4GHz) to 7km (at 920MHz) using an omnidirectional antenna. Larger areas can be covered by adding more radio equipped loggers. A network using five hops could cover 35km (at 920MHz).

The loggers can be used to transmit to the outside world via any transmitter using an RS232 input. This includes, but is not limited to, high power radio transmitters or PSTN, 3G/4G or satellite data modems. Thus data can be acquired from virtually any location on the planet if one of these communications mediums are available.

The data transmitted may be acquired by the clients own data acquisition system or generally and more conveniently by Sigra who will collect and place it on the web for secure access by the client.

At Sigra, we can do more than just collect data. We can also check on the health of the field system remotely, process information, and in some locations provide installation and service for the equipment.

The loggers can also be used to control devices. They are programmable to determine whether certain conditions have been reached and to activate devices.

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The application for this technology is wide.  The field applications may include:

  • Landslide or excavation monitoring by the use of
    • Piezometers
    • Tiltmeters
    • Fixed Inclinometers
    • Extensiometers

NB. In this application the loggers may be used to activate warnings as well as provide data

  • Ground anchor monitoring
  • Stress changes during or post excavation from surface or underground
  • Aquifer and pore pressure monitoring
  • Petroleum reservoir monitoring

Any of these applications may require the controlled operation of pumps to move liquid.

Examples of Use
The monitoring of a large landslide

Sigra has installed a monitoring  system on an area subject to landslide comprising a mass of igneous rock overlying sedimentary material. The contact has very low friction and moves continuously and at an increased rate when it rains and groundwater levels rise.

The monitoring system comprises multiple loggers in a network that collects rainfall, piezometric and pump operation information. The system controls pumps in wells designed to dewater the slope and help control the landslide.

A 3G modem connected to one of the loggers in the network is used to remotely collect data from the networked loggers. This automated process is repeated several times each day. Sigra makes the data available to the client via a secure web server. To reduce the amount of data the client has to review, the loggers are configured to record only when data changes by more than a set amount. A heartbeat record at a longer interval is still recorded to reassure system integrity.

Reservoir monitoring

The Sigra loggers are frequently used to monitor pressures in coal seam gas reservoirs. In this case they generally monitor multiple transducers, cemented into a well.  At surface is a box containing loggers that are coupled via RS485 and communicate to the outside world via a modem.  The units are powered by a solar cell which stores energy in batteries.
In another variant of this Sigra can configure the system to control well pumps as well as monitor well pressures and flows.


Sigra’s Field Data Logger is a low power, versatile, eight channel device designed to monitor several types of sensors:

  • Vibrating Wire
  • Voltage
  • Frequency
  • Resistance (Thermistors)
  • Switches (Reed Switch, Rain Gauge, Flow Meter)
  • Digital Modbus RS485 Sensors

With external interfaces it may also be used to monitor:

  • Current loop
  • Strain gauges
  • Other upon request

NB. Using one of these interfaces removes the ability to use Modbus on the RS485 port.


Communication with the logger can be achieved by:

  • Direct cable to PC (USB or RS232)
  • Data modem (any modem with RS232 port)
  • Logger to Logger radio or RS485 (or both) network

The radio modules provide mesh networking which has the advantages of self-healing. These modules operate in the ISM bands. Please contact Sigra for advice when choosing radio modules.

Modbus Capability

Modbus RTU on the RS485 port and RS232 port.

Modbus ASCII on the RS232 port allows integration into SCADA systems.


Windows based software allows the setup and downloading of the data logger via any communications interface (other than interfaces setup for Modbus).

Plenty of Storage

The Sigra Data Logger V9 comes with a 4 GB micro-SD card built-in to permit lifetime storage.

Improved Resolution

By storing the records in a 32-bit floating point format, improved resolution of 0.001 Hz is available for Vibrating Wires without affecting coefficients for previously installed transducers. This allows seamless upgrade of existing Vibrating Wire installations for improved resolution.

  1. For Vibrating Wires used in surface applications (strain gauge, shallow piezos etc.), the temperature drift will be significant at these resolutions.
Stable Clocks

The internal clock chip with a built-in crystal oscillator has a time drift of less than 2 minutes a year across the full operating temperature range. Less than 20 seconds of drift is achievable if maintained between 10 and 40 degrees Celsius.

Low Voltage Disconnect

The V9 Data Logger (IP65 version) now has a built-in Low Voltage Disconnect (LVD) to protect the batteries from extreme discharge. This prevents the early failure of cells.


The loggers have an alarm capability that permits them to detect when a value exceeds a threshold value, rate or both. The logger can then send a warning via SMS message (requires a 3G modem), trigger an output and store the alarm as a flag when downloaded. Alarms are sent through the local logger network to permit warning devices across the site to be activated.

Process Control

The V9 Data Logger can control pumps and other devices in an on/off fashion with hysteresis.



  • 8 Channels for Voltage, Resistance and Frequency.
  • 4 may be used for Vibrating Wire or Process Control outputs. (Odd Channels).
  • 4 may be used for Switching Inputs. (Even channels).

Range and Resolution:

  • Vibrating Wire:
    • Range: 0.5 – 5 kHz
    • Resolution: 0.001 Hz
    • Raw unit: 0.1 Hz
  • Resistance:
    • Range: 0 – 220 kΩ
    • Resolution: 1 Ω
    • Raw unit: 1 Ω
  • Voltage:
    • Range: 0 – 5 V (Use an external potential divider for higher voltages.)
    • Resolution: 77 µV (16 bit)
    • Raw unit: 77 µV
  • Switches:
    • Cumulative counts or reset on read.
    • Rate: 0 – 100 Hz
    • Raw unit: 1 switch (on and off cycle)
  • Radio:
    • Frequency: 2.4 GHz ISM Band or 920 MHz
    • Transmit Power: 63mW and 250 mW respectively
    • Receive Sensitivity: -100 dBm
    • Supplied Antenna: RFI CSM700
    • Optional Antennas: Higher gains available on request.

Process Control:

  • On/Off with Hysteresis
  • Based on result of another channel on the same logger
  • Digital control signal
  • 5 V (external interface may be required to drive SSR’s or Relays)


  • Rechargeable battery with solar panel for weatherproof enclosure

Switched Power Out:

  • +5V for sensors 10mA current available.

Environmental Rating:

  • DIN Mounting: IP20
  • Weatherproof enclosure: IP65


  • Compatible with Windows XP, Vista, 7, 8

These options are typically set up in a fan or daisy chain of loggers on site which communicate with a base station logger connected to a modem on the mobile network. In this configuration data is available on-line.

The basic logger radio is typically capable of 200 to 800 m line of site communication. This range is dependent on site conditions.

logger wireless small


  • Firmware update
  • Logger software
  • Logger manual

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