User Guide

The NexSens T-Node FR water temperature sensor utilizes an integral titanium thermistor secured in a protective housing for underwater deployments in fresh, brackish, or seawater. The sensors can be connected in series using UW underwater cables and suspended vertically in a water column or horizontally along a stream or riverbed. Double O-rings (both gland and face seals) ensure a reliable and watertight connection. Temperature data is transmitted on the RS-485 Modbus RTU string bus. Additionally, the T-Node FR offers pass-through signals for SDI-12 and RS-232, allowing the user to connect other environmental measurement sensors along the string. This sensorBUS architecture has been designed so researchers can easily build and customize multi-point sensor strings and environmental monitoring networks. The T-Node FR sensors feature a plug-and-play interface to NexSens X2 data loggers. For connection to external data collection platforms, the T-Node FR sensor string can integrate directly with a 3rd party data collection platform via RS-485 Modbus RTU.

NexSens T-node FR Thermistor.



  • Sensor: Thermistor
  • Range: 0 to 45 C (32 to 113 F)
  • Accuracy: +/-0.075 C
  • Resolution: 0.01 C
  • T90 Response Time: 60 seconds
  • Refresh Rate: 2 seconds
  • Maximum Sensors: 250
  • Maximum Length: 1219m (4000 ft.)
  • Communications: RS-485 Modbus RTU
  • Power Requirement: 4-28 VDC
  • Current Draw Per Node: 1.3mA active; 0.35mA sleep; 0.05mA deep sleep
  • Connector: 8 pin, sensorBUS
  • Dimensions: 7.62cm L x 3.56cm Dia. (3.0″ L x 1.4″ Dia.

Sensor Information

  • Power Requirement: 5-24VDC
  • Protocol: Modbus-RTU
  • Baud Rate: 19200
  • Parity: N81
  • Default Address: 1*
  • Universal Address: 251
  • Format: Big Endian
  • Timeout: 500ms

*On a string with multiple nodes, the nodes will be addressed in increasing numerical order. Use extreme caution when changing the address of a node in a T-Node FR string to ensure that the nodes remain in numerical order and the same address is not assigned to more than one node simultaneously.


UW-FLxR Cable Connection

The NexSens UW-Receptacle to Flying Lead cable is an accessory that may be purchased separately for integration of a T-Node FR string with a third-party data logger or SCADA system. NexSens X2-series data loggers have built-in UW-receptacle ports to accommodate a direct connection of the string.

Receptacle PinWire ColorT-Node FR Signal


NexSens UW-FLxR pinout.


Change the Modbus Address in iChart

A single T-Node FR sensor or T-Node FR/TS210 temperature string can be directly connected to a PC using a NexSens RS-485 UW Sensor USB Adapter. This adapter provides the ability to check sensor functionality or adjust the sensor’s Modbus address. Follow the article below for further information.

Change the Modbus Address of a T-Node FR


Modbus-RTU Register Information

Read Input Registers

Function 0x04 (Read input registers)
RegistersData TypeData SizePurpose
0x0006, 0x000732-bit Float, Big-endian2 registersRequests the temperature recorded by a T-node FR sensor in Celsius



Field NameHexField NameHex
Slave Address0x01Slave Address0x01
Start Address Hi0x00Byte count0x04
Start Address Lo0x06Register Value Hi0x41
Quantity of register0x00Register Value Lo0xAF
Quantity of register0x02Register Value Hi0x38
CRC Lo0x91Register Value Lo0x1D
CRC Hi0x50
  • The user has requested a temperature reading from the T-Node FR sensor with address 1. The sensor responded with 0x41af381d (21.9024°C).



Write Multiple Registers

Function 0x10 (Write Multiple registers)
RegistersData TypeData SizePurpose
0x100016-bit Integer1 registerChanges the Modbus Address of the first node on a T-Node FR string*

*Assuming the first node of the T-Node FR string begins with address 1.



Field NameHexField NameHex
Slave Address0x01Slave Address0x01
Start Address Hi0x10Start Address Hi0x10
Start Address Lo0x00Start Address Lo0x00
Quantity of register0x00Quantity of Outputs Hi0x00
Quantity of register0x01Quantity of Outputs Hi0x01
Byte count0x02CRC Lo0x05
Outputs Value Hi0x00CRC Hi0x09
Outputs Value Lo0x05
CRC Lo0x77
CRC Hi0x92
  • Using the known address of 1, the user has changed the Modbus address of the sensor with address 1 to 5.



Universal Address

The T-Node FR is programmed such that any sensor will respond to Modbus address 251. This is implemented for the event that the sensor’s current address is unknown. This address should only be queried with one sensor connected to the data line. If more than one sensor is connected, both will respond and a bad message is likely.

Note: Universal address should not be used with T-Node FR strings that have more than one node. Only use address 251 if there is a single sensor connected.


Read Current Address Using Universal Address

Function 0x04 (Read input registers)
RegistersData TypeData SizePurpose
0x100016-bit integer1 registerUses the univeral address (251) to read the current T-Node address



Field NameHexField NameHex
Slave Address0xFBSlave Address0xFB
Start Address Hi0x10Byte count0x02
Start Address Lo0x00Register Value Hi0x00
Quantity of register0x00Register Value Lo0x07
Quantity of register0x01CRC Lo0x20
CRC Lo0x21CRC Hi0xE6
CRC Hi0x50
  • Using the universal address of 251 (0xFB), the user has read that the current Modbus address of the sensor is 7 (0x0007).


Pre-Deployment Check/Setup

It is recommended that field deployments be carefully planned, and it is best to completely configure the system on a lab bench and test it for a period of time prior to taking it to the field. This will ensure a successful deployment and quality data collection. Additionally, it is much easier to troubleshoot problems in the lab than in the field.


Connector Inspection

Whenever a string is assembled or re-connected, verify that the plug and receptacle O-rings of each sensor and UW-connector cable are present and in good condition. Additionally, verify that there are no signs of moisture or corrosion on any of the T-Node FR or UW-cable connectors (if re-deploying an old string).

Inspect the plug and receptacle O-rings on each T-Node FR thermistor as well as on all sensor cables comprising the string.


TS-Clamp mooring line connection

Temperature strings are frequently attached to a mooring line to keep them fixed in place vertically within a water column. This technique helps to ensure that temperature data is consistently
being monitored at the desired depths. With the temperature string laid out on a flat surface, secure each T-Node FR to the sensor mooring line using TS-Clamp sensor mooring clamps. The TS-Clamp accessory can be used to affix a T-Node FR thermistor string to a mooring line for deployment.


Cable Armoring

For any T-node FR deployment, apply cable armor to all portions of the sensor string that have the potential to wear against irregular surfaces.



There is very little maintenance required for T-Node FR temperature strings because they are designed for long-term deployments in submersible applications.

  • Cleaning
    • Any bio-fouling that accumulates on T-node FR temperature strings during deployments should be cleaned using a soft cloth or soft-bristled brush along with soap and water.
  • Calibration
    • T-Node FR thermistors are capable of holding their factory calibration indefinitely and do not require re-calibration.
  • Storage
    • T-Node FR thermistor strings should be stored in a cool, dry place.