NX260 Turbidity Sensor User Guide

The NexSens NX260 Turbidity Sensor is an optical, self-cleaning sensor designed to measure turbidity. It is ideal for construction sites, dredging projects, stormwater monitoring, and other water quality applications where suspended sediments and water clarity are a concern.

1. Install software and set up the computer

1. Download and install NexSens CONNECT software on a field or lab computer.
2. Plug the MCIL-6-FS to USB cable adapter into the computer.
3. Ensure the computer has access to the internet so the USB VCP drivers install automatically.
4. Open Windows Device Manager and note the COM port for the USB Serial Port.
5. If the device does not install properly, contact your IT administrator to manually install drivers from the VCP Driver download.

2. Power the sensor and prepare for measurements

1. Connect the sensor to the cable.
2. Plug the DC power adapter into a wall outlet. The wiper will activate on power up (three back and forth cycles).
3. Half fill a 1-liter amber-colored bottle with clean tap water.
4. Suspend the sensor in the center, a minimum of 4 inches (10 cm) from the bottom. This will reduce reflected and ambient light interference.

 

3. Confirm sensor connection and function

1. Open CONNECT software and go to Tool → Sensor → NexSens NX260 Turbidity
2. Select and Apply the previously noted COM port, and sensor readings will begin updating.
3. Click the gear icon to activate the wiper.
4. When the wiper finishes the cleaning cycle, note the tap water reading.
5. If available, transfer the sensor to other samples with varying turbidity and watch the sensor readings. Always activate the wiper when entering a new sample to ensure the face is clean and free of bubbles.
6. Rinse and dry the sensor before returning to the amber bottle to confirm the initial reading.

 

4. Calibrate the sensor

The NX260 supports one and two-point calibration. For most surface water applications, a two-point in 0 FNU and 100-200 FNU is recommended. The most recent calibration coefficients are stored within the sensor. Calibrations are performed one point at a time, and coefficients are updated individually. Follow Good Laboratory Practices (GLP) to ensure accurate readings. For best results, a stabilized Formazin standard, such as Hach Stablcal is recommended

1. One-Point Turbidity Calibration
   1. Open the 1-Point Turbidity Calibration in the software
   2. Pour 500 mL of calibration reagent into an amber bottle.
   3. Suspend the sensor in the center and a minimum of 4 inches from the bottom.
   4. Enter the reagent value and activate the wiper.
   5. Click Start Calibration and allow 30 to 60 seconds for readings to stabilize.
   6. Once stable, select Accept.
   7. Rinse and dry the sensor.
2. Two-Point Turbidity Calibration
   1. Go to Tool → Sensor → NexSens NX260 Turbidity in CONNECT software and open 2-Point Turbidity Calibration.
   2. Pour ½-liter into an amber bottle with the lower value reagent.
   3. Suspend the sensor in the center and a minimum of 4 inches from the bottom.
   4. Enter both reagent values (e.g., 0 and 100 FNU) and activate the wiper.
   5. Click Start Calibration and wait 30–60 seconds for readings to stabilize.
   6. Click Accept to store the first point.
   7. Rinse and dry the sensor.
   8. Place the sensor in the second reagent, wipe and allow 30–60 seconds for readings to stabilize.
   9. Click Accept to store the second point.

 

5. Post-Calibration Checks

1. Return the sensor to calibration reagents and check that the sensor readings are within an acceptable tolerance.

 

6. Data Logger Connection

The NX260 interfaces to data loggers with RS-485 Modbus protocol or SDI-12 with an optional adapter.

Connecting to NexSens X-Series Data Loggers

1. Use CONNECT Software to set the Modbus address.
   1. Go to Tool → Sensor → NexSens NX260 Turbidity in CONNECT software and select the Gear icon.
   2. At the top, enter the new Modbus address and select Update Sensor.
      
2. Connect the sensor using the supplied cable to one of the open sensor ports on the logger and note the port number.
3. Plug the X3 into the USB port of the computer and power it on with the AC power cable.
4. Open CONNECT and select the SENSOR tab.
   
5. Click Add and select NexSens from the Manufacturer drop-down. Then select the NX260.
6. Set the port number.
7. Select either Continuous or Switch in the Power drop-down.
   1. Switch power is recommended for the NX260 turbidity sensor.
      
8. Click Save Sensor Profile.
9. Complete the setup for all other sensors, and then click Deploy.
   
10. Confirm that data is being transferred to WQData LIVE.

Connecting to SDI-12 Data Loggers

Use the optional RS485-SDI12 adaptor to convert the sensor to SDI-12. Connect as shown and follow standard SDI-12 protocol.

Signal	Color
12V	Red
Ground	Black
SDI	Brown
A	N/C
B	N/C

 

Connecting to Other RS-485 Modbus Data Loggers

For other RS-485 Modbus data loggers, use the wiring pinout and Modbus commands found in Appendix A.

 

7. Mounting

Deployment setups will vary based on the platform, application, and site location. For general buoy mounting instructions and pole-mount assembly, see below.

Buoy-Based Deployments

First, follow the appropriate User Guide in the Knowledge Base for buoy assembly. There are two options for near-surface measurements and a third option for water column measurements:

Cage Mount

Use the NexSens Small Instrument Cage Mount to attach the sensor to the buoy cage. 

1. Strap the sensor to the gage leg with the mount and cable ties (as shown). The mount is supplied with a rubber adhesive liner to prevent the sensor from sliding.
   
2. Further secure the assembly by adding a few additional ties to the cable.

Buoy Deployment Pipe

Optional perforated deployment pipes can be fitted to most NexSens CB– and XB-series buoys. Deploying the sensor inside the pipe provides easy access for maintenance and recalibration.

 

Water Column

Use the NexSens Instrument Mooring Clamp to securely attach NX260 to a sensor mooring line at the desired depth in the water column.

 

Shore-based Deployments

For dock, pier, or bank deployments, it’s best to secure the sensor in a perforated PVC pipe. Extend the pipe into the water and deploy the sensor.

 

 

8. Inspection and Maintenance

Periodic inspection and maintenance ensure that the NX260 provides reliable and accurate field measurements for long-term continuous operation. Follow a quality assurance plan (QAP) and agency requirements.

1. Visit the monitoring site and perform a calibration check by leaving the sensor in place and making a nearby independent turbidity measurement with a field sampling instrument. The readings may be used as a QC data point to help understand sensor drift or used to determine calibration frequency.
2. Pull the sensor from the water, and if fouled, clean it with tap water and a soft cloth. In extreme fouling environments, a brush and detergent may be needed. Be careful not to scratch the optical window, and do not turn the wiper by hand as this could damage the motor or gearbox.
3. Calibrate the sensor if needed or required by the QAP.
4. Check that the connection remains tight and return the sensor to the water.
5. Before leaving the site, confirm data is again streaming to the cloud or base station.

 

Cleaning

Periodic cleaning will extend the life of the sensor and help ensure long-term quality data. Soak the sensor in a mild dish detergent for 10 to 15 minutes. Being careful not to scratch the optical sensing elements, lightly brush or wipe away any debris. If hardness and other deposits persist, soak the probe in a 50% by volume vinegar and water solution and brush or wipe as needed. Rinse and dry the sensor.

 

Wiper Replacement

Anytime the sensor is calibrated or cleaned, Users should check the wiper to ensure that there are no frays on the brush and that there are no black streaks on the sensor face. If either of these is noticed, the wiper should be replaced.

All NX260 sensors come with one Replacement Wiper Kit. Additional kits can be ordered online under part number: 260-wiper.

1. Clean off the sensor and unplug it from the power source to stop the wiper from running during the replacement.
2. Using the included Allen wrench, loosen the top screw. 
3. Once loosened, remove the old wiper.
4. Insert the new wiper, divot facing up toward the set screw on the bracket, then tighten it in place.

 

9. Troubleshooting

Troubleshooting NX260 problems is best done by first connecting the sensor to NexSens CONNECT software.

Error or Problem	Potential Causes	Solutions
Wiper parked over optics	Sensor powered off during cleaning cycle. Sensor failure	Unplug and reconnect the power. The sensor wiper will reset. Contact NexSens support
Internal damage	—	Contact NexSens support for return instructions.
Negative turbidity readings	Sample clearer than 0 FNU calibration reagent Sensor optical signal receiving stray or ambient light during calibration	Be sure to use a clean 0 FNU cal reagent. Center the sensor in an amber bottle, a minimum of 4 inches from the bottom, during calibration
Sensor readings not updating	Communication failure	Check cable connections and power. Check if the wiper is turning. Check the Com port
Erratic readings	Air bubbles or debris on sensor face Sensor failure	Visually inspect the sensor face. When returned to water, initiate a wipe cycle. Contact NexSens support
Calibration error	Erroneous calibration constants	Uncal and recalibrate

 

10. NexSens Warranty

View the NexSens Warranty.

 

11. NexSens Service Request

To return equipment for evaluation and repair, visit this page for more information.

 

Appendix A

RS-485 Modbus wiring pinout and commands.

Register Address (Hex)	# of Registers	Name	Access	Limits or Range	Units	Data	Function Code	Comments	Test Request	Test Response
12288 (0x3000)	1	Get/Set Modbus Device address	Read/Write	1-247	—	16-bit integer little endian	03, 16	Use Get command with universal address 255 (0xFF)	FF,03,30,00,00,01,9E,D4 (Get Slave ID)	FF,03,02,03,00,91,60 (Slave ID)
1792 (0x0700)	2	Get Software and Hardware Revision	Read Only	—	—	16-bit unsigned	03	Register 1 = Hardware Register 2 = Software	01,03,07,00,00,02,C5,7F	01,03,04,01,07,03,01,8B,3E (HW: 1.07, SW: 3.01)
2304 (0x0900)	7	Get SN	Read Only	—	—	ASCII	03	Byte 0: Reserved Byte 1–13: 12 character null terminated ASCII string serial number	01,03,09,00,00,07,07,94	01,03,0E,29,59,4C,32,39,32,34,30,31,30,38,30,31,00,0C,7D (YL2924010801)
9472 (0x2500)	1	Start Measurement	Read Only	—	—	16-bit integer little endian	03	By default, measurements will output every second.	01,03,25,00,00,01,8F,06	01,03,02,00,00,B8,44
11776 (0x2E00)	1	Stop Measurement	Read Only	—	—	16-bit integer little endian	03	—	01,03,2E,00,00,01,8D,22	01,03,02,00,00,B8,44
9728 (0x2600)	5	Get Temperature and Turbidity Values	Read Only		Temperature: °C Turbidity: FTU	Floating point (Little endian)	03	Register 1–2: Temperature Register 3–4: Turbidity Register 5: Error flag	01,03,26,00,00,05,8E,81	01,03,0A,A0,5F,B9,41,78,7B,9C,41,00,00,95,EB Temperature = 23.17°C (0x41B95FA0) Turbidity = 19.560287 (0x419C7B78) Error Flag = 0 (0x0000)
4352 (0x1100)	4	Get/Set User Calibration Coefficients	Read/Write	—	—	Floating point (Little endian)	03, 16	Register 1–2: K Value Register 3–4: B Value	01,03,11,00,00,04,41,35 (Get calibration coefficients)	01,03,08,00,00,80,3F,00,00,00,00,9E,12 K-value: 1.00 (0x3F800000) B-value: 0.00 (0x00000000)
6912 (0x1B00)	1	Brush power-on startup settings	Write Only	—	—	16-bit integer little endian	16	0x0000: Does not start on power 0x0100: Power on and self-start
12544 (0x3100)	0	Activate Wiper	Write Only	—	—	16-bit integer little endian	16	The wiper will make four rotations in each direction.	01,10,31,00,00,00,00,74,94	01,10,31,00,00,00,CE,F5
12800 (0x3200)	1	Get/Set Wiper Interval	Read/Write	—	—	16-bit integer little endian	03, 16		01,03,32,00,00,01,8A,B2 (Get wiper interval)	01,03,02,1E,00,B1,E4