Intended use

The operator is responsible for assessing the suitability of Quadbeam sensors for an application, for their intended and actual use, and and for resistance of the sensor components against degradation in the environment. The manufacturer is not liable for any damages resulting from the use of the sensor beyond the cost of the sensor. Quadbeam sensors are intended for use in industrial, storm water, raw water or waste water installations for continuous monitoring of suspended solids.

Product warranty

Quadbeam sensors have a warranty against defects in materials and workmanship for one year from the date of shipment. During this period, Quadbeam will, at its own discretion, either repair or replace products that prove to be defective.

Limitation of warranty

No warranty of fitness for a particular purpose is offered. The user assumes the entire risk of using the product. Warranty does not cover damage caused by accidental misuse, abuse, neglect, misapplication or modification. Any liability of Quadbeam Technologies Ltd is limited exclusively to the replacement of defective materials or workmanship.


Quadbeam Technologies Ltd reserves the right to make changes to this guide or the instrument without notice, as part of our policy of continued development and improvement. All care has been taken to ensure the accuracy of the information in this guide. However, we do not accept responsibility for any losses or damage resulting from errors or inaccuracies of the information in this guide.

Technologies commonly used in suspended solids and turbidity sensors

Quadbeam uses the four-beam alternating light ratio-metric system of measurement for its sensors, which operate on 880 nm near-infrared (NIR) light.

Suspended solids sensors and turbidity sensors measure changes in light intensity to produce a relative measure of the solids or turbidity concentration in the liquid being monitored. Most commonly sold suspended solids sensors and turbidity meters use only a single beam of light, meaning that light intensity can be influenced not only by suspended solids particles but also by any solids/contamination stuck to the surface of the sensor. This is why single-beam sensors need constant cleaning. However, their measurement of light intensity can also be influenced by variations in the light source and LED as they age.

Multi-beam sensors measure light intensity across multiple light paths. Quadbeam sensors combine these measurements in a ratio using mathematical algorithms. This ratio automatically compensates for contamination stuck to the surface of the sensor and for variation in the sensor's light components, making Quadbeam sensors more accurate and reliable than single-beam sensors. That's why multi-beam sensors are often used in process control installations where a repeatable output is very important.

Common single-beam configurations

Signal drifts as sensor ages or gets contaminated

Multi-beam configurations

Algorithm compensates for contamination and ageing giving very repeatable signals

Sensor types

S10-2HY Inline Hygienic style 3A Certified

S10-2HY Inline Hygienic style 3A Certified

Example application: measures 0-40% milk fat. 2" Triclover fitting.  

S10-3HY Inline Hygienic style 3A Certified

S10-3HY Inline Hygienic style 3A Certified

Example application: measures 0-40% milk fat. 3" Triclover fitting.

S10-IMM Immersion Style

S10-IMM Immersion Style

Example concentration: 0-25 g/L SiO2. Applications include return and waste-activated sludge measurement, clarifier monitoring.

S10HT-3HY Inline Hygienic Style

S10HT-3HY Inline Hygienic Style

Operates to 105°C. Example application: CIP optimisation, measures 0-40% milk fat. 3" Triclover fitting.

S20-3HY Inline Hygienic Style 3A Certified

S20-3HY Inline Hygienic Style 3A Certified

Example application: measures 0-20% milk fat. 3" Triclover fitting.

S20-IMM Immersion Style

S20-IMM Immersion Style

Example concentration: 0-10 g/L SiO2. Applications include Loss Monitoring, Clarifier monitoring and control.

S20-VN Varinline® Inline Hygienic Style

S20-VN Varinline® Inline Hygienic Style

Example application: measures 0-20% milk fat. To fit Type N Varinline access unit.

S20HT-3HY Inline Hygienic Style

S20HT-3HY Inline Hygienic Style

Operates to 105°C. Example application: CIP optimisation, measures 0-20% milk fat. 3" Triclover fitting.

S40-3HY Inline Hygienic Style 3A Certified

S40-3HY Inline Hygienic Style 3A Certified

Example application: measures 0-1.5% milk fat. 3" Triclover fitting.

S40-IMM Immersion Style

S40-IMM Immersion Style

Example concentration: 0-2.5 g/L SiO2. Applications include filtration monitoring, clarifier monitoring.  

S40-VN Varinline® Inline Hygienic Style

S40-VN Varinline® Inline Hygienic Style

Example application: measures 0-1.5% milk fat. To fit Type N Varinline access unit.

T30-3HY Hygienic Style 3A Certified

T30-3HY Hygienic Style 3A Certified

Example application: measures 0-50 to 0-1000 NTU. 3" Triclover fitting.

T30-IMM Immersion Style

T30-IMM Immersion Style

Measures 0-50 to 0-1000 NTU.

Jet cleaner attachment

Quadbeam sensors typically only need occasional cleaning at most because their multi-beam technology self-compensates for accumulated contamination. However, in applications where extra cleaning is required, a cleaning guard connected to a hose supplying an occasional burst of compressed air or water can be fitted.

Pipe installation

Hygienic pipe installation
Quadbeam hygienic sensors come in HY and VN configurations. All 3HY sensors fit the standard 3” tri-clamp fitting.
The S10-2HY fits a standard 2” tri-clamp fitting.
The VN sensors fit the GEA Varinline® Type N access unit.

Immersion installation

The sensors work by measuring the change in light intensity. Therefore anything that can reflect, deflect or absorb the light will affect the output of the sensor.

Keep a "Clear Zone"
To reduce the chance of light reflection off walls of flumes, tanks, channels, sumps etc, it is recommended where possible to have a “Clear Zone” from all objects of at least 50mm (2”). Ensure that the sensor is fixed in place. The thread at the back of the immersion-style sensor is 1 1/4" NPT and will fit many standard 32mm plastic fittings.

Things that can change the reflected or absorbed light, and therefore affect the output of the sensor include:

  • Suspended solids
  • Some background chemicals (e.g. copper)
  • Air bubbles
  • Low level balance tanks
  • Centrifugal pumps
  • Bends, valves and other instruments that could engender entrained air
  • Aeration sparge pipes
  • Liquid inflows into sumps and drains
  • Pressure drop
  • Light
  • Pipe walls
  • Different materials that react differently to 880 nm NIR light, e.g. protein and fat
  • Temperature on material NIR absorption
  • Particle size, colour and shape

Pipe installation

  • The minimum pipe diameter for S10-2HY is 50mm (2”). For S10-3HY, S20-3HY and S40-3HY and T30-3HY, the minimum is 75mm (3”). For best results for S40-3HY and T30-3HY, we recommend a minimum of 100mm (4”).
  • The sensor should be mounted in a straight pipe where there are 10 pipe diameters upstream and 5 pipe diameters downstream that are free from valves and bends.
  • It is preferable that the sensor is installed at a vertical pipe where the flow is upwards (1). This ensures that the pipe is always full. A downwards flow is not recommended as the fluid could have some turbulence which could result in an unstable reading (5).
    If there is a bend within 10 pipe diameters place the sensor on the side of the pipe closest to the inside of the bend.
  • If only a horizontal pipe is available the sensor should be installed in the horizontal plane ± 45° (2). Avoid placing the sensor at the top of the pipe as the pipe may not always be full or there could be an accumulation of bubbles (3). Usually the bottom of the pipe should be avoided as it could have a higher than normal concentration of solids (4) (though see below for installations with a very high chance of entrained air).
  • For sensor installation drawings, as below, please contact your Quadbeam distributor.
  • In installations where there is a very high chance of entrained air, for example CIP monitoring and control applications, the best position is in fact at the bottom of a horizontal pipe. For added protection against the chance of entrained air, expand the pipe eccentrically keeping the top of the pipe inline and the eccentric expansion at the lower section of the pipe. Increasing the pipe diameter effectively slows the flow encouraging the bubbles to the top of the pipe.
  • COW water solids monitoring applications are tricky as the concentration of solids is very low and entrained air can be present. If the pipe is vertical, increasing the diameter can help reduce the potential for entrained air being detected. If there is only a horizontal option, eccentric expansion has proven to give good results with the feed being lower than the outflow and the sensor positioned away from the feed.
  • In applications where solids have a propensity to stick, the sensor can be mounted at an 80° angle to the pipe so the flow of the solution assists in sensor cleaning (see diagram below). A sample line should be added after the sensor as shown. It should not be at the same point as the sensor or immediately before it.
  • For immersion sensors, the pipe neck is terminated with a flange. A mating flange with a 1 1⁄4 inch hole should be used to hold the sensor. This installation should not be used in hygienic applications.

Drain installation

There are three main issues to consider for drain installations:
1. make sure that the drain is always full so that the end of the sensor - the "fingers" - is always immersed in the solution. Failure to do so could result in unpredictable readings;
2. keep ambient light constant in order to avoid variations in reading between day and night. If the drain or flume is open to the atmosphere, protection from sunlight will reduce the chance of abnormal readings produced by scattered or direct sunlight;
3. place the sensor in a position with the lowest possibility of foam or bubbles (e.g. caused by turbulence), as they can affect readings.

Vertical mount

The vertical mount is most common as it can be implemented in shallow channels. A horizontal mount is used in covered drains where it is not possible to implement a vertical mount (described in the next section). An immersion-style sensor should be used for drain installations.

In this vertical mount, a pipe is attached to the 1 3⁄4 inch thread at the back of the sensor. This pipe is then fixed to the drain by pipe clamps. For T30 sensors, which have a bigger body than the S-series sensors, the pipe clamps could be mounted directly on to the sensor. Care must be taken to avoid over-tightening the clamps and possibly damaging the sensor.

For S-series sensors, if the flow in the channel is not deep enough, a longitudinal hole can be created to ensure that the sensor fingers are continuously immersed, with the recommended Clear Zone.

Horizontal mount

A vertical mount is not possible in some cases, for example in covered drains. In these situations the sensor can be mounted horizontally along the flow. It should be mounted using the 1 1⁄4 inch thread with a short pipe that connects to an elbow typically having a 90° angle. The other end of the elbow connects to a longer pipe which is mounted with pipe clamps.

Dimensions (A) and (B) should be 50mm (2”) for S-series sensors, and 75mm (3”) for T-series sensors to provide a “Clear Zone”. Dimension (C) should be at least 50mm (4”) for both series.

In this set-up, the minimum channel depth is 150mm (6”) for S-series sensors and 175mm (7”) for T-series sensors.

The sensor should be installed such that the two IR transmitters (black-looking ) are at the bottom facing upwards and the two IR receivers are at the top facing downwards. This minimizes interference from ambient light changes. The front of the sensor should be facing downstream.

Tank installation

This installation is set up with an immersion-style sensor. The thread at the back of the sensor is used to mount it at the end of a pipe. This pipe is fixed to the side of the tank wall using clamps as shown. Ensure the clamps push the sensor far enough away from the wall to maintain the Clear Zone. It is recommended that the sensor is installed approximately half-way down the tank. If the tank is shallow, it is preferable that the sensor is closer to the bottom rather than the top, to avoid the effect of ambient light changes.

It is also recommended to install an elbow in the pipe as shown, to push the sensor away from the wall and closer to the centre of the tank.

If the tank or sump is open to the atmosphere, protection from sunlight will reduce the chance of abnormal readings produced by scattered or direct sunlight.

Manifold installation

In loss monitoring installations in dairy plants where there are multiple points of measure, for example conductivity, pH and temperature as well as suspended solids or turbidity, it can be advantageous to run the monitored fluid through an instrument manifold.


Quadbeam sensors have a very repeatable output because they use the four-beam, ratio-metric principle. Therefore, the more care that is taken in setting up the sensors, the more accurate the output will be. The output is only as good as the quality of the calibration and installation.

MXD70 manuals
Comprehensive instructions for the MXD73 and MXD75 transmitters are available in manuals at

Relative measurement - Probe Signal (PS)
In the linearisation process, the probe signal (PS) value is related to concentrations of suspended solids in the solution being used for calibration. The PS is a binary number generated by the input card that has an “engineering” value applied to it in the transmitter “lineariser”. The PS is the result of the four-beam ratio-metric output, meaning it is the repeatable part of the process. The sensors are analogue or have an analogue component which means each sensor/input card combination will be a little different.

  • The calibration process ties the PS value to an “engineering” value.
  • The engineering value can be measured in multiple ways, for example, %, mg/l, g/l, ppm, ppt, NTU, FTU and PS.
  • Once the relationship between the PS and the engineering value is established, the front screen information, analogue output, relay alarms and fine tuning can be set up.

Calibration standards
The sensors measure the intensity of NIR light emitted across the sensor light paths. Different materials absorb or scatter NIR light in different ways. For best results, where possible, use the actual process fluid and solids being measured as standards to set up the linearisation of the sensors.

It is not uncommon for pre-prepared solutions to be used, for example NTU solutions or varying concentrations of SiO2 in water. These work very well as repeatable standards, but installers should ask whether they are directly relevant to what is being measured and are understood by operators?

It is possible to have up to 10 points in a calibration curve. Some materials have a linear response to 880 nm NIR, for example NTU solutions and SiO2. Some materials have a non-linear response, for example milk fat. In non-linear applications like milk fat monitoring we recommend calibrating at least 5 points on the curve. Where relatively tight control is required we recommend clustering the calibration points around the control range.

Simple calibration
After preparing your samples, work through the following menu steps:

For comprehensive set-up details, see the Quadbeam MXD70 Suspended Solids Input manual.

When ready for actual curve set-up, place the sensor in opaque cups ensuring the bottom of the sensor fingers are at least 20mm from the bottom of the cup and the sensor is centralised. Complete the following steps:

Repeat for each point on the calibration curve.

Because of the variance between inline measurement and calibration cups, it is possible to do a fine adjustment after the sensor has been installed.

1. Once installed, take a grab sample at the same time as reading the sensor output.

2. Analyse the sample in the lab.

3. If required to bring into line with the lab reading, move the zero point of offset by working through the calibration menu accessed from the main menu.

Better calibration
To help eliminate variability in the set-up, build a set of calibration vessels as close as practical to the actual pipe work.

Work through the same steps as above.

Best calibration (for tight control applications)
For applications involving tight control, for example fat standardising or yogurt concentration control, install the sensor with a sample port as soon after the sensor as practical.

For comprehensive set-up details, see the Quadbeam MXD70 Suspended Solids Input manual.

Take a sample during operation, and at the same time note down the PS value showing on the MXD transmitter.

Vary the operation to change the solids concentration, take another sample and record the PS value again.

Repeat at least five times with varying solids concentrations.

Have the lab analyse the samples and provide the solids concentration. It is often useful to have the lab run “same sample” tests to ensure lab-repeatable testing.

When the solids concentration is established from the lab, go back to the MXD transmitter and manually input the concentration values against the PS values recorded at the time of sample extraction.

Please note that higher concentration samples should have a higher PS value than lower concentration samples.

Input filter
It can help to add an input filter for installations where the data is changing rapidly.

The life of the sensor can be extended by activating CIP mode to turn off the sensor head if it is not being used for measuring the hot processes during CIP.

Appendix A

Setting up multiple curves that can be switched remotely

Operation overview
After setting up the three curves, saving two of them to separate stores and assigning two digital inputs to those stores, you will be able to switch between them.
With no digital inputs you will be in a neutral position so the active curve will operate.
Activate Digital input assigned to store A will switch set-up to store A.
Activate Digital input assigned to store B will switch setup to store B.
You always have to go back to neutral before switching from A to B.

Setting up curves

Curve set-up A
Set-up the channel, curve and outputs in the normal way.

From the main menu go to: SAVE/RESTORE


Curve set up B
Repeat the process for channel, curve and cutput set-up B, but this time save in SAVE B.

Curve set-up neutral
For your third curve, set-up the curve and output in the normal way. Do not save. For security you can back-up the whole unit to an SD card.

Setting up digital inputs

For curve A

From the main menu go to digital inputs:

Select the input:

Select the channel
Set function to Switch Channel
Set Store to Store A

For curve B
Repeat the process for Digital Input 2 and Store B.

For curve neutral
No digital input activated. Set up the curve in the normal way, do not save.

Connect digital inputs.

To select curve A, activate Digital Input 1.
To select curve B, activate Digital Input 2.
To select curve neutral - do not activate Digital Input 1 or 2.