Suspended Solids Monitor – SoliSense®

Optical measurements for Total Suspended Solids monitoring have been available for many years and are used in many water, waste water, and industrial settings. However, did you know that…
…the use of multiple path lengths can extend the range of optical sensors?
…the use of longer wavelength emitters can reduce the effect of colour on the readings?
…the use of multiple emitter intensities can mean that no zero is required and can eliminate the effect of background light (patented by Pi)?

Total Suspended Solids Monitoring (TSS)

TSS monitoring is essential for controlling many industrial processes, especially in Waste Water Treatment plants when an understanding of the solids load and solids movement around the plant is essential to efficient plant outcomes.

The standard method of gravimetric sampling (passing a known volume of TSS containing water through a filter, then drying the filter and measuring the weight gain to give a measure of mass/volume – TSS) is slow and cumbersome and subject to errors, e.g. sampling errors. What is needed is a device that can measure the TSS continuously and online.

The most common devices are based on the measurement of the optical properties of the sample, commonly backscatter.

Multiple path lengths for the greatest range

There are some fundamental problems with using backscatter to measure TSS. The first is the range that a sensor can measure over. This is largely determined by the path length of the sensor. The longer the path length, the greater the sensitivity but the smaller the range.

This is because as solids increase, the backscatter (signal) increases but so does the attenuation (blocking) of the light until their effect is equal (the ‘hump’) after which attenuation increases until the signal is zero.

This means that a meaningful measure of TSS can be made going up the slope (measurement zone A) and going down the slope (measurement zone B). The problem with this is that the different samples will have a ‘hump’ where measurements aren’t possible in different places.

For most manufacturers, the solution is to quite tightly define the range at which the sensor can operate. Pi’s SoliSense^®s uses two detectors of different path lengths to measure the widest possible range of TSS in a single sensor.

Using long wavelength emitters decreases the effect of colour

Devices that use shorter wavelengths (blue, green, white) are more affected by the absorption of those wavelengths by the solids in the sample. Effectively some of the signal is lost to absorption rather than being available to scatter. The SoliSense^® uses an emitter at 860nm to minimise the absorption of the emitted light left to sample.

Using multiple emitter intensities allows for no zero, and the elimination of the effects of ambient light

Each time the SoliSense^® takes a measurement it isn’t simply measuring the amount of backscattered light (which includes an element of ambient light). It changes the amount of light emitted to 25%, 50%, 75% and 100%. From there it records a gradient for each sample point. As it does this very quickly it can be assumed that the ambient light is constant and is therefore absent from the gradient (compensated out). In addition, doing this during a calibration allows the SoliSense^® to back calibrate any zero offsets and remove these. This capability is patented by Pi and is unique in the marketplace.

Conclusion

The SoliSense^® from Pi uses patented technology to

• give the widest range of any currently available optically based TSS sensor
• minimises the effect of colour on the measurement of TSS
• compensates for zero drift and ambient light.

All of which means that the SoliSense^® is an extremely effective technology for continuously measuring Total Suspended Solids in industrial and municipal waste water treatment plants.

Many different sites ranging across the whole water industry have a daily struggle to keep instrumentation functioning correctly due to fouling. However, did you know that…
…self cleaning and self flushing systems are now available from Process Instruments for most types of sensors?
…these fouling removal systems can extend the life of sensors and drastically reduce maintenance regimes?
…Pi’s self cleaning/flushing systems are affordable, simple and trouble free by design?

Sensor Fouling

Whatever the process being monitored is, there is often something in the sample water capable of fouling a sensor, and therefore causing erroneous results. The obvious solution to this problem is to clean the sensor, but how regular should inspection and cleaning programs be for each piece of instrumentation? Too regular and the inspection and cleaning regime is time consuming and unnecessarily costly. Not often enough and the instrumentation will give false results and probably fail prematurely.

What is the solution?

Process Instruments’ Autoclean and Autoflush Systems

Simple, reliable and easy to maintain, Process Instruments’ Autoclean/Autoflush systems are an alternative to mechanical cleaning mechanisms which can clog and break. By regularly spraying the sensor/probe with clean water or air, the sensor remains clean and free from fouling for extended periods of time. The sensor cleaning cycle is activated by Pi’s controller for a user selectable length of time and frequency so that no matter how dirty the application, the probe remains clean. With no moving parts in the sensor body or in the cleaning attachment there is nothing to replace or check other than a simple valve positioned in an easy to reach location.

Pi’s Autoclean and Autoflush systems can give trouble free and fouling free functioning of sensors for weeks, if not months, at a time.

A solution for each application

Autoclean

This option can be added to our pH, ORP, Turbidity, Suspended Solids and Dissolved Oxygen (DO) sensors. Consisting of an end cap to direct the flow of clean water (or air for a DO sensor) across the face of the sensor blasting any dirt away. The cleaning is controlled by a single valve positioned in an easily accessible location.

Autoverify

If using air to clean a DO sensor the system can also automatically verify that the sensor is still responding correctly, removing any need to remove the sensor from the sample for months at a time.

Autoflush

For sensors that require flow cell mounting like Chlorine, Ozone and Chlorine Dioxide, an Autoflush system has inbuilt valves which automatically start/stop the sample flow and control the flow of clean water past the probe. The user can set the flushing interval and duration to keep the flow cell and sensor clear from fouling. For particularly dirty or stubborn contaminants, warm water can be used as the flush water to aid cleaning. With the above options, whatever the application or parameter being measured, Process Instruments will be able to provide a monitoring system that will not only be accurate, precise and long lasting but that will also remain free from fouling and save the operator both time and money.