Automatic Sensor Cleaning System

Process Instruments were approached in 2008 by a customer who was having to change their pH sensor every week at massive cost due to the fouling of the sensor. In response Pi developed the AutoFlush.

The idea for the AutoFlush is simple and effective. After a user defined time period, the sample drains away and the sensor and sensor housing is flushed with clean water. This water flushes the whole of the inside of the sensor housing taking away any build-up of solids to the drain. The repeated flushing of the housing and sensor helps prevent the build-up of solids and so prolongs the life of the sensor and reduces maintenance. For waxy or fatty build-ups warm water can be used to flush the sensors. As standard heavy duty pinch valves ensure reduced maintenance over a long life.

The AutoFlush can be used with Pi’s pH, ORP, free chlorine, total chlorine, ozone and chlorine dioxide sensors (or a combination of sensors) and consists of a large flow cell that automatically empties on a user selectable time basis. The signal from the sensor is held and the whole flow cell including the sensor(s) is flushed with clean water. For the original customer this meant a new pH sensor after 18 months rather than sooner, resulting in a significant improvement in process control and a very significant saving in pH sensors. Since then many customers have taken advantage of the AutoFlush and it is installed around the world in paper mills, food factories and other plants where keeping the sensors clean enhances their performance.

Probe FoulingTechnical Note459kB


It doesn’t matter what the process or application is, there is often something in the water that can cause a build-up of material, or fouling, on a sensor. This can cause erroneous results. The solution to this is to clean the sensor.

Using a Pi AutoFlush can reduce maintenance intervals, therefore extending sensor life and reducing cost. Connecting an AutoFlush to a Pi CRIUS®4.0 or CRONOS® controller enables users to select their own automatic cleaning intervals, meaning manual sensor cleaning is a thing of the past.
No. The Pi CRIUS®4.0 and CRONOS® controllers can be used to create custom settings for the AutoFlush specific to the application, including the time taken for the cleaning cycle to become active and the duration of the clean.

The AutoFlush allows users to place membraned sensors into applications normally deemed impossible, eg. meat processing plants, vegetable washing, paper and pulp.

The AutoFlush is suitable for several of Pi’s sensors including chlorine, chlorine dioxide, ozone, pH, ORP, hydrogen peroxide and peracetic acid. Two of these sensors can be installed in the AutoFlush cell at the same time.

Other Pi sensors, such as OxySense, TurbSense®, SoliSense® and UV254, do have cleaning systems available as an option.

Contact Pi to discuss.

The AutoFlush cell is maintenance free and the cell self-cleans when the cleaning cycle is activated. The sensors will still require maintenance.

The sample inside the AutoFlush cell is first drained away. The sensor housing (and therefore the sensor) is flushed with clean water. The whole of the interior sensor housing is flushed so that any build-up of solids is washed away. This is repeated at user-defined intervals to prevent solids from building up more frequently, prolonging the sensor life and reducing maintenance. For waxy or fatty build-ups, warm water can be used.

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