Hot Media, Full Line Pressure, Zero Operator Exposure: How the SensoGate WA 130 Retracts a Sensor Safely
Taking a sensor out of a pressurised line sounds like shutdown work. In most plants it is exactly that: isolate the section, bleed the pressure, wait for the medium to cool, then change the probe. The process stops or, more often, waits while the sensor drifts uncalibrated until the next planned outage. Neither outcome is ideal when you are trying to run a tight loop on pH or conductivity in a live process.
The SensoGate WA 130 is Knick's answer to that problem. It moves the sensor from the process stream into a sealed service chamber while the line stays live, rinses the probe mechanically before it is exposed, and prevents removal unless the fitting is in the correct position. This article sets out exactly how that works and what it means in practice for the operator standing at the line.
Two positions and what happens between them
The SensoGate operates in two positions: MEASURE and SERVICE. In the MEASURE position, the 225 mm sensor sits in the process stream, in direct contact with the medium. In the SERVICE position, the sensor has been pneumatically retracted into a sealed rinse and calibration chamber, separated from the process by the fitting's lock-gate seal, which closes automatically as the sensor withdraws and keeps the process reliably shut off in every position, even while the probe is moving. The drive is pneumatic, which means it works without electrical actuation at the probe end and is straightforward to integrate into a control system via a standard solenoid valve and position feedback.
The transition between positions is not simply a mechanical pull. As the sensor shaft retracts, an internal scraping ring wipes the shaft surface, removing the bulk of any process medium that has adhered to it. Once the sensor is seated in the service chamber, a patented cyclone rinse cycle flushes the residual medium from the shaft and chamber walls before the sensor is fully accessible. By the time the fitting signals SERVICE position, what the operator encounters is a rinsed sensor in a clean chamber, not a probe dripping with hot or hazardous process fluid.
A mechanical interlock enforces this: the sensor cannot be physically removed from the fitting unless the unit is confirmed in the SERVICE position. There is no manual override. This is an important safety detail, and one that we covered in depth when looking at the broader safety case for retractable fittings and the risks of changing a probe on a standard fixed holder.
How the fitting holds under pressure
The WA 130 is rated to approximately 6 bar (87 psig) line pressure across a temperature range of 0 to 140 degrees Celsius. That covers the majority of wet analytical measuring points in food and beverage, pharmaceutical production, water treatment and general industrial process chemistry. The pressure rating applies in both positions: the fitting maintains its seal whether the sensor is in the process or retracted into the service chamber.
The sealing geometry is designed around the scraping ring and the lock-gate working together. When the sensor withdraws, the scraping ring is the first seal; the lock-gate closes behind it as a hard process barrier. The SensoGate is the first retractable fitting to pair that lock-gate with a sealing water function, and the gaskets are rinsed during every stroke movement, from measurement to the service position and back, which reliably prevents dirt, fibres and particles from adhering to them. The cyclone rinse chamber sits between those two seals. This means that even before the rinse cycle completes, the process medium cannot travel further than the lock-gate, and the operator is not exposed to line pressure at any point during sensor removal.
For measuring points operating at the upper end of the temperature and pressure envelope, Knick offers the WA 130 H variant, which is engineered for hygienic conditions. The modular design of the wetted parts means the same mechanical platform covers a wide range of process chemistries without requiring a different fitting body.
Wetted materials: matching the fitting to the process
The surfaces that contact the process medium are modular and specified to the application. Standard options include PEEK, PVDF, polypropylene, stainless steel 1.4571 and Hastelloy. For pharmaceutical and food applications, all process-wetted parts including the rinse and calibration chamber are FDA certified. Carbon-fibre-reinforced plastic options are available for measuring points that combine higher mechanical demands with chemically aggressive media.
Selecting the right wetted material combination is not always straightforward. Chlorinated solvents, strong oxidising acids and certain food-grade cleaning agents each have different compatibility profiles, and a material that performs well in one duty can fail quickly in another. At DP-Flow we work through this at specification stage, not after the fitting has been installed. The modular architecture of the WA 130 means that if process chemistry changes, it is usually possible to swap wetted components rather than replace the entire fitting body.
Sensors the WA 130 carries
The fitting accepts standard 225 mm sensors across the analytical parameters: pH, ORP, conductivity and dissolved oxygen. It is compatible with both conventional analogue sensors and Memosens digital sensors. Memosens compatibility is worth noting because it changes how calibration is managed: with a Memosens sensor, calibration can be performed in the laboratory on a bench instrument, with the calibration data stored on the sensor head itself. The calibrated sensor is then fitted to the WA 130 and the transmitter reads the stored calibration data directly. There is no calibration step at the measuring point, and the replaced sensor carries a complete calibration history that transfers automatically.
For operations that run frequent sensor changes, this matters. The time at the measuring point is reduced to the sensor swap itself: retract, unclip, clip in the replacement, advance to MEASURE. The calibration work happens off-line, in a controlled environment, at a time that suits the laboratory rather than the production schedule.
The media adapter and central multi-plug
The SensoGate WA 130 uses a plug-and-play media adapter to connect the fitting to the rinse, cleaning and calibration media supply, as well as the control air line. All of these connections are made through a single central multi-plug, which simplifies installation significantly. There is one connection point to make when installing the fitting, and one to break when removing it for maintenance. The media lines, air supply and signal wiring do not need to be disconnected individually.
This is also the connection that links the SensoGate into a fully automated maintenance loop. The media adapter is designed for direct connection to the Unical 9000 or Uniclean 900 controller, which supplies the cleaning and calibration media under pneumatic control and manages the rinse, clean and calibrate sequences automatically. Once that connection is made, the SensoGate becomes the process end of a cCare loop.
From fitting to full automation
The SensoGate WA 130 is a competent retractable fitting on its own, but its real value in a process environment comes when it is connected to the rest of the Knick analytical system. Paired with a Unical or Uniclean controller and a Protos transmitter, it becomes the field element in a cCare automated sensor maintenance loop. In that configuration, the controller initiates the retraction, manages the cyclone rinse sequence, delivers the calibration buffers in the correct order, monitors the sensor response, calculates and applies the calibration, and returns the sensor to the MEASURE position, all without anyone at the line.
The implications for a measuring point in continuous production are significant. Calibration intervals are set by the process requirement and the controller executes them reliably, regardless of shift patterns, production pressure or whether anyone remembered to collect buffers. Sensor health data and calibration records pass back to the transmitter and from there, over fieldbus, to the control system. We looked at what that means for remote cCare operation from the control room via the Profinet module separately; the short version is that the operator does not need to go to the measuring point at all.
For an end-to-end view of how the SensoGate, cCare and the Protos II 4400 transmitter combine into a compliant automated loop, we set that out in the hub article for this series.
Working out whether the WA 130 fits your measuring point
The WA 130 is well suited to measuring points where the process medium is hot, pressurised, hazardous, or simply difficult to interrupt. If your current practice involves waiting for a shutdown to change a probe, or if operators are handling sensors that have just come out of a hot or chemically aggressive stream, a retractable fitting changes that risk profile materially. The engineering is mature and the safety interlock is unconditional.
Whether the WA 130 is the right variant, and which wetted material combination suits your process chemistry and temperature profile, depends on the specifics of the measuring point. The way to answer that properly is to look at the actual line conditions: pressure, temperature, medium, cleaning regime, and sensor type. At DP-Flow we work through that selection at specification stage, and we would rather specify it correctly once than troubleshoot a material compatibility issue after installation.