Paquin is spotlighting the P112 Compact Electronic Level Switch, a non-invasive level switch that detects liquid through the wall of plastic or glass pipes, tubes, tanks and vessels. It mounts on the outside of the container, so no hole is drilled and nothing touches the liquid. It works with both conductive and non-conductive media, including liquids that tend to cling to surfaces. At 25 × 40 mm and about 2 oz with 2 m of cable, it fits where conventional level switches cannot.
Why measure through the wall
Most point-level switches need an opening in the vessel: a threaded port, a flange or a fitting for a float. In plastic and glass containers, every added penetration is a potential leak path, and retrofitting a port into an existing tank can be impractical. Inserted sensors are also exposed to the process liquid, which matters for clean fluids, aggressive chemicals and media that leave deposits.
A through-wall switch avoids these issues. The vessel remains sealed, the sensor never contacts the liquid, and the switch can be repositioned or added later without draining or modifying the container.
How the P112 non-invasive level switch works
The P112 uses high-frequency sensing to detect the presence of liquid on the other side of a non-conductive wall. Its sensitivity is taught on site for the specific liquid and wall, so it can reliably distinguish the full and empty states. The maximum wall thickness depends on the medium:
| Medium | Maximum wall thickness |
|---|---|
| Conductive liquids (e.g. water and water solutions) | 8 mm |
| Non-conductive liquids with relative permittivity εr < 10 (e.g. oils, diesel) | 3 mm |
Suitable media include water, water solutions, diesel, oils, cooling liquids and some solvents. The container wall must be glass or plastic. Electrically conductive or antistatic-treated walls are not suitable.
Prismatic or planar: choosing a sensor face
Two sensor faces are available, matched to the shape of the container:
- Prismatic (refracted): a V-shaped face for gauge pipes and tubes from about 15 to 50 mm in diameter. It is attached with two plastic straps, with the cable pointing downward.
- Planar: a flat face for vessels with flat walls. It is bonded to a clean, degreased surface with double-sided adhesive tape and can be mounted in any orientation.
Both mounting kits are included: the magnetic pen, double-sided tape and two plastic straps ship with every P112. The contact surface may reach 194°F (90°C) with strap mounting, or 140°F (60°C) when the adhesive tape is used. Its own ambient rating spans -4 to 176°F (-20 to 80°C).
Teaching the switch in place
Setup takes two touches of the supplied magnetic pen on the sensor's "M" spot. A short touch (up to 2 seconds) and a long touch (at least 4 seconds) are applied, one with the vessel empty and one with it full. The order of the two touches decides whether the output works as NO or NC. This teach-in also sets the sensitivity for the specific liquid and wall, and it should be repeated if the liquid changes. Each unit ships set for water in normally open mode.
An orange LED shows the switching state. It also flashes quickly if a setting was not recognized, and slowly if the output is short-circuited.
Wiring to a PLC or relay
The P112 runs on 6–30 VDC and offers a choice of two outputs:
- PNP (open collector): switches up to 100 mA, with a supply current of no more than 7 mA when on
- 2-wire electronic switch: switches 3.3–40 mA in series with a relay coil or PLC input
The output is short-circuit protected, but capacitive loads and incandescent bulbs are not suitable. On the 2-wire version, each LED flash briefly switches the output for about 3 ms. The datasheet recommends setting PLC input filtering to ignore pulses shorter than this. For cable runs over 30 m, or near power lines, shielded cable is recommended.
Applications
- Water, oil, coolant and solvent containers
- HVAC and cooling systems
- Chemical processing
- Food and beverage production
- Pharmaceutical production
Key specifications (snapshot)
| Parameter | Value |
|---|---|
| Sensing | High-frequency, through plastic or glass walls |
| Maximum wall thickness | 8 mm (conductive liquids); 3 mm (non-conductive, εr < 10) |
| Sensor faces | Prismatic (pipes ~15–50 mm dia.) or planar (flat walls) |
| Outputs | PNP open collector (100 mA) or 2-wire (3.3–40 mA) |
| Supply voltage | 6–30 VDC |
| Switching frequency | Max. 1 Hz |
| Setup | Magnetic pen teach-in; NO or NC selectable |
| Ambient temperature | -4 to 176°F (-20 to 80°C) |
| Contact surface temperature | Up to 194°F (90°C); 140°F (60°C) with adhesive tape |
| Protection | IP67 |
| Housing | Polypropylene, 25 × 40 mm |
| Connection | PVC cable (length to order) or field-wireable connector |
Dimensions, wiring diagrams and LED codes are covered in the P112 datasheet (PDF).
Put a P112 on your vessel
For metal tanks, where through-wall sensing is not possible, the P108 submersible level switch offers a simple alternative. The complete Paquin level range covers continuous transmitters and non-contact sensors as well.
Ordering a P112 involves three choices: sensor face, output type, and cable or connector. Send us a description of your container through the P112 product page, including the wall material and thickness, the liquid and how the switch will be wired. Paquin will confirm suitability and provide a quotation.
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