When a level switch in a well, sump or tank stops working, the consequences tend to show up quickly. A pump may run dry, a tank may overfill, or a reservoir may drop below its minimum without anyone being alerted. Level switches are among the simplest devices in a water system, but the jobs they protect are often critical, and the switch is frequently installed somewhere difficult to reach. The Paquin P108 Electronic Level Switch is an economical submersible level switch designed for exactly these conditions. It can operate at depths of up to 328 ft (100 m), needs no calibration, and can be configured so that a failure is never mistaken for normal operation.
How the P108 detects liquid
The P108 uses capacitive sensing. An insulated, coated electrode registers the change that occurs when it is surrounded by water or a water-based solution, and the switch output changes state in about 0.1 seconds. A slotted polypropylene crown surrounds the electrode, allowing liquid in while protecting the electrode from debris, contamination and physical damage. The crown is threaded, so it can be removed for cleaning when needed.
Because detection is electronic, there is no adjustment or calibration during installation. The P108 is ready to work as soon as it is wired and lowered into position, and it operates in any orientation.
A submersible level switch rated to 328 feet
Deep installations such as boreholes and wells place unusual demands on a sensor. The P108 is rated for immersion depths up to 328 ft (100 m), equivalent to 145 psi (1 MPa), and it carries an IP68 protection rating for continuous submersion.
- Corrosion-resistant construction. Both the housing and the protective crown are polypropylene, which resists corrosion in aggressive water and fluid media.
- Wide temperature range. The switch operates from -4°F to 176°F (-20°C to +80°C).
- Simple suspension. The P108 is installed from above and hangs by its cable. At approximately 0.44 lb (0.2 kg) without cable, it is easy to lower into narrow openings.
- Built-in electrical protection. The sensor is protected against electric shock at the electrode, reverse polarity, overvoltage and short-term current overload on the output.
Two-wire, no-calibration installation
The P108 is a two-wire device powered from 6 to 30 VDC. The supply is wired through the load, typically a relay coil. Alternatively, the P108 connects straight to a PLC binary input or an evaluation unit, in which case no separate load is needed. The output switches between 3.3 and 40 mA, and off-state current is limited to 0.6 mA. Capacitive loads and low-resistance loads such as incandescent bulbs are treated as a short circuit by the sensor's protection, so they should not be connected directly.
The standard cable is a two-conductor PVC cable (2 × 0.75 mm²), supplied to the length you specify in meters. Two practical recommendations from the datasheet are worth noting for long runs:
- Where strong electromagnetic interference is present, or where the cable runs parallel to power lines, use a shielded cable.
- For remote installations with long cables, add appropriate surge protection to the line.
The P108 also conforms to EN 55011 / B, EN 61326-1 and the EN 61000-4 series of electromagnetic compatibility standards listed in its datasheet.
Choosing NO or NC for fail-safe operation
The P108 is available with a normally open or normally closed output, defined as the output state when the switch is not immersed. Selecting the right option does more than set the logic. It determines how a failure will appear to your control system.
| Application | Recommended output | How it behaves |
|---|---|---|
| Minimum level (dry-run or low-level protection) | A: Normally open | Closes when immersed. If the level drops, or the sensor or wiring fails, the output opens and the alarm state is signaled. |
| Maximum level (overfill protection) | B: Normally closed | Opens when immersed, signaling that the maximum level has been reached. |
For minimum-level duty in particular, the normally open configuration means that a sensor or wiring failure looks the same as an emergency low level, so it cannot go unnoticed.
Applications
- Boreholes and wells
- Sumps
- Tanks and reservoirs
- PLC fluid control systems
- Skid packages
Key specifications (snapshot)
| Parameter | Value |
|---|---|
| Sensing principle | Capacitive, insulated (coated) electrode |
| Maximum immersion depth | 328 ft (100 m) / 145 psi (1 MPa) |
| Output | Two-wire; normally open (A) or normally closed (B) |
| Supply voltage | 6–30 VDC |
| Switched current | 3.3 mA min. to 40 mA max.; off state ≤0.6 mA |
| Remanent voltage (on state) | ≤6 V |
| Output time delay | 0.1 s |
| Ambient temperature | -4 to +176°F (-20 to +80°C) |
| Protection class | IP68 |
| Housing and crown | Polypropylene (PP) |
| Process connection | M18 x 1.5 metric thread |
| Electrode length | 30 mm |
| Cable | PVC, 2 × 0.75 mm², length to order |
| Weight (without cable) | Approx. 0.44 lb (0.2 kg) |
Dimensional drawings, the wiring diagram and the full parameter list are in the P108 datasheet (PDF).
Getting a P108 quoted
Specifying a P108 involves only two decisions: the output type (normally open or normally closed) and the cable length your installation requires. If you need a continuous level reading rather than a single switch point, the P110 Submersible Level Sensor measures to depths of up to 656 ft. The complete range of switches, floats and transmitters is in Paquin's level sensor collection.
Let us know where the switch will be installed. From the P108 product page, share the depth, the liquid, the cable length and whether you are protecting a minimum or a maximum level. A Paquin specialist will confirm the right output option and provide pricing.
New products and application notes from Paquin appear regularly on our LinkedIn page.