What Is the NSD Optical Level Switch?
The NSD is an optical level switch that provides solid-state point level detection in clear, translucent, and non-coating low-viscosity liquids. It uses an infrared optical sensor with no moving parts, a 316 stainless steel body, and a PNP open-collector output, and it is designed for OEM and general point level control applications.
The switch installs in any orientation through a 3/8 inch NPT fitting and signals a single point level as liquid rises to or falls away from the sensing tip. A red LED status indicator lights when the switch is activated, and the circuit is protected against overcurrent and reverse polarity.
How the NSD Detects Liquid
The NSD works by detecting the difference in refraction between liquid and air. An infrared LED inside the lens transmits a beam of invisible light. In air, the beam reflects back to an infrared receiver inside the sensing circuit. In liquid, the beam refracts away from the receiver, and the switch changes state.
This principle, based on total internal reflection at the lens tip, lets the NSD sense level with no floats or moving parts. Because detection depends on light passing through a clean lens, the NSD is intended for clear, translucent, low-viscosity liquids and is not recommended for emulsions, phase-change liquids, organic solvents, or highly viscous or coating liquids that can film the lens.
Materials and Media Compatibility
The NSD has a 316 stainless steel body with a polyethersulfone lens, and it is rated for low-viscosity, clear, translucent, non-coating liquids that are chemically compatible with these wetted materials. Installation orientation is universal, so the sensor can be mounted in the top, bottom, or side of a tank.
Specifications
The NSD carries a maximum operating pressure of 580 PSIG (40 bar) and an operating temperature range of 15 to 250°F (-9 to 121°C). It runs on a 10 to 28 VDC supply, switches loads up to 100 mA, and is built to an IP67 ingress protection rating. The process connection is a 3/8 inch NPT thread, with optional fittings available on request.
- Body material: 316 stainless steel with a polyethersulfone lens
- Maximum pressure: 580 PSIG (40 bar)
- Operating temperature: 15 to 250°F (-9 to 121°C)
- Power supply: 10 to 28 VDC
- Maximum switch load: 100 mA
- Output: PNP open collector, normally open or normally closed dry logic
- Ingress protection: IP67
- Process connection: 3/8 inch NPT (optional fittings on request)
- Overall length: 2.67 in (67.8 mm) with a 0.75 in (19 mm) hex
- Cable: PVC-jacketed, 24 AWG, 3-conductor
Output and Wiring
The NSD provides a PNP open-collector output available in two dry switching logics: normally open (de-activated) or normally closed (activated), selected by model code. The three-conductor cable wires the brown lead to the positive supply, the blue lead to the negative supply, and the black lead through the load. A red LED lights when the switch is activated.
Installation Requirements
The NSD threads into a 3/8 inch NPT port and can be mounted in any orientation. Apply a suitable thread sealant, such as PTFE liquid or tape, before installation, and tighten to a maximum of 8 lb-ft (10.8 N·m). Keep the sensing tip at least 1.2 in (30.5 mm) from any reflective surface, tank wall, or other physical interference.
Do not install the sensor near other infrared sources. Clean the lens periodically using compatible methods, and avoid organic solvents or scrubbing that could scratch the lens surface.
Applications
The NSD is used for single-point level control in tanks and small vessels. In liquid level control, upper and lower switches can start and stop a pump to hold liquid between two set points. In pump or motor protection, a low-level switch can signal a controller to help prevent dry running when liquid falls below the sensor.
Ordering the NSD
NSD model codes follow the pattern NSD-56-AU-P0 or NSD-56-AU-P1. The 56 designates the 316 stainless steel body, AU designates the 3/8 inch NPT process connection, and the final code sets the output: P0 for PNP normally closed dry and P1 for PNP normally open dry. Alternate fittings, outputs, and electrical connections are available on factory consultation, with a 25-piece minimum for non-standard configurations.
Common Questions about NSD - Economical Optical Level Switch
An optical level switch senses light. Inside the NSD lens, an infrared emitter sends invisible light toward the tip. When the tip sits in air, total internal reflection returns the light to a receiver. When liquid wets the tip, light escapes into the liquid, the receiver sees the change, and the output switches.
The NSD suits clear, translucent, non-coating liquids of low viscosity that are chemically compatible with 316 stainless steel and a polyethersulfone lens. It is not recommended for emulsions, phase-change liquids, organic solvents, or thick or coating liquids that leave a film on the lens and block the light path.
The NSD withstands pressures up to 580 PSIG (40 bar) and operates from 15 to 250°F (-9 to 121°C). Confirm that the process pressure and the liquid temperature at the sensing point both stay within these limits for the wetted materials before installation.
The wetted parts are 316 stainless steel for the body and polyethersulfone for the lens. This combination handles many common liquids, but the liquid must be chemically compatible with both materials. Optical sensing needs a clear lens, so the media should not coat or film the tip.
The output is a PNP open collector offered in two dry logics: normally open or normally closed, set by the model code. Wiring uses three conductors: connect brown to positive (+), blue to negative (-), and route the black lead through the load. A red LED lights when the switch activates.
The NSD runs on a 10 to 28 VDC supply and switches loads up to 100 mA. The circuit includes overcurrent and reverse-polarity protection. Size the connected load so that switch current stays within the 100 mA maximum, and provide a stable DC source within the rated voltage window.
Thread the NSD into a 3/8 inch NPT port in any orientation, seal the threads with PTFE liquid or tape, and tighten to no more than 8 lb-ft (10.8 N·m). Keep the tip at least 1.2 in (30.5 mm) from tank walls or reflective surfaces, and away from external infrared sources.
NSD codes read as NSD-56-AU-Px. The 56 marks the 316 stainless steel body, AU marks the 3/8 inch NPT connection, and the last field sets output logic: P0 is PNP normally closed dry, P1 is PNP normally open dry. A sample order code is NSD-56-AU-P1. Non-standard options are available on factory consultation, with a 25-piece minimum.
Typical uses include single-point level control and pump protection in tanks and small vessels. Paired upper and lower switches can start and stop a pump to keep liquid between two levels, and a single low-level switch can help prevent a pump from running dry when the vessel empties.
Product Specifications
Suitable Media
Compatible Low-Viscosity, Clear and Non-Coating Liquids
Electrical Protection
IP67
Temperature Range
15°...250 °F (121 °C)
Product Features
PNP Open Collector Output Standard
Low Cost and Reliable Optical Sensing Technology
Overcurrent and Reverse Polarity Protected
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