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Liquid Nitrogen Level Sensor (SI-807)
A capacitance liquid nitrogen level sensor for LN2, LOX, LAr and LNG storage and transfer tanks. The coaxial probe reads continuous level down to −196°C, outputs 4–20 mA (or 0–5 V / RS485), has no moving parts, and is built to length from 50 to 3000 mm.
- Detection length: 50 to 3000 mm (built to order)
- Medium temperature: −196 to +80°C
- Output: 4–20 mA / 0–5 V / RS485 / RS232
- Accuracy: 0.5 / 1.0 / 2.0 % FS
- Pressure: up to 1.6 MPa
- Principle: capacitance, continuous
Overview
The SI-807 is a capacitance liquid nitrogen level sensor built for cryogenic service. It measures the continuous level of liquid nitrogen (LN2), liquid oxygen (LOX), liquid argon (LAr) and LNG in storage and transfer tanks and dewars, from −196°C. Because it senses level by capacitance rather than by a float or moving part, it keeps working reliably at deep-cryogenic temperature. The probe is built to the tank height (50 to 3000 mm), gives a 4–20 mA, 0–5 V or RS485 output, and is available with an explosion-proof housing.
Features
Cryogenic to -196 C
Rated for LN2, LOX, LAr and LNG deep-cold service.
Continuous capacitance level
No float and no moving parts; high sensitivity and good linearity.
Built to length
Probe made 50 to 3000 mm to match the tank height.
4-20 mA and digital
4-20 mA, 0-5 V, RS485 or RS232 output.
Explosion-proof option
2088 Ex housing or 304 stainless micro-housing.
Wide supply voltage
DC 12-24 V standard, 5-36 V on request.
Working principle
The probe forms a coaxial capacitor. Liquid nitrogen has a dielectric constant of about 1.5, while nitrogen gas is about 1.0. As the liquid level rises, more of the gap between the electrodes is filled with liquid, so the measured capacitance increases. The transmitter converts that capacitance into a continuous 4–20 mA (or digital) level signal.
Technical specifications
| Item | Standard | Customizable |
|---|---|---|
| Operating voltage | DC 12–24 V | 5–36 V |
| Medium (detector) temperature | −196 to +80°C | Custom |
| Ambient temperature | −40 to +80°C | −40 to +80°C |
| Detection length | Per nameplate | 50 to 3000 mm |
| Pressure range | up to 1.6 MPa | Special order |
| Probe diameter | 16 mm | 8 to 25 mm |
| Process connection | M20x1.5 | M10–M30 / NPT / G / sanitary clamp |
| Housing / Ex | 2088 explosion-proof shell | 2088 Ex shell / 304 stainless micro shell |
| Accuracy | 1.0 / 2.0 % FS | 0.5 / 1.0 / 2.0 % FS |
| Output signal | 4–20 mA | 4–20 mA / 0–5 V / RS485 / RS232 |
Output and wiring
The standard build is a two-wire 4–20 mA loop on a DC 12–24 V supply, with an M20x1.5 process connection. Voltage (0–5 V), RS485 (Modbus) and RS232 outputs are available for digital display and monitoring, and a local display version reads level directly at the tank.
Applications
LN2, LOX and LAr storage and transfer tanks; cryogenic dewars and micro-bulk tanks; LNG tanks; air-separation plants; and cryopreservation and biobank vessels where the level of liquid nitrogen has to be monitored continuously.
Related products
Cryogenic Pressure TransducersPressure for LN2, LOX and LH2 at deep-cryogenic temperature.
Liquid Nitrogen Flow MeterFlow of LN2 and other cryogenic liquids.
Browse all capacitance level sensors →
FAQ
How does a capacitance liquid nitrogen level sensor work?
The coaxial probe is a capacitor. Liquid nitrogen (dielectric about 1.5) and nitrogen gas (about 1.0) fill the gap between the electrodes. As the level rises, more liquid fills the gap and the capacitance goes up; the transmitter turns that into a 4–20 mA level signal.
What temperature can it measure?
The detector is rated from −196°C (liquid nitrogen) up to +80°C, with the ambient electronics rated −40 to +80°C.
What output does it give?
Standard is 4–20 mA; 0–5 V, RS485 (Modbus) and RS232 are available, plus an optional local display.
Can the probe length be customized?
Yes. The probe is built to the tank height, from 50 to 3000 mm, with M20x1.5 or other process connections.
Request a quote
Tell us the cryogen, tank height, pressure and output you need and our engineers will size an SI-807 for you.
About this page. Written by the Instranova engineering team from the SI-807 datasheet. Specifications are representative; confirm the exact configuration against the datasheet for your application.