# What is "liquid level sensor packaging"?

**URL:** <https://forum.ofscn.net/t/what-is-liquid-level-sensor-packaging/2489>\
**Category:** OFSCN Technical Knowledge Base\
**Tags:** fbg-technology\
**Created:** [August 4, 2026, 2:14pm UTC](https://forum.ofscn.net/t/what-is-liquid-level-sensor-packaging/2489 "2026-08-04T14:14:24Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![VoidWalker](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/v/848f3c/32.png) [@VoidWalker](https://forum.ofscn.net/u/VoidWalker)\
**Post date:** [August 4, 2026, 2:14pm UTC](https://forum.ofscn.net/t/what-is-liquid-level-sensor-packaging/2489/1 "2026-08-04T14:14:24Z")

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How to use a row of temperature sensors to measure the liquid level in an oil tank?

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**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\
**Post date:** [August 4, 2026, 2:15pm UTC](https://forum.ofscn.net/t/what-is-liquid-level-sensor-packaging/2489/2 "2026-08-04T14:15:24Z")

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The basic principle of using a row of temperature sensors (temperature sensor array) to measure the liquid level in oil tanks is the **Temperature Gradient Sensing Method**.

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### I. Physical Principle and Measurement Mechanism

Inside large oil tanks or storage tanks, the medium usually exhibits distinct phase stratification (e.g., upper gas/oil vapor space, lower liquid oil, and potential sediment water at the bottom).

1. **Thermal Property Differences at Interfaces**  
Gases and liquids have significant differences in heat capacity, thermal conductivity, and thermal diffusivity. Under natural conditions (due to solar radiation, diurnal temperature variations, or heating/cooling processes of the medium within the tank), there is typically a continuous temperature difference \Delta T between the liquid phase and the gas phase inside the oil tank.

2. **Temperature Distribution and Gradient Localization**  
A row of temperature sensors is arranged longitudinally at equal or fixed intervals in a vertical direction (perpendicular to the liquid surface) inside the oil tank, forming a vertical temperature monitoring distribution curve:

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### II. Engineering Implementation and Sensing Technology Solution

In large industrial oil tanks (such as crude oil tanks, refined oil tanks), the environment is typically classified as a flammable and explosive area. Therefore, using a passive, intrinsically safe explosion-proof **quasi-distributed Fiber Bragg Grating (FBG) Temperature Sensor Array** is a technically advantageous solution.

#### 1. Measurement Point Layout and Spatial Resolution

- **Sensor String Arrangement** : Multiple Fiber Bragg Grating (FBG) temperature sensing points are packaged within a single protective tube at preset spatial intervals (e.g., \Delta z = 10\text{cm} or smaller) and suspended vertically inside the oil tank.
- **Interpolation Algorithms** : Based on the real-time temperature data collected from each measurement point, higher-order polynomial interpolation or spline interpolation is used to generate a continuous vertical temperature profile, thereby enabling the liquid level resolution to exceed the physical measurement point interval limitation.

#### 2. Technical Product Implementation

In fiber optic sensing applications, multi-point FBG temperature sensors encapsulated in steel tubes are typically used to measure the longitudinal temperature distribution. For example, the [OFSCN® 300°C Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/temperature-sensor-300.html) or [OFSCN® 100°C Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/temperature-sensor-100.html) utilizes seamless stainless steel tubes for sealed protection. Multiple FBG temperature sensing points can be integrated into a single sensor, offering corrosion resistance, pressure resistance, and intrinsic safety explosion-proof characteristics.

 ![OFSCN® 300°C Fiber Bragg Grating Temperature Sensor](https://forum.ofscn.net/uploads/default/original/1X/74932c0f3b71797adb12ca84a053059151051842.jpeg)  
 ![OFSCN® 300°C Fiber Bragg Grating Temperature Sensor](https://forum.ofscn.net/uploads/default/original/1X/890e8bb137088d916b6145a3bd3543febc968fd1.jpeg)

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### III. Technical Features and Considerations

1. **Intrinsically Safe Explosion-Proof Characteristics** : Fiber optic sensors rely on light signals for transmission. The optical fiber itself is non-conductive and does not generate sparks, making it extremely suitable for flammable and explosive environments such as oil storage tanks.
2. **Multi-Phase Interface Identification (Oil/Gas/Water)**: Due to differences in specific heat capacity and temperature between water and oil, this method can not only identify the “oil-gas” interface (liquid level) but also further identify the “oil-water” interface (interface level) at the bottom of the tank.
3. **Dependence on Environmental Temperature Difference** : The interface temperature gradient method relies on the temperature difference between the gas and liquid phases. When the medium in the tank and the gas at the top are in complete thermal equilibrium ( \Delta T \approx 0 ), the interface can be identified by combining it with a micro-heat source pulse heating method (self-heating measurement) or by relying on the diurnal natural temperature difference to re-establish the thermal gradient.