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A servo tank gauge is a device used to measure the level of liquid in a storage tank

A servo tank gauge (STG) is a high-precision instrument used to measure the liquid level, interface level, and density in storage tanks, particularly in industries like oil & gas, petrochemicals, and chemicals.

What Is a Servo Tank Gauge?

A servo tank gauge is a non-contact level measurement device that uses a servo motor mechanism to control the position of a sensing element (often a displacer or a float) suspended by a wire inside a tank. It provides real-time, high-accuracy readings of:

Liquid level

Interface between two immiscible liquids (e.g., oil and water)

Liquid density

Temperature (when integrated with a multi-spot thermometer)

How It Works:

A small displacer is suspended into the tank by a wire or tape connected to a servo motor in the gauge head.

The servo motor maintains the displacer at neutral buoyancy (constant tension).

By measuring the amount of motor torque or movement required to hold the displacer in place, the system can determine:

Liquid level (based on immersion depth)

Density (based on buoyant force)

Interface level (if there’s more than one liquid)

✅ Key Advantages:

Very high accuracy (±0.4 mm or better in modern systems)

Multi-variable measurement (level, interface, density)

Suitable for custody transfer and inventory management

Compatible with tank gauging systems (e.g., Rosemount, Honeywell Enraf, etc.)

Non-intrusive versions available for certain applications

Typical Applications:

Oil terminals and depots

Refineries

Chemical plants

Liquefied gas storage (LPG, LNG)

Custody transfer stations

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Grounding and overfill protection system connection between the railcar and the loading terminal

1. Grounding System (Electrostatic Discharge Protection)

Why grounding is needed:

When you load or unload flammable liquids (like fuel, chemicals) into or from a railcar, friction can build up static electricity.

If not discharged properly, a spark could occur — causing a fire or explosion.

How grounding works:

A ground cable is physically attached from the loading terminal’s grounding and overfill protection system to the railcar.

The grounding and overfill protection system checks that the railcar is properly bonded to the earth (resistance usually <10 ohms).

Loading will not start (or is immediately stopped) if grounding is not confirmed.

Equipment used:

Ground verification clamps with sensors

Ground monitoring units with automatic interlocks

Alarms and status indicators (green = safe, red = unsafe)

2. Overfill Protection System

Why overfill protection is needed:

Overfilling a tank can cause dangerous spills, vapors, and even explosions.

How overfill protection works:

The railcar is equipped with sensors or probes (high-level sensors) inside its tank compartments.

When product levels approach maximum safe capacity, the sensor sends a signal via a wired connection or wireless link to the terminal’s overfill protection controller.

If the product level hits the limit:

Automatic shutdown of pumps/valves.

Audible and visual alarms trigger immediately.

Typical equipment:

Overfill probes (float type, capacitive, ultrasonic)

Electronic rack monitors

Emergency shutoff valves

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The tank gauging system measures precise batches and custody transfers

A tank gauging system is a critical solution for accurately measuring liquid levels, volume, mass, and temperature in storage tanks. It’s essential for:

  • Precise batch measurements during blending or transfer
  • Custody transfer operations where legal and financial accountability is required

These tank gauging systems ensure compliance with industry standards such as OIML R85 and API MPMS, enabling accurate inventory control and transaction validation.

Key Functions

  1. High-accuracy level measurement (typically with radar or servo gauges)
  2. Temperature and density compensation
  3. Volume and mass calculations
  4. Real-time inventory monitoring
  5. Water bottom detection
  6. Interface with control tank gauging systems (SCADA, DCS)

Used In

  • Oil & gas terminals
  • Petrochemical plants
  • Bulk liquid storage farms
  • Refineries
  • Logistics hubs for fuels and chemicals
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Servo tank gauge with efficient inventory management

A Servo Tank Gauge  with efficient inventory management capabilities is a high-precision instrument widely used in tank farms, refineries, petrochemical plants, and terminals to measure and manage bulk liquid inventory — especially for custody transfer and critical stock control.

Let’s break down how an STG contributes to efficient inventory management:

What is a Servo Tank Gauge?

A Servo Tank Gauge uses a servo-driven motor to lower a sensing weight (or displacer) into the tank. It precisely measures:

Product level

Interface level (oil/water separation)

Density

Temperature (via integrated temperature sensors)

Real-World Benefits

Improved custody transfer accuracy = financial accountability

Reduced product loss through tighter reconciliation

Faster inventory decisions from real-time data

Automation-ready for unmanned terminals or remote tank farms

Forecasting and analytics via integration with inventory management software

Common Interfaces for Integration

HART

Modbus RTU/TCP

Foundation Fieldbus

Profibus

OPC DA/UA

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Monitors bottom loading of grounding and overfill protection system

Monitoring the bottom loading of grounding and overfill protection systems is critical in industries like fuel distribution, chemical handling, and hazardous materials transfer. These systems are designed to ensure safe loading operations by preventing static discharge and tank overfilling — two major causes of fire and environmental hazards.

What Is Bottom Loading?

Bottom loading refers to filling a tank (usually a fuel tanker or storage tank) from the bottom inlet rather than the top. It:

  • Minimizes static build-up
  • Reduces vapor release
  • Speeds up loading

Key Functions of a Grounding and Overfill Protection Monitoring System

✅ 1. Grounding Verification

  • Ensures the tanker or container is properly grounded before loading begins.
  • Monitors for continuity between the truck and earth ground.
  • Automatically interlocks loading system — it won’t begin unless grounding is verified.

✅ 2. Overfill Protection

  • Uses sensor probes inside the tank to detect product levels.
  • Alerts operators or shuts down flow when a preset fill level is reached.
  • Ensures compliance with API RP 1004 and EN 13922 standards for petroleum tankers.

✅ 3. System Interlocks and Alerts

  • Visual indicators (green/red lights) show safe or unsafe conditions.
  • Audible alarms alert in real-time.
  • May also provide relay outputs to control pumps, valves, or PLCs.

Integration With Automation Systems

Can be integrated with:

  • Terminal Automation Systems (TAS)
  • SCADA/PLC control systems
  • Batch loading controllers

Enables automated record-keeping, real-time safety feedback, and remote monitoring

Application Scenarios

  • Petroleum loading racks
  • Chemical tank farms
  • Aviation fuel depots
  • Railcar and truck bottom loading stations
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Instrumentation Oil Movement with Tank Gauging System

Great topic! Instrumentation for oil movement using a tank gauging system plays a key role in ensuring accurate, safe, and efficient measurement and control of oil during storage, transfer, and distribution processes in terminals, refineries, and petrochemical facilities.

✅ What Is Tank Gauging in Oil Movement?

A Tank Gauging System (TGS) is a measurement solution that monitors the level, temperature, volume, pressure, and density of liquids in storage tanks. In oil movement, it ensures accurate custody transfer and inventory management.

✅ Core Instruments Involved:

1. Level Gauges

  • Radar Gauges (e.g., Guided Wave or Non-Contact Radar)

Measure tank level with high precision.

Common in modern systems for oil storage tanks.

  • Servo Gauges

Provide ultra-precise level and interface measurements (often in custody transfer).

2. Temperature Sensors

  • Multi-spot RTDs (Resistance Temperature Detectors)

Monitor product temperature at different heights.

Crucial for volume correction and density calculations.

3. Pressure Sensors / Transmitters

Monitor vapor pressure or product pressure at the bottom of the tank.

Important in pressurized tanks or floating-roof tanks.

4. Tank Side Monitor (TSM)

Interfaces with field instruments and provides local display.

Transmits data to the central control system.

5. Automatic Tank Gauging (ATG) System

Collects, logs, and analyzes all tank data.

Interfaces with the plant’s DCS (Distributed Control System) or SCADA system.

✅ Key Benefits in Oil Movement:

Accurate Volume Measurement: Converts tank levels into standard volume using temperature and density data.

Safety: Prevents spills, overfills, and vapor emissions.

Inventory Control: Real-time tracking of stock levels and movement.

Custody Transfer Accuracy: Reduces disputes and ensures regulatory compliance.

Remote Monitoring: Enables centralized operations and quicker response times.

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Portable density meter with an ergonomic design

A portable density meter with an ergonomic design is a must-have for field or lab professionals who need quick, accurate measurements without the bulk of benchtop equipment. Here’s what to look for and a few top recommendations:

Key Features of an Ergonomic Portable Density Meter

✅ Ergonomic Design

  • Lightweight and compact: Easy to hold with one hand.
  • Rubberized or contoured grip: For long use without fatigue.
  • Tilted or intuitive touchscreen display: Improves readability during fieldwork.
  • Single-button or guided workflow: Makes operation smooth and efficient.

✅ Performance Specs

  • Measures density, and often specific gravity, concentration, or API gravity.
  • Temperature-compensated readings.
  • Accuracy typically around ±0.001 g/cm³ or better.
  • Fast measurement time (usually under 1 minute).

✅ Durability

  • Shock-resistant casing and IP-rated for dust or water resistance (IP54–IP67).
  • Battery-operated with long runtime and USB charging.

Where It’s Used

  1. Petroleum industry (API gravity, fuel testing)
  2. Food & beverage (sugar content, alcohol %)
  3. Pharma (solution concentration)
  4. Chemical plants & labs (reaction monitoring)
  5. Environmental monitoring (river water, effluent checks)
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Servo tank gauge for high accuracy liquid level measurement

A servo tank gauge (STG) is a highly precise instrument used for liquid level measurement in industrial tanks. It is commonly applied in oil, chemical, and LNG storage facilities where high accuracy, reliability, and compliance with international standards are required.

1. How a Servo Tank Gauge Works

A servo motor controls a displacer (sensor weight) that is suspended in the liquid. The gauge continuously adjusts the position of the displacer to maintain equilibrium, measuring the liquid level, interface, and density with high precision.

2. Key Features of Servo Tank Gauges

✅ High Accuracy – Measures liquid levels with millimeter precision (±0.4 mm or better).
✅ Multi-Parameter Measurement – Simultaneously measures level, density, and interface between two liquids.
✅ Continuous Monitoring – Provides real-time data for inventory management and process control.
✅ Automatic Compensation – Adjusts for factors like temperature, density changes, and tank movement.
✅ Compliance with Industry Standards – Meets API, OIML, and ISO guidelines for custody transfer and inventory control.
✅ Integration with Tank Gauging Systems – Works with SCADA, DCS, and inventory management software for remote monitoring.

3. Applications of Servo Tank Gauges

  1. Oil & Gas Storage – Measures crude oil, refined petroleum, and LNG in bulk storage tanks.
  2. Chemical Industry – Monitors liquids with varying densities and interfaces in chemical tanks.
  3. Marine & Bunkering – Ensures precise fuel measurement in ships and offshore platforms.
  4. LNG & Cryogenic Storage – Works in low-temperature environments with high accuracy.

4. Choosing the Right Servo Tank Gauge

  • Measurement Range – Select a gauge suitable for tank size and liquid type.
  • Accuracy Requirements – Choose high-precision models for custody transfer applications.
  • Explosion-Proof & Hazardous Area Certification – Essential for use in flammable liquid storage.
  • Integration with Other Sensors – Some models include temperature probes and pressure transmitters for complete tank monitoring.
  • Communication Protocols – Look for Modbus, HART, or Foundation Fieldbus compatibility for easy integration.
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Tank gauging system for inventory control and overfill prevention

A tank gauging system for inventory control and overfill prevention ensures accurate measurement of liquid levels in storage tanks while enhancing safety and operational efficiency. Here are key aspects to consider:

Types of Tank Gauging Systems

  • Servo Tank Gauges (STG) – High-precision systems like the Proservo gauge, ideal for bulk liquid storage, custody transfer, and high-accuracy applications.
  • Radar Tank Gauges (RTG) – Non-contact guided wave radar or free-space radar for real-time level measurement, suitable for crude oil, chemicals, and LNG tanks.
  • Hydrostatic Tank Gauging (HTG) – Measures liquid pressure at the tank bottom, used for mass-based inventory tracking.
  • Float & Tape Gauges – Traditional mechanical systems, reliable but less accurate than radar or servo gauges.

Key Features for Inventory Control & Overfill Prevention

  1. High Accuracy Measurement – Essential for custody transfer and precise inventory tracking.
  2. Temperature & Density Compensation – Provides corrected volume measurements to account for thermal expansion.
  3. Real-Time Monitoring – Integration with SCADA, DCS, or cloud-based systems for continuous data access.
  4. Overfill Prevention System (OPS) – High-level alarms and automatic shutdown functions to prevent spills.
  5. Redundant Alarms & Safety Compliance – Meeting standards like API 2350 for overfill protection.

Applications

  • Oil & Gas Terminals – Custody transfer and stock reconciliation.
  • Chemical Storage – Ensures safe handling of hazardous liquids.
  • LNG Tanks – Cryogenic applications with special radar systems.
  • Refineries & Petrochemical Plants – Inventory management for process optimization.