1. Level Measurement Concepts & Techniques
Mukund Shiroya
RIL-Hazira

2. Why level measurement?
To know the inventory in the storage or process vessel for
Material stock identification
Prevention of overflow
Prevention of overload to the agitators
Prevention of under load to the agitators
Batch filling & emptying control
Operation at optimum level

3. Level Measurement Two methods of Level Measurement Direct Measurement
Direct Measurement uses methods such as
visual Inspection
displacement of float
Tuning fork etc
Inferential measurement
Inferential measurement uses methods such as
pressure head
time of flight etc
attenuation of radiation
Change in Capacitance of material
Photoelectric

4. Direct Level Measurement

5. Level Gauge
This is a visual method of measuring the level of fluid in a vessel.
A Graduated pipe is connected to a vessel. As the level of the fluid inside the vessel increases the level inside the tube will increase.
A visual inspection of the tube ill provide an indication of the level inside the vessel.
Vessel

6. Reflex / Transparent level indicators
Reflex level indicator
Transparent level

7. Magnetic Level Gauges
A float containing a magnet rises and falls with the liquid. As the float moves, this information is transferred to the indication rail mounted on the outside of the tube. The white and red indication flaps represent air and liquid level respectively.
Magnet System
Each of the colored flap contains a small magnet which rotates through 1800 when passed by the bar magnet within the float. The bar magnet design does not lose magnet field strength even at temperatures of 4500C guaranteeing continuous operation in the most extreme applications.

8. Float type Detectors
Most Float type detectors use the principle of loss in weight of a buoyant float to indicate the level of the fluid.
The Float is selected such that it is lighter than the fluid. As the level of the fluid rises the float rises. This is sensed by the electronics assembly to indicate the level.

9. Float type Detectors
The float carries a member having a magnetic coupling with a transducer element (coil, magnetic reed, or Hall-effect switch), that is mounted on the outside wall of the tank.
In some designs, the float mechanically links the switching mechanism through the sealing in the wall (e.g., bellows). The switching system can respond to the restraining force developed by a spring element connected to the float or by an actuator of a force-balance servo system.
Float-type sensors with magnetic coupling (a) or mechanical link (b). L = level,
1 = tank, 2 = liquid, 3 = float, 4 = magnet, 5 = magnetic armature, 6 = contacts,
7 = bellows, 8 = lever

10. Level Measuring Technologies
* Vibrating Element
In a vibrating-element level sensor, the oscillations of a member (paddle) are damped when it is immersed in the liquid. The attenuation of oscillations indicates that the liquid has reached the measured level. The oscillations are stimulated and sensed by electronic means.

11. Float type Detectors Advantages Simple & proven techniques
Unlimited tank height
Better accuracy (depending on the float type)
Low capital,maintenance cost
Disadvantages
Subject to wear, corrosion, mechanical failure
Getting stuck due to material clogging,deposition, material buildup

12. Indirect Level Measurement

13. Differential Pressure
Level can be inferred from the differential pressure ( head ) of the fluid inside the tank.
Advantages
economical and easy to install
Online checking & maintenance possible
Disadvantages
Solid level measurement not possible
Only clean fluid cal be measured
Density variation gives error
Choking of impulse tubes possible

14. Differential Pressure
Options on Differential pressure based level measurement :
Purge type instruments
The nozzle on the vessel is continuously purged by a medium acceptable to process & back pressure is measured at HP & LP tapping.
Used for fluid with suspended particles or having crystallizing nature
Chemical seal type instruments
The nozzle on the vessel is flange type instead of threaded type.
Used when medium can chock the tapping
Cost of instrument is three times the conventional inst.

15. Time of flight - Ultrasonic
Ultrasonic instruments determine level by measuring the length of time it takes for a sound pulse to return to a piezoelectric transducer after bouncing off the process material.
The sensor uses high-performance Piezoelectric crystals to generate short ultrasonic pulses in the form of sound waves. These pulses are directed toward a specific target from where they get reflected back to the transducer which acts as transmitter/receiver.
The transit time taken to receive the reflected pulse is measured by the electronics.
d = Velocity of sound * time to travel
Level X = L-d d L

16. Time of flight - Radar
Radar-based devices beam microwaves at the process material's surface. A portion of that energy is reflected back and detected by the sensor. Time for the signal's return determines the level.
Radar provides a non contact sensor that is virtually unaffected by changes in process temperature, pressure or the gas and vapor composition within a vessel. In addition, the measurement accuracy is unaffected by changes in density, conductivity and dielectric constant of the product or by the air movement above the product.

17. Nucleonic Level measurement
This technique utilizes the attenuation of radiation taking place while it passes through physical matter, to indicate the level inside a vessel.
The assembly consists of a Radioactive source which emits radiation and a detector which detects the attenuated radiation and converts it into a percentage of actual level
I = I0*e-d

18. Nucleonic Level measurement
Type of Radioactive detectors
Geiger Counter
The most common radiation detection instrument is the Geiger counter. This instrument is a gas-filled detector that works on the principle that as radiation passes through air or a specific gas, ionization of the molecules occur. When a voltage is connected across the gas chamber, a current will flow as the positive ions are collected at the cathode and the negative ions are collected at the anode. This current can be used to power a meter to quantify the radiation.
The GM detector is a good sturdy detector used for the detection of beta and gamma radiation. It will detect most beta, gamma, and x-ray radiation used in the research environment as well as the strong gamma and x-ray radiation used in industrial radiography.

19. Nucleonic Level measurement
Scintillation Detectors
Scintillation crystals and photo-multipliers are used to detect and measure gamma and x-ray radiation. These detectors are especially useful in the research environment for detecting the low-energy photons emitted from I-125. The detectors can either be hand-held or well- counters. The well-counters are used to count samples in a low background shielded cavity

20. Nucleonic Level measurement
Actual Instrument :
Continuous Detector :
Extremely rugged and reliable even in harsh environments. The LJC is a continuous level detector utilizing ion-chamber technology.
Features & Benefits:
- Available in ranges up to 19 feet (6 meters)
- Frequency output to the Ohmart/VEGA Smart Pro, Pro Pac, or to a PLC/DCS
Applications:
- Standard vessels & tanks
- Areas in need of a rugged detector housing

21. Nucleonic Level measurement
Advantages of Neuclonic Instruments :
Low Maintenance & High Reliability
Non invasive to vessel No exposure to corrosion, abrasive, high pressure or high temperature process conditions
No moving parts Detectors employ no moving parts to wear, bind, corrode or fail on process
Proven technology Nuclear measurements have proven reliable over time in thousands of applications

22. Nucleonic Level measurement
Low Installation Cost
Gauge installed without process shutdown No alterations are required to the vessel interior for gauge installation in a standard application
No intrusions in to the vessel required With no intrusions necessary in a standard installation, no changes to coded vessels required
High first time success rate With nuclear level systems, there is a high success rate on the first installation. Time and money are not wasted trying multiple level technologies

23. Nucleonic Level measurement
Solves Difficult & Extreme Applications
High temperature Process temperature has no effect on measurement
High pressure or vacuum Measures in all process pressures
Corrosive Non contact technology allows use in the most aggressive services
Volatile or biohazard Non invasive nature eliminates process connections and leak paths
Agitators, baffles, coils & other obstacles Internal obstructions are inconsequential to the measurement with properly configured systems
Build up on vessel interior Process build up upon the vessel interior can be compensated for by special gauge configurations

24. Photoelectric
Photoelectric level sensors operate in transmittance or reflection modes. In the transmittance mode, a sensing system, including a light beam source and a photo detector, responds to the interruption or the attenuation of the light beam when the liquid breaks the beam path from the source to the detector. In the reflection mode, an optical prism mounted inside a tank changes the reflectance of the light when it is immersed in the liquid. The construction of the transducer is arranged so that a light source and photo detector for sensing the change in the light's intensity are mounted on the outside wall of the tank. The light beam passes through and is reflected from the faces of the prism.
Transmittance-mode (a) and reflectance-mode (b) photoelectric level sensors. L = level, 1 = tank, 2 = liquid, 3 = light source, 4 = photodetector, 5 = prism.

25. Capacitive-Level Sensors
Radio frequency (RF), based on capacitance or admittance, can handle a wide range of process conditions. Process temperature and pressure are limited only by the material of the sensing element. Level transmitters of this type sense the change of electrical impedance that occurs with the change of level on the sensor. RF devices ignore material buildup on sensor and work with all types of process material. It is an intrusive technology.

26. Typical examples of loops
Typical Measurement Loop
Transmitter
Control System
Process
Sensor

27. Typical examples of loops
Typical Control Loop
Transmitter
Control System
Process
Sensor
Final Control Element

28. Thank You