Mastering Measurement Methods

tube

liquid

head

13.85 inches

accurate

vessel

tare

Weight

located

mechanical

Mechanical

load

cell

either

contents

Formulas

Formulas

Formulas

Question 1

Question 1

transmitter

Question 1

10 ft2

Measured Wt (lb) – Tare Wt (lb)

3500lb – 1500 lb= 2000 lb

Volume (cubic feet) = V= 2000 lb 37 lbs/ft3

Density (lbs/ft3) V = 54.05 ft3

1. Level (feet) = 54.05 ft3 L= 10 ft2

Volume (cubic feet) Surface Area (square feet) L = 5.405 ft 5.405𝑓𝑡 −0 𝑓𝑡 ( )16 mA 8𝑓𝑡 + 4mA = 14.81 mA

If we used Mercury instead of wheat, with a density of 848 lb/ft3, what would its height be.

What is the approximate height of the mercury in the tank. V = 2000lbs/848 lb/ft3 V = 2.36 ft3 L = 2.36 ft3/10 ft2 L = 0.23 ft yes that is about ¼ of a foot (3”).

Paddle Wheel Detector Typically used granular or powered materials Paddle rotates until materials restricts rotation Direct, invasive, point measurement

This type of level measurement is based on the weakening of gamma radiation as it penetrates materials. The radioactive isotope is installed in a container, also referred to as shielding, which emits the radiation only in one direction. The source container and the transmitter used to detect the radiation are mounted on opposite sides of a vessel or pipe. The higher the level of the process in the vessel the lower the intensity of the radiation received. For example, at 50% of the full range level, only half of the detector receives the radiation. Why and where would we use nuclear measurement.

Electronic Sensors Ultrasonic Sensors Ultrasonic sound waves are transmitted, and the time required for the return echo is measured. The length of time determines the distance from the transceiver. No moving parts promote long life. Like sonar used for underwater depth detection but sound wave are above the human hearing range. Indirect, non-invasive, continuous measurement

Radar Sensors Similar in principle to ultrasonic, but uses high frequency radio waves instead of sound Ideal for applications with poor conditions such as foamy materials Indirect, non-invasive, continuous measurement

Conductive Probes Rods are suspended in an electrically conductive material and a circuit path will form between the rods Several rods can be used for multiple point levels Direct, invasive, point measurement.

Capacitive Probes A rod is suspended in non-conductive material to be measured and the capacitance between the rod and the vessel wall is measured. As the material level rises, a decrease in capacitance will be measured. Indirect, invasive, continuous measurement.

Differential Pressure Level Detector Same as a hydrostatic pressure system but used with a sealed and pressurized tank. Differential pressure transmitter has two pressure ports: wet leg (high pressure, bottom of vessel) and a dry leg (low pressure, top of tank)

DP Transmitter with Manifold D

Druck Pressure Calibrator

Differential Pressure Level Detector Measures the difference in pressure between the top of a pressurized tank, and the head pressure in the bottom of the tank. Placement of the transmitter is critical to the calibration of the transmitter. Indirect, invasive, continuous measurement

Differential Pressure = ΔP ΔP= High Pressure - Low Pressure Pressure = 0.433 x H x SG

Question: A pressurized tank 30‘ tall containing water has a wet leg pressure of 20psi and a dry leg pressure of 8psi. The weight density of the Hi-Quality water is 60.4 lb/ft3, what would the water level be in feet.

Solution: ΔP = Hl – LO = 20-8 = 12 psi SG= 𝑥 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 62.4 = 60.4 62.4 ΔP =khsg H= 12 0.433 𝑥 0.968 =28.63ft

Same question BUT we have the level but not the dry leg

Mechanical Springs = Located under each leg of a vessel or the vessel is suspended by them Load Cells = Convert a force such as tension, compression, pressure, or torque into an electrical signal Weight Method = Considered an indirect and non-invasive method Tare Weight = The empty vessel weight

Load Cell = A type of transducer that converts a force into an electrical signal Single point Load cell = A type of load cell that is commonly used Indirect Method = A method in which weight is used to calculate the level for solids and liquids Content Weight = The weight of the vessel and its contents

$Content Wt(lb) = Measured Wt (lb) – Tare Wt (lb)$ = Content Weight $Volume (cubic feet) = Density (lbs/ft^3) Volume (cubic feet)$ = Volume $Level (feet) = Surface Area (square feet) Area=πr^2$ = Level $Area=πr^2$ = Area

Rotational Suppression Method = Typically used for granular or powered materials, direct, invasive, point measurement Nuclear Level Measurement = Based on the weakening of gamma radiation as it penetrates materials, indirect, non-invasive, continuous measurement Electronic Sensors = Ultrasonic Sensors: Ultrasonic sound waves are transmitted, and the time required for the return echo is measured. Radar Sensors: Similar in principle to ultrasonic, but uses high frequency radio waves instead of sound. Conductive Probes: Rods are suspended in an electrically conductive material and a circuit path will form between the rods. Capacitive Probes: A rod is suspended in non-conductive material to be measured and the capacitance between the rod and the vessel wall is measured Differential Pressure Method = Measures the difference in pressure between the top and bottom of a pressurized tank, indirect, invasive, continuous measurement

$Area=10 ft^2$ = Content Wt (lb) = Measured Wt (lb) – Tare Wt (lb) $V=2000 lb/37 lbs/ft^3$ = Volume (cubic feet) = $V=2000 lb/37 lbs/ft^3$ $L = 5.405 ft$ = Level (feet) = $L = 5.405 ft^3$ $V = 2.36 ft^3$ = If we used Mercury instead of wheat, with a density of 848 lb/ft3, what would its height be.

Content Weight (lbs) = The weight of the material being measured in the vessel Tare Weight (lb) = The empty weight of the vessel Measured Weight (lb) = The total weight of the vessel and its content Density (lbs/ft3) = The mass per unit volume of a substance

Bubbler System = One of the oldest types of level measurement, used for liquid and fine powders Constant Differential Pressure Relay = A very accurate regulator used in the Bubbler System Load Cells = Alternative to Mechanical Springs, can be located at the base of the tank or above it Tare Weight = The empty weight of the vessel or tank, subtracted from the measured weight to get the content weight

$968 = 12 psi \Delta P = Hl - LO$ = Equation for calculating the differential pressure in the Bubbler System $LO = 20psi - 12psi = 8psi$ = Equation for calculating the backpressure in the Bubbler System $27.72$ water is $1$ psi = Conversion factor used in the Bubbler System $\frac{1}{2}$ psi change can represent over $13.85$" of level change = Relationship between pressure change and level change in the Bubbler System

Advantages: Not affected by foaming, conductivity, solids. Reliable because only part in contact with process is a tube. Self clean, Can be used for many different types of processes, such as slurries, corrosive, acidic or radioactive. Cost effective and relatively easy to configure = Bubbler System Disadvantages: Essential to maintain a constant supply pressure. Hole in dip tube. Turbulent process will affect reading = Bubbler System Advantages: Direct measurement, accurate, simple to install and maintain. Independent of process conditions. Can be used for many processes. Can be used for both liquids and solids. Can be used in all types of vessels = Load Cells Disadvantages: High initial cost. Not suitable for high pressure or high temperature applications = Load Cells

Differential Pressure Method = Method considered indirect and non-invasive Electronic Sensors = Type of level measurement that provides an output signal Mechanical Springs = Used under each leg of a vessel in the Weight Method Nuclear Level Measurement = Method used for measuring levels of liquids and fine powders