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Selecting the appropriate flow technology for your application
Flow sensors and flow meters are devices used to measure both liquid and gas flows in various process control applications. Most flow sensing applications can be broken down into two main groups: switching applications and metering applications. Depending on your application needs, choosing the right flow sensing technology will provide the best results for measuring gas and/or liquid flow.
Quick Reference Chart
| Sensor | Type of application | Output | Price | SI flow sensor
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Switching output, mounts in process | - Solid-state flow sensor with no moving parts that can wear or break in process
- Calorimetric flow technology
- Mounts directly in the medium to sense the flow of liquid or gases
- Pushbutton setup and stainless steel RTD
- AC and DC versions
| | Switching | Starting at
$279.00 | SF remote flow sensor
with control monitor |
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Switching output, two-piece design | - Two-piece flow system that provides remote indication of fluids and gases
- Calorimetric flow technology
- Industrial, aggressive media and hazardous locations
- Control monitor indicates flow and wire-break monitoring on LED display
- AC and DC versions
| | Switching | Starting at
$557.00 | SL air flow sensor
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Switching output for ventilation systems | - Flow sensor specifically designed for air flow monitoring in air ducts and ventilation systems
- Calorimetric flow technology
- Provides early warning of clogged filters
- Visual LED indication for flow above/below setpoint
- AC and DC versions
| | Switching | Starting at
$154.00 | SU ultrasonic
flow meter
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Monitor water, oil and glycol | - In-line flow meter simultaneously monitors flow rate, fluid temperature and volume
- Ultrasonic flow technology
- Water, oil and glycol applications in pipe diameters 1” and less
- Pushbutton setup and numeric display
- DC transmitter provides continuous indication
| | Analog,
pulsed and
switching output | Starting at
$634.00
| SM magnetic
inductive flow meter  |
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Monitor conductive media (>20μS/cm) | - In-line flow meter simultaneously monitors flow rate, fluid temperature and volume
- Magnetic inductive flow technology
- Monitors all conductive media (>20μS/cm) up to 6 gal/min
- Pushbutton setup and numeric display
- DC transmitter provides continuous indication
| | Analog,
pulsed and
switching output | Starting at
$450.00 | Metris flow meter
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Monitor air and gas for leaks | - In-line flow meter monitors compressed air and specialty gases (Ar, CO2, N2)
- Calorimetric flow technology
- Detects leakage areas to improve energy efficiencies
- Pushbutton set-up and numeric display
- DC transmitter provides continuous indication
| | Analog,
pulsed and
switching output | Starting at
$652.00 |
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CALORIMETRIC FLOW TECHNOLOGY
Flow sensors for switching outputs
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 | | | SI Flow tip design | | Principle of operation
The operating principle of ifm flow sensors is based on the calorimetric principle. ifm flow sensors use the cooling effect of a flowing fluid or gas to monitor the flow rate. The amount of thermal energy that is removed from the tip determines the local flow rate. This temperature-based operating principle can reliably sense the flow of virtually any liquid or gas.
The sensor tip houses two transistors and a heater element. One transistor is located in the sensor tip, closest to the flowing fluid. This transistor is used to detect changes in the flow velocity of the liquid or gas. The second transistor is bonded to the cylindrical wall and is affected only by changes in the temperature of the liquid or gas. The transistors are positioned like this to place them in close contact with the wall of the sensor probe, and at the same time, to keep them widely separated from each other within the confines of the probe.
 | Thermography of flow
monitor with no flow |  | Thermography of fluid
or gas flowing |
In order to make the sensor sense flow, it is necessary to heat one of the transistors in the probe. When power is applied, the tip of the probe is heated. As the fluid starts to flow, heat will be carried away from the sensor tip. Cooling of the first transistor is a function of how fast heat is conducted away by the flowing liquid. The difference in temperature between the two transistors provides a measurement of fluid velocity past the sensor probe. When fluid velocity is high, the temperature differential is small. As fluid velocity decreases, there is an increase in temperature differential.
SI Series flow sensors
For switching applications, ifm offers a solid-state flow sensor with pushbutton setup to detect the flow rate of a flowing fluid or gas. The one-piece sensor includes an LED status display and stainless steel RTD probe in a compact unit. The probe is inserted directly into the medium. With no moving components, there are no pieces to stick or break in the process. Application parameters are set using the microprocessor-based pushbutton setup. The sensor detects when the flow rate falls above or below the flow setpoint.
Applications include: flow detection of all fluids (liquids and gases).
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| | For technical information, click here:
SI5 Series DC switching output SI5 Series AC relay output SI5 Series DC analog output |
SF Series remote mount flow sensors
The SF Series flow sensor and control monitor is a two-piece system for remote indication of fluids and gases. This combination is ideal for environments that do not permit local installation of the control
monitor such as high temperature extremes or in applications where space is limited.
ifm offers models for aggressive media applications that provide excellent chemical compatibility. An FM approved explosion-proof sensor for hazardous areas is also available. Both control monitors provide flow, temperature and wire-break monitoring. The LED bar graph display provides visual indication of flow.
Applications include: remote monitoring flow detection of all fluids (liquids and gases), aggressive media and hazardous locations.
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| | For technical information, click here:SF Series remote mount flow sensorsSF Series mount ceramic flow sensorsSF Series explosion-proof sensors |
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SL Series air flow sensors for ventilation systems
The SL Series air flow sensor is specially designed for air flow monitoring in air ducts and provides early warnings of clogged filters. Its compact housing style fits easily into ventilation systems and features an adjustable potentiometer to establish a setpoint. An LED provides visual indication when flow is above or below the setpoint.
Applications include: flow in air ducts, early warning of clogged filters, ventilation system monitoring.
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| | For technical information, click here:SL Series DC or AC/DC relay output |
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ULTRASONIC FLOW TECHNOLOGY
Flow meter for metering applications
 | | | Piezoceramic sound transducers transmit and receive sound pulses | | Principle of operation
Ultrasonic technology is based on the differential transit time principle. Sound pulses are alternately emitted and detected with and against the direction of flow using piezoceramic sound transducers. The flow rate is calculated from the difference of the transit time – the time it takes for the sound wave to be transmitted and received. The ultrasonic flow sensor
The SU Ultrasonic Flow meter is designed to simultaneously monitor flow rate, detect fluid temperature and provide a totalizer function for a variety of water, oil and glycol applications. With its compact design, the ultrasonic flow meter is intended for small diameter pipes - 1” or less. The meter provides a four-digit numeric display of the liquid’s flow rate (gal/min or l/min), total quantity accumulated (gallons or liters), and medium temperature (°F or °C). The setpoints are established through a simple pushbutton setup. The meter can be programmed to provide switching output (flow rate and/or temperature), pulse output (flow volume), or analog output (flow rate or temperature).
Applications include: water applications with flow rates up to 26 gpm, high flow rates, water, oil and glycol solutions.
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| | For technical information, click here:SU Series switching, analog or pulse output
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MAGNETIC INDUCTIVE FLOW TECHNOLOGY
Flow meter for metering applications
 | | | Rollover to enlarge | | Principle of operation
A magnetic flow meter is a volumetric flow meter that does not have any moving parts and is ideal for any liquid that is conductive. Magnetic flow meters are ideal for applications where low pressure drop and low maintenance are required.
The operation of a magnetic flow meter is based upon Faraday's Law of electromagnetic induction to detect the flow velocity of an electronically conducting fluid through a previously defined pipe diameter. Faraday’s Law states that the voltage induced across any conductor as it moves at right angles through a magnetic field is proportional to the velocity of that conductor.
Faraday's Formula: E is proportional to V x B x D where:
E = The voltage generated in a conductor
V = The velocity of the conductor
B = The magnetic field strength
D = The length of the conductor
To apply this principle to flow measurement with a magnetic flow meter, it is necessary first to state that the fluid being measured must be electrically conductive for the Faraday principle to apply. As applied to the design of magnetic flow meters, Faraday's Law indicates that signal voltage (E) is dependent on the average liquid velocity (V) the magnetic field strength (B) and the length of the conductor (D) (which in this instance is the distance between the electrodes).
SM series magnetic inductive flow meter
The SM magnetic inductive flow meter is designed to monitor all conductive media up to six gallons per minute. With its mechanically robust in-line design, the magmeter is intended for small diameter pipes. The meter features a 4-digit numeric display that indicates flow rate (gal/min or l/min), total volume (gallons or liters), and temperature (°F or °C). The setpoints are established through a simple pushbutton setup for switching, analog and
pulse outputs.
Applications include: Monitors all conductive media (>20µS/cm), 6.6 gpm or under.
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| | For technical information, click here:SM Series magnetic inductive flow meter |
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CALORIMETRIC FLOW TECHNOLOGY
Flow meter for metering applications
 | | | Rollover to enlarge | | Principle of operation
The technology behind the efector Metris meter is based on the calorimetric flow sensing principle. efector Metris incorporates two ceramic flow sensing elements that each contain a transistor. As one sensor element is heated, the second element is used as a reference. Power is then altered to the heaters to ensure a constant temperature difference (CTD) between two elements. The CTD method allows for greater sensitivity in air consumption, a faster response time, and a wide sensing range. Its acute sensitivity can detect extremely small leaks, yet at the same time, measure the air consumption of high-capacity compressed air systems.
efector Metris monitors compressed air and specialty gases such as Argon (Ar), Carbon dioxide (CO2), and Nitrogen (N2) to detect leakage areas and improve energy efficiencies. Compressed gases are considered one of the most expensive sources of energy consumption in a plant. By identifying leakage areas, efector Metris can optimize compressed gas usage, improve system performance, and reduce energy costs.
SD Series efector Metris
The compact sensor is fitted with an integrated pipe to ensure easy mounting and proper installation depth. The sensor’s 4-digit numeric display provides air and gas consumption readings and features microprocessor-based pushbutton setup. Three display options are available: cubic feet per minute, cubic feet per hour, and total consumed cubic feet. The 24 VDC unit provides switching, analog and pulse output options.
Applications include: metering gases and compressed air, argon, nitrogen and carbon dioxide.
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| | For technical information, click here:Flow meter for specialty gasesFlow meter for compressed air |
