Magmeters – Magnetic Flow Meters & Measurement For Conductive Liquids
Published 25 Sep 2016
T&D, Metering Specialists.
- By Chris Dodds : estimated reading time 7 minutes
What Is A Magmeter?
The term Magmeter is an amalgamation of the terms magnetic and meter.
The Magmeter is constructed from a non-magnetic flow tube, electrodes, liner and electromagnets to generate a magnetic field. These magnetic flow meters are used to typically measure fluid and flow rate which must be a conductive fluid.
As a rule, the minimum conductivity level of a fluid to measured with a Magmeter is 5 microS/cm.
Magnetic Inductive Flow Measurement
Magmeters are generally used because of their obstruction less design, linear signal output, high levels of accuracy and corrosion resistant wetted components. As there are no moving components throughout the flow meter there is nothing to cause an obstruction and therefore the pressure drop through the meter is virtually zero.
In addition to there being no pressure drop, the lack of moving parts also results in there being no wear on the magnetic flow meter throughout its lifetime.
The Magmeter contains an electromagnetic coil that produces the magnetic field that usually surrounds the outside of the non-magnetic pipe called the flow tube. An alternating current passes through the coils generating a magnetic field inside the flow tube.
The liquid being measured then passes through the flow tube perpendicular to the plane of the magnetic field that has been created. Typically a metal meter body is manufactured from 304 stainless steel that has strong non-magnetic properties allowing the magnetic field to pass through the meter body into the pipe area and therefore provide the flow signal.
The insulated liner that is installed in between the meter body and the electrodes is used to prevent the flow signal from being shorted-out as the voltage developed across the electrodes is generally a few millivolts in power.
Magnetic Flow Meter
Magmeters To Meet Every Requirement
SIKA 3 Types
There are 3 Magmeters available in the series of magnetic flow measurement instruments – Sika VMI, VMZ and VMM.
Each Magmeter has been manufactured for different application and developed specifically for individual applications.
HOW TO SELECT YOUR MAGMETER
- Is the fluid conductive or water based?
- Is the fluid or slurry abrasive?
- Do you require an integral display or remote display?
- Do you require an analogue output?
- What is the minimum and maximum flow rate for the flow meter?
- What is the minimum and maximum process pressure?
- What is the minimum and maximum process temperature?
- Is the fluid chemically compatible with the flow meter wetted parts?
- What is the size of the pipe?
- Is the pipe always full?
How To Maximise Your Magmeter
Magmeters are often used in applications where the media being monitored is harsh i.e sludge, sewage or other similar liquids. The magmeter is preferred due to its non-intrusive design, reliability, low maintenance and accuracy.
Magmeters have a larger range of flow than traditional meters however despite the rugged design and simplicity of use, there are still factors that can be incorporated to improve the performance of your electromagnetic flow meter.
- Ensure the flow media is above the minimum conductivity level – this measure ensures the electromotive force is able to drive the voltage and current into the signal electrodes.
- Make sure the meter tube is full at all times – by carrying out this check, the magmeter will not produce inaccurate or erratic readings and as most magmeters automatically assume the flow tube is full, they cannot detect a half empty pipe. Methods to ensure full liquid flow include:
- positive head pressure from pumps
- uphill grades
- vertical installation
- positioning the meter in the lowest point of a plumbing trap
- Ensure the magmeter is installed on a length of pipe with straight pipe before and after the meter.
- Make sure that provisions have been made proper connections and adequate grounding. Again, this will prevent the magmeter from giving inaccurate or erratic readings. The magmeter relies on a potential earth ground in order to operate.
- Know the metering application – by knowing what the magmeter application is, it is easier to select the correct converter orientation.
- Avoid any heavy vibration – Heavy external vibrations caused by a generator or diesel driven pump may damage the signal converter electronics. In order to mitigate the damage caused by vibration it is advisable to construct a concrete or steel support to absorb the vibrations.
- Avoid wide temperature variations – The magmeter electronics are sensitive and it is a good idea to cover the meter sensor to ensure accurate, consistent readings.
- Avoid any extreme heat from sources such as welding from going near the magmeter to ensure the liner and outer coatings do not become damaged. Any welding should be completed prior to installation of the flow sensor or alternatively compression and transition couplings can be used to avoid welding altogether.
SIKA VMI Magmeter
Due to its robust, strong metal housing and stable process connections, the Sika VMI Magmeter is particularly suited to applications within mechanical engineering and plant construction. The
design of the VMI means it is also suitable for use at high temperatures and high process pressures. In addition, the instrument can be supplied in three different sizes: VMI 07, VMI 10 and VMI 20.
The specifications of each flow meter varies:
VMI 07 Magmeter – Nominal diameter DN 7 Flow range 1…20 l/min
VMI 10 Magmeter – Nominal diameter DN 10 Flow range 2…40 l/min
VMI 20 Magmeter – Nominal diameter DN 20 Flow range 10…200 l/min
SIKA VMZ Magmeter
The Sika VMZ Magmeter is a magnetic inductive flow meter for electrically conductive liquids that has been designed specifically for original equipment manufacturer (OEM) applications. The VMZ
incorporates plastic components that are cost optimsed resulting in a lightweight design that it is available in six flow ranges.
The specifications of the VMZ magmeters are:
VMZ 030 Magnetic flow meter – Nominal diameter DN 3 Flow range 0.1…2 l/min
VMZ 081 Magnetic flow meter – Nominal diameter DN 8 Flow range 0.25…5 l/min
VMZ 082 Magnetic flow meter – Nominal diameter DN 8 Flow range 1…20 l/min
VMZ 153 Magnetic flow meter – Nominal diameter DN 15 Flow range 2.5…50 l/min
VMZ 204 Magnetic flow meter – Nominal diameter DN 20 Flow range 5…100 l/min
VMZ 205 Magnetic flow meter – Nominal diameter DN 20 Flow range 10…200 l/min
SIKA VMM Magmeter
The Sika VMM magnetic flow meters are suitable for use in harsh ambient conditions due to their robust design and construction. The steel construction is fully welded and therefore has great resistance to any potential interference.
The range of Sika VMM Magmeter nominal diameters cover fluid measurement requirements from medium flow rates right up to 10 m/s. The sensors are manufactured from high quality materials and provide solutions to numerous application possibilities.
The specifications of the nine variations of the VMM Magmeter are:
VMM32 Magnetic Inductive Flow Sensor – Nominal diameter DN 32 Flow range 0.25…10 m/s 0.72…29 m³/h
VMM40 Magnetic Inductive Flow Sensor – Nominal diameter DN 40 Flow range 0.25…10 m/s 1.15…45.2 m³/h
VMM50 Magnetic Inductive Flow Sensor – Nominal diameter DN 50 Flow range 0.25…10 m/s 1.8…70.7 m³/h
VMM65 Magnetic Inductive Flow Sensor – Nominal diameter DN 65 Flow range 0.25…10 m/s 3…119.5 m³/h
VMM80 Magnetic Inductive Flow Sensor – Nominal diameter DN 80 Flow range 0.25…10 m/s 4.5…181 m³/h
VMM100 Magnetic Inductive Flow Sensor – Nominal diameter DN 100 Flow range 0.25…10 m/s 7…282.7 m³/h
VMM125 Magnetic Inductive Flow Sensor – Nominal diameter DN 125 Flow range 0.25…10 m/s 11…441.8 m³/h
VMM150 Magnetic Inductive Flow Sensor – Nominal diameter DN 150 Flow range 0.25…10 m/s 16…636.2 m³/h
VMM200 Magnetic Inductive Flow Sensor – Nominal diameter DN 200 Flow range 0.25…10 m/s 28…1131 m³/h
Sika VMM Magmeters are available as either a compact or separate type installation – compact Magmeters are supplied as a complete unit whereas separate flow sensors are supplied in multiple sections.
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