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SM magmeters

Technology overview

Operating according to Faraday's law of induction, when a conductive medium flows through a magnetic field, a voltage proportional to the flow velocity / volumetric quantity is generated.

The voltage is tapped via electrodes and converted in the evaluation electronics to a usable control signal.

Applications

Cooling water

Flow rate of cooling water supply and return lines is critical in many applications, but highly accurate instruments can be expensive. What if you could accurately monitor flow rate in more of your supply and return lines?

Magnetic inductive technology provides precision measurement of water based media at an exceptional price in pipe sizes up to 2”.

Water treatment

What if you could use one instrument to monitor total volume of dosing chemicals as well as temperature of those chemicals?

The SM meter provides pulse and temperature outputs in one instrument. 

Unlock sensor potential with IO-Link

With IO-Link, process sensors have the ability to transmit multiple sensor values. Via IO-Link, the SM family can provide:

  • Flow rate
  • Totalized flow
  • Medium temperature
  • Remote parameterization

Media conductivity

FAQs

Q. If the conductivity of my liquid changes, will the SM magmeter be affected?

A. No. So long as the conductivity is at least 20 µS/cm, the magmeter will perform to specifications; higher or varying conductivity will not affect performance. Media with conductivity below the 20 µS/cm threshold produce low induction voltages, making it difficult or impossible to distinguish the difference between the signal voltages and noise voltages. 

Q. What is the impact of temperature, pressure and viscosity changes of my liquid?

A. Negligible when within our published specifications. Higher viscosity fluids will result in a larger pressure drop through the meter and a minor impact on accuracy. Medium temperature can be higher than specified when the ambient temperature is relatively low. 

Q. Can I use the SM in applications where the medium temperature is higher than the datasheet allows?

A. Yes, if the ambient temperature is lower than the maximum specified. For example, the SM is used in brewing applications for media temperature around 185 °F, but the ambient temperature is only around 70 °F. A general rule of thumb is for every degree the ambient temperature is lower than the maximum, the medium temperature can be one degree higher. This is valid for media temperature up to about 190 °F maximum.

Q. How do deposits on the measuring electrodes affect the meter?

A. Generally, magmeters are known to be low-maintenance. However, if the water quality is such that build-up of solids or other materials stick to the measuring electrodes, there will be a decrease in the signal until the build-up is removed. This can be done using a soft brush and an appropriate dilute cleaning solution. 

Q. What happens with bubbles in the medium?

A. Uncovered electrodes, due to air bubbles or because the pipe is not full will cause measuring errors. Larger magmeters (SM2xxx and SM9xxx) have built in empty pipe detection and can provide a stable “0” signal in these cases. 

Q. Must I do anything special to install the magmeter in a plastic pipe?

A. Because of the minimum measuring voltage required, stray grounding or noise current can cause errors. Make sure the meter is properly earth grounded. E40234 grounding clamp can be attached to the electrical connector and a ground wire can be run to earth ground.

Q. How do I calculate the accuracy of the SM meters?

A. Most of ifm’s flow meters use a two-part accuracy calculation, based on the measuring range (MW) and full range of the meter (MEW). For example, accuracy of the SM2001 (MEW = 160 gpm) is specified as:
                                    ± (0.8% MW + 0.5% MEW)
                                   For MW = 100 gpm, accuracy = ± (0.008*100 + 0.005*160) = 1.6 gpm

Q. What is the accuracy of the totalizer feature in the SM magmeters?

A. We do not specify the accuracy in our datasheet, but testing has shown accuracy in the 0.5% - 0.7% range.

Q. What is the difference between pulse output and frequency output?

A. The SM magmeters have a pulse output that is used for dosing or totalizing applications. A 24 VDC signal is sent every time a specified volume (e.g., 0.1 gallons, 1 ml, etc. entered as ImPS in the menu) flows through the meter regardless of the flow rate. The SM2xxx and SM9xxx meters also have frequency outputs, which provides a digital signal directly relatable to the flow rate. This digital signal can be further evaluated with counters, PLCs, etc. Frequency outputs are often used for mechanical flow meters like turbine meters. The rotational motion of the turbine, which turns according to the flow rate, is detected and converted into frequency signal.

Guided tours

The SM family has a pulse output for totalizing applications. Depending on the model, the pulse can be set as low as 1 milliliter. Here’s “how to” set up the meter for these applications.