Selecting the Right Measurement Tools: A Comprehensive Guide

At Automation Products Group, Inc. (APG), we offer a wide range of different pressure and level measurement tools for our customers to choose from. Each product line has its strengths and weaknesses. This blog post will focus on three different measurement tools: magnetostrictive float level transmitters, pressure sensors, and float switches.

Magnetostrictive Float Level Transmitters

Our magnetostrictive float level transmitters consist of a magnetic float that moves up and down a stem housing a wire waveguide. The float position can be measured because the waveguide is made of metal with ferromagnetic characteristics. This means the molecules in the metal waveguide align themselves with magnetic fields. A magnetostrictive float level transmitter uses two magnetic fields to align the molecules in different directions to create a detectable point on the wire waveguide. An electrical pulse travels down the waveguide and magnetizes it, aligning the molecules in one direction. When the pulse meets the competing magnetic field from the float, with molecules aligned in a different direction, a vibration travels back to the sensor housing at a known speed. This vibration is known as a strain pulse. By measuring the time delay between the initial electrical pulse and the strain pulse, the distance to the float can be determined with a high degree of accuracy.

These sensors are highly accurate in liquid level measurements, boasting excellence in vaporous liquids or in heavy foam where non-contact sensors may have difficulty. They excel in oil and water interface levels inside production tanks.

Limitations to magnetostrictive float level transmitters are stem length, as the length of the stem limits how deep the tank can be measured. Chemical compatibility can also be a concern. Material builds up in the bottom of the tank can affect where the bottom float rests, causing measurement accuracy issues.

 

Pressure Transmitters/Submersible Pressure Transmitters

Pressure transmitters use piezoresistive technology to accurately measure pressure. This is based off a small circuit called a Wheatstone bridge attached to the back of the diaphragm. As the diaphragm flexes from pressure, the resistance in the Wheatstone bridge changes relative to pressure, providing a basis of measurement.

Our submersible pressure transmitters work like other pressure transmitters, except they’re inside a water-tight housing, and they read in feet or inches of liquid adjusted to a specific gravity or other volumetric units of measure in addition to PSI. They are very compatible with most chemicals, and popular in the Oil and Gas Industries.

Our pressure transmitters are incredibly versatile. They’re often used in waste liquids where the exact chemical makeup is ill defined, and their low current draw makes them popular for battery powered applications. They’re frequently seen in wastewater lift stations.

They’re also designed to handle the following:

  • Dirt and fine dust
  • Water spray and washdowns
  • Outdoors and inclement weather
  • Hazardous locations
  • High vibration

Even pressure transmitters have their limitations. They don’t function well in viscous or sticky liquids. Using them in pressurized tanks is also not recommended, as the pressure in the tank will affect the reading the pressure transmitter gives. Pressure transmitters limitations are mainly due to the selection of the right pressure transmitter for each application. Selecting a non-submersible pressure transmitter to measure water in a tank will give poor results.

 

Float Switches

Float switches work much like a standard light switch: they open and close contacts to control where the signal current can pass through. They are either normally closed, meaning the current is flowing, or normally open, meaning the current is not flowing. The normal state is when the float switch is down, resting on its cable or float stop.

Our miniature float switches are an excellent choice for the food service industry, carrying NSF 169 certification for food-adjunct equipment and can handle temperatures up to 500˚ F. They are used in steamer reservoirs, commercial dishwashers and fryers, and ovens. Their small size allows them to nestle into tight spaces.

Limitations for our miniature float switches include placing them in environments that aren’t compatible with their stainless-steel design, or in sticky materials that will cause a buildup. Placing them in closed vessels with pressure over their ratings is also not recommended, and our miniature float switches should not be used to drive severe electrical loads or motors. Depending on the model, certain miniature float switches can only be installed vertically (FS-400 and FS-410) or horizontally (FS-500). Access to the inside of the tank is also required to mount a float switch.

 

Conclusion

Knowing how our level and pressure measurement products work is the first step in selecting the right product for your application. This overview should help you get started in your product selection.

If you have any further questions, our Sales Team is happy to answer your questions about our products. Please feel free to reach out to us today!

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