Level Detection Basics – Where to begin?

Initially I started to write this blog to compare photoelectric sensors to ultrasonic sensors for level detection. This came to mind after traveling around and visiting customers that had some very interesting applications. However, as I started to shed some light on this with photoelectrics, sorry for the pun but it was intended, I thought it might be better to begin with some application questions and considerations so that we have a better understanding of the advantages and disadvantages of solutions that are available. That being said I guess we will have to wait to hear about ultrasonic sensors until later…get it, another pun. Sorry.

Level detection can present a wide variety of challenges some easier to overcome than others. Some of the questions to consider include the following with some explanation for each:

  • What is the material of the container or vessel?
    • Metallic containers will typically require the sensor to look down to see the media. This application may be able to be solved with photoelectrics, ultrasonics, and linear transducers or capacitive (mounted in a tube and lowered into the media.
    • SmartLevelNon-metallic containers may provide the ability for the sensors look down to see the media with the same technologies mentioned above or by sensing through the walls of the container. Capacitive sensors can sense through the walls of a container up to 4mm thick with standard technology or up to 10mm thick using a hybrid capacitive technology offered by Balluff when detecting water based conductive materials. If the container is clear or translucent we have photoelectric sensors that can look through the side walls to detect the media. You can get more information in our white paper, SMARTLEVEL Technology Accurate point level detection.
  • What type of sensing is required? The short answer to this is level right? However, there are basically two different types of level detection. For more information on this refer to the Balluff Basics on Level Sensing – Discrete vs. Continuous.
    • Single point level or point level sensing. This is typically accomplished with a single sensor that allows for a discrete or an on-off signal when the level actuates the sensor. The sensor is mounted at the specific level to be monitored, for instance low-low, low, half full (the optimistic view), high, or high-high. These sensors are typically lower cost and easier to implement or integrate into the level controls.
    • Example of in-tank continuous level sensor
      Example of in-tank continuous level sensor

      Continuous or dynamic level detection. These sensors provide an analog or continuous output based on the level of the media. This level detection is used primarily in applications that require precise level or precision dispensing. The output signals are usually a voltage 0-10V or current output 4-20mA.  These sensors are typically higher cost and require more work in integrating them into system controls.  That being said, they also offer several advantages such as the ability to program in unlimited point levels and in the case of the current output the ability to determine if the sensor is malfunctioning or the wire is broken.

Because of the amount of information on level detection this will be the first in a series on this topic. In my next blog I will discuss invasive vs non-invasive mounting and some other topics. For more information visit www.balluff.us.

Quick field replacement for linear sensor electronics

Micropulse Transducers BTL 7 Rod-style with Rapid Replacement Module
Micropulse Transducers BTL 7
Rod-style with Rapid Replacement Module

When maintenance technicians replace linear position sensors (also known as probes or wands) from hydraulic cylinders, it can leave a terrible mess, waste hydraulic oils, and expose the individual to harmful hot fluids.  Also, the change out process can expose the hydraulic system to unwanted contaminants. After the sensor replacement has been completed, there can also be more work yet to do during the outage such as replacing fluids and air-bleeding cylinders.

Hydraulic linear position sensors with field-replaceable electronics/sensing elements eliminate these concerns.  Such sensors, so-called Rapid Replacement Module (RRM) sensors, allow the “guts” of the sensor to be replaced, while the stainless steel pressure tube remains in the cylinder.  The hydraulic seal is never compromised.  That means that during the replacement process there is no danger of oil spillage and no need for environmental containment procedures. There is also no need to bleed air from the hydraulic system and no danger of dirt or wood debris entering the open hydraulic port. Finally, there is no danger of repair personnel getting burned by hot oil.

The RRM is an option for Balluff’s BTL7 Z/B Rod Series used in applications for the lumber industry, plastic injection and blow molding, tire and rubber manufacturing, stamping presses, die casting, and all types of automated machinery where a continuous, absolute position signal is required.  Applications in industries such as Oil & Gas and Process Control are especially critical when it comes to downtime.  For these applications, this Rapid Replacement Module capability is especially advantageous.

You can learn more about linear position sensors with hazardous area approvals, by visting http://www.balluff.com/local/us/products/sensors/magnetostrictive-linear-position-sensors/

The video below shows a demonstration of the Rapid Replacement Module in action.

 

Improved Feedback for Valve Actuators

Here on SensorTech, we frequently talk about the need for high performance, rugged, reliable position feedback in modern industrial applications. A recent article in Valve Magazine, entitled “The Case for Magnetostrictive” illustrates how linear feedback transducers using non-contact magnetostrictive technology help to improve the performance and reliability of valve actuators used in the petrochemical industry.

It’s worth a read. See a variety of linear feedback transducers here.

Illustration of Magnetostrictive Linear Displacement Transducer (MLDT) inserted into a gun-drilled cylinder.
Illustration of Magnetostrictive Linear Displacement Transducer (MLDT) inserted into a gun-drilled cylinder.

GIZMOS

Plural of Giz-mo.  A noun.  Defined as a gadget, one whose name the speaker does not know.  Customers call us and ask for this or that “gizmo” all the time!  I think we should consider creating a product category simply called “GIZMOS”.

I like to call these things “Enablers” because these devices are very much helping hands that optimize the function of sensors.  A sensor of any brand and manufacturer performs only as well as it’s mounted, matching the fixture to the demands of the application at hand. But how often does this happen in a price-driven world?  They often end up in below-par mounting that fails with regularity, in both pristine environments as well as in hostile environments.  Some examples:

Here’s one example below. These inductive proximity sensors in plastic brackets, showing an exposed coil on one, with corroded mounts on the sensor caused by being beaten to death during parts loading and heat.

gizmo1      gizmo2

With a few “Gizmos” like an application-specific quick change mount, some care in gapping the sensor and guarding the cable/connector system, it could look much different. Check out the examples below.

gizmo4 gizmo5

Photoelectric sensors can suffer the same fate.  In this case, a plastic bodied photoelectric sensor, originally used to replace a fiber optic thru beam pair also suffered abuse. With a little extra beefy mounting, these photoelectric sensors can be expected to last a long time without failure.

gizmo6 gizmo7

There are literally hundreds of these mounting “ENABLERS”, off-the-shelf, cost-effective application specific mounts, guards, actuators and entire systems to help protect your sensor investment.  All categories of products have these “enabling” accessories for Magnetic Field (air cylinder), Inductive Proximity, Capacitive, Ultrasonic, Connectivity, Linear Transducer and Photoelectric product categories.