Continuous and Exacting Measurements Deliver New Levels of Quality Control

Quality control has always been a challenge. Going back centuries, the human eye was the only form of quality verification. Hundreds of years ago metal tools like calipers were introduced to allow for higher repeatability compared to the human eye. This method is very cumbersome and is only an approximation based off a sample of the production, potentially allowing faulty products to be used or shipped to the customer.

What is the best solution by today’s standards? By scanning the product at all times! Using continuous measurements reduces or even eliminates the production of faulty products and allows for consistent and repeatable production. This used to be an impossible task for small products, but with the invention of the laser and CMOS(Complementary Metal Oxide Semiconductor) imaging sensors, extremely small measurements can be achieved. How small? In an industrial environment, measuring 0.3 mm components with a resolution of 10 micrometers is absolutely attainable. Using special optics to spread the beam across a window will allow for 105 mm of measuring range and up to 2 meters distance between the transmitter (laser spread light) and receiver (CMOS sensor).

Traditionally these sensor systems have one or two analog outputs and have to be scaled in the control system to be usable. These values are repeatable and accurate once scaled but there has to be a better way. IO-Link to the rescue!

IO-Link brings an enormous amount of information and flexibility to configuration. Using IO-Link will also reduce the amount of wiring and analog input cards/hubs required. The serial communications of IO-Link also reduce overall costs thanks to its use of standard cables, as opposed to shielded cables. This allows for 20 meter runs over a standard double ended M12 cables without information loss or noise injection. Another benefit to going with IO-Link is the drastic increase in bits of resolution. Analog input cards and analog input hubs tend to provide between 10-16 bits of resolution, whereas IO-Link has the ability to pass two measurements via process data in the form of dual 32 bit resolution arrays as well as more information about the status of the sensors.

With IO-Link, you also gain the ability to use system commands like restarting the device, factory reset, signal normalization, reset maintenance interval, and device discovery. With this level of technology and resolution, quality control can be taken to down to the finest details.

Back to the Basics: Measuring

In the last post about the Basics of Automation, we discussed how objects can be detected, collected and positioned with the help of sensors. Now, let’s take a closer look at how non-contact measurement—both linear and rotary—works to measure distance, travel, angle, and pressure.

Measuring travel, distance, position, angle and pressure are common tasks in automation. The measuring principles used are as varied as the different tasks.

Sensor Technologies

  • Magnetostrictive enables simultaneous measurement of multiple positions and can be used in challenging environments.
  • Magnet coded enables the highest accuracy and real-time measurement.
  • Inductive is used for integration in extremely tight spaces and is suitable for short distances.
  • Photoelectric features flexible range and is unaffected by the color or surface properties of the target object.

Different Sensors for Different Applications

Distance measurement

Janni1Disc brakes are used at various locations
in wind power plants. With their durability and precise measurement, inductive distance sensors monitor these brake discs continuously and provide a timely warning if the brake linings need to be changed.

In winding and unwinding equipment, a photoelectric sensor continuously measures the increasing or decreasing roll diameter. This means the rolls can be changed with minimal stoppages.

Linear position measurement

Janni4Workpieces are precisely positioned on the slide of a linear axis. This allows minimal loss of production time while ensuring quality. Magnetic encoders installed along the linear axis report the actual slide position to the controller (PLC) continuously and in real time — even when the slide is moving at a speed of up to 10 m/s.

In a machine tool the clamping state of a spindle must be continuously monitored during machining. This improves results on the workpiece and increases the reliability of the overall system. Inductive positioning systems provide continuous feedback to the controller: whether the spindle is unclamped, clamped with a tool or clamped without a tool.

Rotational position measurement

Janni5Workpieces such as a metal plate are printed, engraved or cut on a cut/print machine. This demands special accuracy in positioning it on the machine. Magnetic encoders on both rotating axes of the machine measure the position of the workpiece and ensure an even feed rate.

In a parabolic trough system,
sunlight is concentrated on parabolic troughs using parabolic mirrors allowing the heat energy to be stored. To achieve the optimal energy efficiency, the position of the parabolic mirror must be guided to match the sun’s path. Inclination sensors report the actual position of the parabolic mirror to the controller, which then adjusts as needed.

Pressure and Level Measurement

Janni7Consistently high surface quality of the machined workpiece must be ensured in a machine tool. This requires continuous monitoring of the coolant feed system pressure. Pressure sensors can reliably monitor the pressure and shut down the machine within a few milliseconds when the defined pressure range is violated.

Janni8In many tanks and vats, the fill height of the liquid must be continually measured. This is accomplished using ultrasonic sensors, which note levels regardless of color, transparency or surface composition of the medium. These sensors detect objects made of virtually any material (even sound-absorbing) including liquids, granulates and powders.

Stay tuned for future posts that will cover the essentials of automation. To learn more about the Basics of Automation in the meantime, visit