Can Linear Position Sensors Help Maintain Social Distancing?

Can Linear Position Sensors Help Maintain Social Distancing?
Can Linear Position Sensors Help Maintain Social Distancing?

There has been an increased focus on creating or improving automated manufacturing lines to comply with COVID-19 social distancing recommendations, while not compromising work safety and production stability. Linear Displacement Transducers (LDTs), often referred to as linear position sensors, play an important role in today's sophisticated, automated machinery.

In linear automation solutions, the host controller must provide accurate feedback of continuous position to improve productivity, efficiency, and personnel safety. Linear position sensors use magnetostrictive technology to provide precise and absolute non-contact position feedback down to 1-micron resolution.

How magnetostrictive technology works

Magnetostrictive technology is ideal for performing accurate and repeatable measurements of linear movement.  

Figure 1

In the head of a linear position sensor, circuitry generates a current pulse that is sent down a special magnetostrictive wire inside the sensor’s protective tube or extrusion (see Figure 1). On the outside of the tube, a moveable magnet is mounted, and connected to the moving part of the machinery or hydraulic cylinder. When the current pulse interacts with the moveable magnet, a torsional twist is generated that travels along the magnetostrictive wire at a fixed rate of speed.  The magnet’s position is precisely determined by measuring the time between the launch of the current pulse and the arrival of the torsional strain pulse. The result is accurate, noncontact position sensing with absolutely no wear on the sensing element.

Serial synchronous interface sensors

Potentiometers use an analog signal that can be fed into an analog input module or drive. However, analog signals are limited by the resolution of both the sensor and input module, they are also prone to degradation over long cable runs.

To overcome the shortcomings of traditional analog sensors, users often turn to Serial Synchronous Interface (SSI) sensors. SSI LDTs provide a serial-clocked output of binary or gray-code positional data with up to 1-micron resolution. The displacement value (position) is encoded into a 24-, 25- or 26-bit format.

A Serial Synchronization Interface is a closed-loop system. A clock-pulse train from a controller is used to shift out sensor data: One bit of position data is transmitted to the controller for each clock pulse received by the sensor. The absolute position data is updated continually by the sensor and converted by the shift register into serial information. SSI LDTs can interface seamlessly with the motion controllers or any programmable logic controller (PLC) that can talk SSI.

A disadvantage of SSI modules is that they typically cannot take in more than 2 axes per module. They also require a dedicated cable for each axis.

Can linear position sensors be connected to ethernet?

Gemco Linear Displacement Transducers are compatible with EtherNet/IP. Gemco network LDTs use magnetostrictive technology to provide absolute noncontact feedback and resolution to 1 micron. Network LTDs provide maximum flexibility for installation and ease of use in demanding, high-performance, networked industrial applications.

Ethernet compatibility is useful in instances when the desired resolution is not achievable using an analog device. Additionally, if EtherNet/IP devices are already a part of an automated workflow, a user can update analog machinery, and the continuous position, motion and velocity monitoring of equipment can be incorporated into the control system process via the network.

EtherNet/IP is the most developed, proven, and complete industrial Ethernet network solution available for manufacturing automation. EtherNet/IP systems require a single-point network connection for both configuration and control, thus simplifying installation and wiring.

Intelligent sensors

Position sensors can be field-configurable for output type, zero position, counting direction, position and velocity format, and resolution. Some sensors support wide-ranging power supplies (7VDC to 30VDC), so the same unit can be used in stationary or mobile applications.

The wide-ranging power supplies also help make the linear transducers backward compatible with older generations of transducers. Diagnostic LEDs help diagnose and aid in troubleshooting.  

Automatic gain, commonly referred to as AGC, helps compensate for the different style magnets that can be found in hydraulic cylinders. On power-up, most of these smart sensors can measure the strength of the magnet and automatically adjust their internal signal lengths to match that of the installed magnet. This is beneficial in hydraulic cylinder applications when the magnet installed in the cylinder might be a different brand (strength) than that of the sensor.

What is the best LDT for your application?

LDTs are typically available in two package styles (see Figure 2): the traditional rod-style package, suitable for installation into hydraulic cylinders, and the profile-style package that incorporates similar electronics but is housed in an aluminum extrusion housing for ease of mounting.

Figure 2

Magnetostrictive technology is the preferred method for receiving feedback from modern hydraulic cylinders (see Figure 3). The technology is absolute and can withstand the pressures and temperatures often associated with hydraulic cylinders. The sensors can handle operating pressures up to 5,000 psi and spikes to 10,000 psi, with response times in the milliseconds, and nothing to wear out.

Figure 3

The application or industry will dictate which linear position sensor style is best suited for you. Typical applications include:

• Steel mills.
• Hydraulic and pneumatic cylinders.
• Lumber mills.
• Hydropower.
• Pulp and paper.
• Tire and rubber.
• Stamping.
• Plastic injection molding.
• Or any application in which a machine is moving in a linear motion that requires feedback to automate the machine.

With the Covid-19 vaccines rolling out, the pandemic is beginning to lose strength. But the private, and industrial sectors have realized that maintaining safe distances will continue to lower infection rates of—not just COVID-19—but the common cold and flu; saving millions of working hours.

Learn more about linear position sensors and what AMETEK Factory Automation can do to help your manufacturing line to improved and stable automated workflow.

About The Author

Blake Cawley is a product manager with AMETEK Factory Automation. AMETEK Factory Automation is based in Peck, Mich. The company provides linear, rotary, level measurement technology, and cable and hose carriers.

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