Linear motor position sensor—What you need to know

What is a linear position sensor?

They are all around us – in our car suspension systems as we drive over speed bumps, in the trains we sit in as they move around curved tracks and in the ‘fly-by-wire’ aircraft that adjust their ailerons and elevators as they start to descend. They are in the factory machines that we work with every day to package and manufacture products, and in medical equipment that keeps us alive. What are these inconspicuous but crucial devices? They are linear position sensors which are helping to embed digital technologies in the next industrial revolution.

Linear position sensors and custom electronic circuitry

Linear position sensors measure the linear distance between an object and a point of reference, as well as speed and changes in position. They do this by converting linear displacement into an extra low voltage, in either an analog or digital signal. That electrical output is generated by exploiting different phenomena in nature such as magnetic fields, solar energy and electrical resistance. Excitation circuitry in the sensor creates a stimulus and signal conditioning circuitry then selects and amplifies the electrical response. Sensors then digitise the signal using an Analogue-to-Digital Converter (ADC), the digital result is then passed to a Central Processing Unit (CPU).

The Fourth Industrial Revolution

The Fourth Industrial Revolution or Industry 4.0 is well underway and adopting next generation linear position sensors that employ Application Specific Integrated Circuits (ASICs) to deliver the speed, accuracy and cost savings to industrial automation. Linear position sensors detect the location of machinery and equipment parts so they can be tracked and automated. They provide a digital signal via Ethernet connectivity to accurately report the target position in real-time with sufficient resolution. Sensor electronics are a key part of the evolution in automation, having direct influence on speed, accuracy and overall form factor.

What are the basic types of linear position sensor?

Linear position sensors consist primarily of two types: contact and non-contact, depending on whether they require physical contact to measure. Contact sensors tend to wear or degrade over time due to the constant friction for example of the wiper in a linear potentiometer measuring electrical resistance. In contrast, noncontact sensors use magnetic fields, solar energy and lasers to sense changes in position so they are less prone to wear and tear and can tolerate higher levels of vibration.

Products and reference designs of Linear motor position sensor

Design requirements

Linear motor position sensor systems often require:

  ●Magnetic or inductive sensors with high linearity and high bandwidth.

  ●High resolution, low latency and time synchronized linear position decoding.

  ●Low latency and fast serial interface to the segment controller with high EMC immunity.

DC/DC power supply

A supply voltage supervisor monitors the supply rails for overvoltage (OV) and undervoltage (UV) with high accuracy to ensure all voltage supply rails are within the system's specified operating voltage range. DC/DC power supply includes Buck converters (integrated switch)、Linear & low-dropout (LDO) regulators、Supervisor & reset ICs、Sequencers、eFuses & hot swap controllers、Load switches, the Corresponding products are TPS65251、TPS74301、TPS3847、LM3880、TPS25200、TPS22810

Position sensing

Multiple magnetic or inductive sensors are equally spaced to sense the movers position. The linear position of each mover is encoded into the output voltage of multiple sensors. Position sensing includes Multi-axis linear & angle position sensors、Inductive sensor AFEs、Linear Hall-effect sensors、Analog temperature sensors, the Corresponding products are TMAG3001、LDC1612、DRV5055、LMT89

Board-to-board interface

The Board-to-board interface connects to external devices or boards such as the linear motor segment controller board. It is typically a serial interface to reduce cabling. Board-to-board interface includes RS-485 & RS-422 transceivers、LVDS, M-LVDS & PECL ICs、Noninverting buffers & drivers、Inverting buffers & drivers, the Corresponding products are AM26LV31E、THVD1550、DS90LV011A、SN74LVC1G125

Digital processing

Digital processing decodes the position for each mover based on the digitized signals of the sense elements. It communicates with the segment controller for time synchronized position sampling. A high speed serial interface minimize latency. A typical approach to decode the position use the arc tangent method to eliminate variations with the movers magnetic field strength. It may leverage temp sensors to optimize the position accuracy over a wider temp range. Digital processing includes C2000 real-time microcontrollers, the Corresponding products are TMS320F28377D、TMS320F28375D

Sine/cosine analog front end

Converts the analog output signal from the linear position sense elements into the digital domain for linear position decoding of each mover. Typically requires simultaneous dual sampling ADCs with low latency. Sine/cosine analog front end includes Precision ADCs、Fully differential amplifiers、High-speed op amps (GBW ≥ 50 MHz)、Comparators、Series voltage references, the Corresponding products are ADS1220、THS4551、TLV2365、TLV3202、REF20-Q1

Temperature sense interface

Converts the output voltage from the temp sensors or thermistor to digital. Temperature sense interface includes Precision ADCs, the Corresponding products are ADS1220、ADS8354

How can Live Electronics support manufacturers with linear position sensors?

Here at Live Electronics we are continually looking for the best products at the best price to help with modern technologies such as linear position sensors. Our linear position sensors from ZF use Hall Effect technology which allows the sensors to be non-contact resulting in highly precise measurements and an exceptionally long mechanical life.