Glossary & FAQs

Abrasive materials

Abrasive materials are a frequent cause of wear and tear on moveable parts in sensors. These abrasive materials include, for example:

• Quartz dust

• Metal oxide

• Ceramic dust

POSIWIRE® Position Sensors

Abrasive materials can cause unexpectedly high levels of wear and tear on the sliding components of the cable, cable outlet and cable drum. We recommend a prior precise check of your area of use, so that the right WS Position Sensor can be used for your special requirements.

POSIMAG® Position Sensors

On POSIMAG® Position Sensors, abrasive materials can cause wear and tear between the head plate and cover strip when the distance between the head and the strip is small.

POSICHRON® Position Sensors

On POSICHRON® systems with guided position magnet, abrasive materials can cause severe wear and tear of the guiding elements. We therefore recommend, wherever possible, that you use non-guided position magnets. On unguided systems, the completely wear-free POSICHRON® principle is used.

LVDT

With LVDT sensors, high levels of wear and tear must be expected in the presence of abrasive materials.

 

Acceleration, maximum

POSIMAG® Position Sensors

POSIMAG® Position Sensors are not limited by a maximum acceleration, but by a limited travel speed.
See Travel speed, POSIMAG®.

POSICHRON® Position Sensors

For the POSICHRON® position magnets, there is essentially no limit for the acceleration or travel speed.

WS Position Sensors

With WS Position Sensors, close attention must be paid to the model-specific maximum acceleration of the measuring cable, since otherwise the sensor will be destroyed. The biggest risk arises in the event of a sudden stop or extremely high acceleration in the direction of feed. A fast stop in the direction of feed doesn't generally cause a problem. Oscillations should be avoided, however.

 

Accuracy

WS-Position Sensors

The accuracy of WS sensors is primarily described as its linearity. In the sensor's nomenclature L10 represents a linearity of +/- 0.10% of the full scale measurement range of the particular sensor.

For WS position sensors, the accuracy depends upon the sensor's mechanical system and the tolerance of the angular sensing element. The concentricity of the cable drum, the eccentricity of the shafts, the tolerance of the diameter and flattening of the measuring cable and the static and dynamic stretching of the measuring cable all have varying influences in the sensor's accuracy. Thicker measuring cables tend to exhibit more cable flattening and lead to greater measurement errors. The proper coordination of the required cable tensile strength and cable construction minimizes the measurement errors associated with the cable. The range of linearity for WS sensors with potentiometers is from 0.35% to 0.01%, although the resolution is essentially infinite. This high resolution is only achieved with special hybrid ASM potentiometers. Only hybrid potentiometer are designed and constructed according to ASM specifications are used in ASM WS cable actuated position sensors.

POSICHRON® Position Sensors

The accuracy of the POSICHRON® family of position sensors is one of the most accurate technologies among contact-free measurement systems. Depending on the measurement range and style, the linearity range is between 0.2% to 0.01% is possible. These linearity values can be further enhanced through the use of external linearization programs. The repeatability (ability to return to the identical position from the identical starting point) of POSICHRON® sensors is rated up to 0.001% of full scale.

POSIMAG® Position Sensors

The linearity of the POSIMAG® position sensors arises through the accuracy of magnetization of the magnetic scale. Typical linearity values are about 30 µm/m.

 

Application consulting

The more detailed we are able to analyse your specific application in, the better we can advise you and recommend the most suitable measuring principle and best model for your needs. For this reason, we have developed a special projection plan which enables you to describe your application to us and allows us to offer you the best possible advice. You will find this questionnaire at the end of each position sensor catalogue.

 

Cable diameter

The diameter of the measuring cable depends on the sensor type and can be between 0.3 mm and 0.8 mm. With some sensors, larger cable diameters are available on request, however a larger cable sag needs to be taken into account in these cases. Due to the fact, that the mass increase of a thicker measuring cable takes place directly on the outer circumference of the drum, i.e. at the most unfavourable spot with the most negative effect on the dynamism, a larger cable diameter also has a deleterious effect on the increase in mass inertia of the moving elements.

 

Cable extension transducer (CET)

The term "cable extension transducer (CET)" refers to Position Sensors based on the cable activated principle. For this Position sensor principle, there are various different and in some cases confusing designations in the English-speaking world: string potentiometer, draw wire sensor, draw wire transducer, yo-yo sensor, pull wire sensor, wire transducer, cable extension transducer (CET).

In the German-speaking world, the following terms are used: Wegsensor nach Messseilprinzip, Seilzugsensor, Fadenpotentiometer, Zugdrahtsensor, Seilgeber, Seilzugaufnehmer, Seilzug-Weg-/Winkel-Wandler oder Schnürli-Geber.

In the early 1980s, K. M. Steinich, the founder and managing director of ASM GmbH, coined the term "WS Position Sensors“ for a new generation of industry-compatible position sensors based on the position cable principle. "WS" stands for "Wegseil" in the German-speaking world and "Wire Sensor" in the English-speaking world.

For a description of the measuring principle, see WS Position Sensors, measuring principle.

 

Clearance

POSIMAG®: The Sensing Head / Magnetic Tape Clearance


The clearance between the sensing head and the magnetic tape is dependant upon the magnetic period of the magnetic tape. The clearance distances are as follows:

• 2 mm Magnetic Period System typical clearance distance 0.1 to 1 mm

• 5 mm Magnetic Period System typical clearance distance 0.1 to 2 mm

Please refer to the individual data sheets for the exact values.

 

Controller PLC Connection

The connection of a POSIMAG® system to a controller is uncomplicated when the PLC is configured to accept incremental encoder inputs. The indicated resolution is achieved by the two-channel quadrature detection circuit inside of the PLC which edges of the A/B signals. The PLC or counter must be able to handle the maximum output pulse frequency of the sensor. If there is a mis-match, the controller may skip some pulses.

 

Corrosion

In normal industrial environments, corrosion is not generally a problem. Extreme corrosion can, however, occur in environments where aggressive chemicals are used, e.g in electroplating plants, galvanising shops or in systems where sulphur hydride is generated, or where brine is present.

Where applications involve corrosive media, we recommend that you discuss your requirements with ASM. Our experienced product team would be happy to help.

 

Delivery times

At ASM, many standard sensors are available from our warehouse. Special versions can generally be produced in a short period.

 

Draw string potentiometer

The term "draw string potentiometer" refers to Position Sensors based on the cable actuated principle. For this Position sensor principle, there are various different names and in some cases confusing designations in the English-speaking world: cable actuated sensor, string pot, string potentiometer, draw wire sensor, draw wire transducer, yo-yo sensor, pull wire sensor, wire transducer, cable extension transducer (CET).

In the German-speaking world, the following terms are used: Wegsensor nach Messseilprinzip, Seilzugsensor, Fadenpotentiometer, Zugdrahtsensor, Seilgeber, Seilzugaufnehmer, Seilzug-Weg-/Winkel-Wandler oder Schnürli-Geber.

In the early 1980s, K. M. Steinich, the founder and managing director of ASM GmbH, coined the term "WS Position Sensors“ for a new generation of industry-compatible position sensors based on the position cable principle. "WS" stands for "Wegseil" in the German-speaking world and "Wire Sensor" in the English-speaking world.

For a description of the measuring principle, see WS Position Sensors, measuring principle.

 

Encoder, absolute

An absolute encoder relays additional information so that the exact position is always known. During a power outage or short term electromagnetic interference, incorrect position information may be transmitted. After the power is restored or interference is resolved, the exact position data is provided. This performance is very important for many positioning systems. Additional failure codes are used to notify and correct errors. Although they are more expensive, absolute encoders are increasingly chosen over incremental encoders in WS position sensors.

 

IP-Code (International Protection Code)

The IP Code (International Protection Code), in accordance with DIN EN 60529, comprises two digits and determines the following:

1. The protection of individuals against access to dangerous parts within the casing

2. The protection of the operating equipment within the casing against the intrusion of solid foreign bodies

3. The protection of the operating equipment within the casing against harmful effects caused by the penetration of water

Die erste Kennziffer des IP-Codes steht für den Berührungs- und Fremdkörperschutz. Die zweite Ziffer steht für den Schutz gegen das Eindringen von Flüssigkeiten.

The first digit in the IP code represents the protection against contact and foreign bodies. The second digit represents the protection against the penetration of liquids.

All the designs of WS Position Sensors are tested in accordance with DIN EN 60529. The levels of protection attained are shown in the data sheet. The IP code does not apply for the cable drum casing. For POSIMAG® and POSICHRON® Position Sensors the values are demonstrated likewise in the data sheet.

 

Installation position

POSICHRON® Position Sensors

POSICHRON® Position Sensors can be installed in any desired installation position.

POSIMAG® Position Sensors

The installation position for POSIMAG® Position Sensors can also be freely selected.

WS Position Sensors

ASM WS sensors are suitable for horizontal and vertical installation. Over large travel distances of ~20 m ++, the cable sag must be borne in mind with horizontal measuring cables.

 

Life expectancy

POSICHRON® Position Sensors

By design, POSICHRON® position sensors from ASM are contact-free and wear-free. Since the components are not subject to typical aging that are found with contact type measuring systems, ASM POSICHRON® position sensors can be used for extended periods without calibration.

POSIMAG® Position Sensors

POSIMAG® Position sensors with its contact-free position magnetic tape and non-contact sensor head are wear-free by design. In the applications that use the guided sensor head system, some wear can be expected depending on the environmental conditions.

WS-Position Sensors

The life expectancy of the various models in WS position sensor family depends upon the operating conditions. Depending on the series and environmental conditions, several parameters greatly influence the life of the sensor and need to be addressed for each individual application. The life expectancy can be between multiple million measurement cycles to in very extreme case only a few cycles. Under normal industrial operating conditions, > 10 million position measurements can be achieved. However, the presence of abrasive dusts, corrosive media and very high measurement frequencies can significantly reduce the life expectancy. Please consult our application engineers to discuss your application in detail and find out ways to mitigate a reduction in the sensors' life expectancy.

Besprechen Sie deshalb Ihre Applikation mit unseren Produktingenieuren, um eine Abschätzung der zu erwartenden Lebensdauer des POSIWIRE®-Positionssensors für Ihren speziellen Einsatzfall machen zu können.

 

Low Ambient Temperatures

WS Position Sensors

The use of WS Position Sensors in ambient temperatures below 0° C may require preventative measures to protect internal condensation from freezing the sensing cable onto the cable drum. Over time, ice can also accumulate on the sensing cable and damage the sensor upon cable retraction. If the proper steps are taken, the sensors can continue to operate under these conditions. For example, a heater can be installed inside of the sensor, a external pulley and/or cable brush can be added to control icing. Please contact our application engineers for further details.

POSICHRON® Position Sensors

For POSICHRON® sensors with unguided magnets, low ambient temperatures do not have a negative impact on the sensor's functions.

POSIMAG® Position Sensors

For POSIMAG®, the accumulation of ice on the magnetic material is possible provided that the proper air gap tolerance is maintained.

 

Magnetic encoder

Along with optical encoders, magnetic encoders are also widely used. In general, optical encoders have higher resolution capabilities. However, magnetic encoders have been preferred in specific applications for their robustness.

 

Magnetic scale, the influence oft external magnetic

POSIMAG® Position Sensors

For POSIMAG® position sensors, external magnetic fields (AC or DC) over 50 milliTesla need to be avoided. With external fields greater than 200 milliTesla, the magnetization of the magnetic scale can be irreversibly destroyed.

 

Magnetostriction

The magnetostrictive effect (also known as the Joule Effect) on metallic wire or rod creates a change in length or volume of the wire or rod in the presence of a magnetic field. Ferromagnetic metals can have negative or positive magnetostrictive properties, for example they can shrink or stretch which in turn decreases or increases its volume. This effect is used in POSICHRON® position sensors.

 

Measurement accuracy

WS position sensors

The measurement accuracy of WS sensors is primarily described as its linearity. In the sensor's nomenclature L10 represents a linearity of +/- 0.10% of the full scale measurement range of the particular sensor.

For WS position sensors, the accuracy depends upon the sensor's mechanical system and the tolerance of the angular sensing element. The concentricity of the cable drum, the eccentricity of the shafts, the tolerance of the diameter and flattening of the measuring cable and the static and dynamic stretching of the measuring cable all have varying influences in the sensor's accuracy. Thicker measuring cables tend to exhibit more cable flattening and lead to greater measurement errors. The proper coordination of the required cable tensile strength and cable construction minimizes the measurement errors associated with the cable. The range of linearity for WS sensors with potentiometers is from 0.35% to 0.01%, although the resolution is essentially infinite. This high resolution is only achieved with special hybrid ASM potentiometers. Only hybrid potentiometer are designed and constructed according to ASM specifications are used in ASM WS cable actuated position sensors.

POSICHRON® Positions sensors

The accuracy of the POSICHRON® family of position sensors is one of the most accurate technologies among contact-free measurement systems. Depending on the measurement range and style, the linearity range is between 0.2% to 0.01% is possible. These linearity values can be further enhanced through the use of external linearization programs. The repeatability (ability to return to the identical position from the identical starting point) of POSICHRON® sensors is rated up to 0.001% of full scale.

POSIMAG® Positions sensors

The linearity of the POSIMAG® position sensors arises through the accuracy of magnetization of the magnetic scale. Typical linearity values are about 30 µm/m.

 

Measurement dynamics

The measurement dynamics of position measuring system involves the possible delay in the reading of a position relative to the actual position.

WS Position Sensors

The design of WS position sensors have been optimized for measuring dynamic systems. The support masses have been minimized while the recoil springs have been optimized for each frame size. The information contained in the data sheets for the WS position sensor series is based upon the maximum allowable accelerations for real-time data.

A significant reduction in the life of the sensor is always a consequence when the application exceeds the stated maximum dynamic conditions.

 

Measuring cable, diameter

The diameter of the measuring cable depends on the sensor type and can be between 0.3 mm and 0.8 mm. With some sensors, larger cable diameters are available on request, however a larger cable sag needs to be taken into account in these cases. Due to the fact, that the mass increase of a thicker measuring cable takes place directly on the outer circumference of the drum, i.e. at the most unfavourable spot with the most negative effect on the dynamism, a larger cable diameter also has a deleterious effect on the increase in mass inertia of the moving elements.

 

Measuring cable, wear and tear

The measuring cables used by ASM in its WS Position Sensors are designed for many millions of interactions. Exceptional wear and tear of the measuring cable of a WS Position Sensor can be caused by a number of factors:

• Direct mechanical damage (e.g. wear and tear on the base, bending of the measuring cable during installation or operation)

• Deposition of abrasive materials on the measuring cable

• Deposition of adhesive or glue-like materials on the measuring cable

• Extremely high / low temperatures

• A skewed feed of the measuring cable with sawing into the cable outlet

• Snapping of the measuring cable with unchecked winding and collision of the cable stop element on the cable outlet

• Deflection of the measuring cable over one or more deflection reels with too small a diameter

• Multiple deflection in opposite direction

• The measuring cable is fed through an opening with too small a diameter, causing it to rub against it and wear

• Material fatigue of the measuring cable caused by attainment of the bending fatigue strength

 

Measuring lengths, maximum

POSICHRON® Position Sensors

• up to 6 m

POSIMAG® Position Sensors

• up to 30 m

WS Position Sensors

• up to 60 m

 

Mechantronic

Mechantronic is the multi-discipline combination of mechanical and electronic systems in one assembly.

 

Optical encoder

Along with solutions using potentiometers, various types of encoders are being used. Encoders are separated into two groups: absolute encoders and incremental encoders.

Most linear and rotary encoders operate with either a contact-free optical or magnetic sensing technology. The line segments (for incremental encoders) or code pattern (for absolute encoders) are systematically placed onto sheets of glass, metal or plastic which are read into a digital signal by a contact-free LED / photodiode (for optical encoders) or magnetic sensing element (for magnetic encoders). Through the use of optical masks in specific orientations, additional output signal types can be produced such as reference signals.

Optical encoders have the following advantages:

• higher resolution

• availability of many different output protocol types

 

Output types

POSICHRON® Position Sensors

For POSICHRON® sensors, the following start-stop output types are available

• 0-10 V

• 4-20 mA

• and Profibus

POSIMAG® Position Sensors

POSIMAG® sensors are available with pulse output A/B x 4.

POSIWIRE® Position Sensors

For WS Position Sensors, the following output types are available:

• R1R

• 0-10 V

• 4-20 mA

• SSI

• all common bus systems

 

POSICHRON® Position Sensors, measuring principle

The principle of POSICHRON® Position Sensors is based on the time of flight principle of a mechanical-elastic density wave in a metallic solid, the waveguide, which simultaneously exhibits magnetostrictive and magneto-elastic properties.

Mechanical-elastic density waves are propagated in solids as a function of the density of that solid, and of the elasticity module or modulus of rigidity, at a very constant speed. Mechanical-elastic density waves are density waves in the crystalline spectrum. No material transport or movement takes place. Instead, energy is transported.

The propagation speed depends, in addition to the density, on the wave mode, i.e. whether the wave being propagated through the solid is longitudinal or torsional. The propagation speed is between 2500 and 5000 m/s, depending on the wave mode and the material used for the waveguide. Because the frequency of the propagation speed is outside the audible range of the human ear, many publications often speak of ultrasonic waves. However, to ensure a physically correct representation, we always talk of mechanical-elastic density waves in the context of Hooke's law.

As a medium for continuation of mechanical-elastic density waves for use in position sensors based on the time of flight principle, virtually any homogenous solid is suitable whose modulus of elasticity remains constant over a wide temperature range. Metals, which also demonstrate magnetostrictive and / or magnetoelastic properties have proven to be particularly suitable and advantageous for position sensors based on the time of flight principle.

 

POSIMAG® Position Sensors, measuring principle

With the POSIMAG® length measuring system, a magneto-resistive sensor samples the magnetic fields on a magnetic standard without making contact and thus remains free from wear and tear. The sensor's sine-cosine signals, which are displaced by 90 °, are instantly converted by the integrated interpolation electronics, together with the reference signal, into RS422-compatible signals and these are then output. Resolutions down to 5 µm are possible. As a fast transducer with no time delay, POSIMAG® is particularly suitable when used in conjunction with servo controls.

The magnetic standard is designed a a flexible steel strip with an applied magnetic layer. This magnetic layer is magnetised at regular intervals and fixed firmly in place with a carrier strip. To protect against mechanical influences, the magnetic strip can be covered with a non-magnetic steel strip.

To determine position, the scanning head is guided along the standard strip, at a short distance away. The magnetic field and thus the path information is therefore recorded without any contact being made. The distance between the standard strip and the scanning head should be between 0.1 mm and 0.5 mm for sensors with a 1 mm pole pitch. For sensors with a 5 mm pole pitch, the distance should be up to 2 mm.

The magnetic standard can be installed easily. It is installed by sticking the magnetic strip to the prepared base (e.g. machine bed) using an adhesive film applied at the factory.

 

POSIMAG® pulse output

The POSIMAG® output consists of two square waveform outputs (A/B), where the B signal is shifted by 90° with respect to the A signal. The two A/B signal can be fed into a quadrature detection circuit to increase the encoder resolution by a factor of 4X by counting the four edges per one pulse cycle.

 

Resolution

POSIMAG® Position Sensors

For POSIMAG® position sensors, the indicated resolution is achieved by the quadrature detection inside of the controller (PLC). The published POSIMAG® resolutions are after the quadrature signal processing of the A/B channels in the PLC. WS Position Sensors: The resolutions of a WS position sensor depends on the individual sensing element type. For analog versions, ASM uses a hybrid potentiometer with a essentially infinite resolution. For the WS sensors with digital absolute or incremental encoders as the sensing element, the resolution is up to 25 pulses per mm. Through the use of an external quadrature circuit, the resolution increases by a factor of four. However, this increased resolution can too high pulse frequencies that exceed the rating of the PLC. In these cases with very high pulse frequencies, an encoder with a sinusoid output signal can be used.

 

Sensors

A "sensor" is a product which can measure physical parameters such as pressure, temperature, travel, angle, position, etc.

 

String potentiometer

The term "string potentiometer" refers to Position Sensors based on the cable activated principle. For this Position sensor principle, there are various different and in some cases confusing designations in the English-speaking world: string potentiometer, draw wire sensor, draw wire transducer, yo-yo sensor, pull wire sensor, wire transducer, cable extension transducer (CET).

In the German-speaking world, the following terms are used: Wegsensor nach Messseilprinzip, Seilzugsensor, Fadenpotentiometer, Zugdrahtsensor, Seilgeber, Seilzugaufnehmer, Seilzug-Weg-/Winkel-Wandler oder Schnürli-Geber.

In the early 1980s, K. M. Steinich, the founder and managing director of ASM GmbH, coined the term "WS Position Sensors“ for a new generation of industry-compatible position sensors based on the position cable principle. "WS" stands for "Wegseil" in the German-speaking world and "Wire Sensor" in the English-speaking world.

For a description of the measuring principle, see WS Position Sensors, measuring principle.

 

Transducer

A "transducer" is a product which can measure physical parameters such as pressure, temperature, travel, angle, position, etc. However, the term "sensors" is todays established international term.

 

WS Position Sensors, measuring principle

WS Position Sensors from ASM essentially comprise the following components:

•  A specially-produced and precise, calibrated measuring cable
•  A precision-made measuring cable drum
•  A measuring axis and clock-spring motor


An angle sensor element (precision potentiometer, incremental or absolute encoder) linked to a wave, together with cable stop elements for anchoring and fixing the measuring cable are housed, together with the other mechanical components and sensor electronics, in a casing, where they are protected against external influences. The precision measuring cable is wound in one layer tightly round the drum. The lightweight precision drum is driven over the specified number of turns by the clock-spring motor against the direction of extraction and winds the measuring cable with a constant return force. Because of the clock-spring motor, the measuring cable is always under a relatively constant return tension. The return force of the spring is selected so that the system is balanced by the mass inertia, friction and other incidental dynamic forces, and the measuring cable is always kept taut under the specified conditions. The limits for the acceleration values specified for the relevant WS positional sensor must not be exceeded, since otherwise the cable will go slack. Precise winding of the cable is then no longer guaranteed, and the sensor will eventually fail. Thanks to the winding of the measuring cable on the drum circumference, the linear movement of the measuring cable, which is linked with the moving measuring object, is converted into an angular movement. This angular movement is now converted by suitable sensor elements into an electrical output signal, which is proportional to the linear movement of the measuring object.

 

Wire transducer

The term "wire transducer" refers to Position Sensors based on the cable activated principle. For this Position sensor principle, there are various different and in some cases confusing designations in the English-speaking world: string potentiometer, draw wire sensor, draw wire transducer, yo-yo sensor, pull wire sensor, wire transducer, cable extension transducer (CET).

In the German-speaking world, the following terms are used: Wegsensor nach Messseilprinzip, Seilzugsensor, Fadenpotentiometer, Zugdrahtsensor, Seilgeber, Seilzugaufnehmer, Seilzug-Weg-/Winkel-Wandler oder Schnürli-Geber.

In the early 1980s, K. M. Steinich, the founder and managing director of ASM GmbH, coined the term "WS Position Sensors“ for a new generation of industry-compatible position sensors based on the position cable principle. "WS" stands for "Wegseil" in the German-speaking world and "Wire Sensor" in the English-speaking world.

For a description of the measuring principle, see WS Position Sensors, measuring principle.

 

Yo-yo Sensor

The term "Yo-yo sensor" refers to Position Sensors based on the cable activated principle. For this Position sensor principle, there are various different and in some cases confusing designations in the English-speaking world: string potentiometer, draw wire sensor, draw wire transducer, yo-yo sensor, pull wire sensor, wire transducer, cable extension transducer (CET).

In the German-speaking world, the following terms are used: Wegsensor nach Messseilprinzip, Seilzugsensor, Fadenpotentiometer, Zugdrahtsensor, Seilgeber, Seilzugaufnehmer, Seilzug-Weg-/Winkel-Wandler oder Schnürli-Geber.

In the early 1980s, K. M. Steinich, the founder and managing director of ASM GmbH, coined the term "WS Position Sensors“ for a new generation of industry-compatible position sensors based on the position cable principle. "WS" stands for "Wegseil" in the German-speaking world and "Wire Sensor" in the English-speaking world.

For a description of the measuring principle, see WS Position Sensors, measuring principle.