Unternehmen
Zettlex ist eine Sensorfirma.Unsere Sensoren messen selbst unter härtesten Bedingungen akkurat und zuverlässig Position oder Geschwindigkeit - daher kommt unser Motto - 'Präzision im Extremen'. Wir
- entwerfen und produzieren Sensoren
- liefern Sensorkomponenten und integrierte Schaltkreise
- entwickeln Sensoren nach Kundenanforderungen.
Einzigartige Technologie und eine laminare, bedruckte Konstruktion ermöglichen Sensoren ohne Kontakte, ohne Lager, ohne empfindliche Teile, ohne Wartung, ohne Ärger.....einfach akkurate Messungen - den ganzen Tag - jeden Tag.
Wir verkaufen an Originalausrüster und Systemintegratoren in vielen verschiedenen Bereichen. Die Anwendungen umfassen Positionsmessung, Bedienerschnittstellen und Servo- und Motorsteuerungen. Ungefähr die Hälfte unseres Geschäfts tätigen wir in Sicherheits- oder in sicherheitskritischen Anwendungen.
Die Ingenieure von Zetlex zählen zu den weltweit führenden Experten in diesem Bereich.
Zettlex ist für die Herstellung von elektromagnetischen Sensoren einschließlich Sensoren für eigensichere (ATEX) Umgebungen nach ISO 9001 und BS EN 13980 zertifiziert.
Zettlex sensors measure position or speed. They use a resonant inductive technique with printed circuit boards (PCBs) as their main components. This enables a non-contact measurement technique offering highly accurate and stable performance in harsh environments. The basic physics used in Zettlex sensors is similar to inductive proximity switches but the Zettlex technique allows absolute position measurement in various geometries including rotary, linear, 2D and 3D. Rotary sensors can measure over a full 360 degrees in diameters ranging from 12 – 1200mm. Inductively resonant linear position sensors range from 0,1 to 2000mm. On this web-site we tend to use the term ‘sensor’ but some might refer to Zettlex products as transducers, encoders, resolvers, detectors or transmitters. Similarly we also use the term ‘position’ but some might refer to angle, rotary, multi-turn rotary, linear, curvi-linear, displacement, location. We simply use the term speed as the time derivative of position but some might use the term velocity. Whilst we measure position directly, such measurements can be used to measure servo position, force, wear, weight, vibration, stress, strain, pressure or even temperature by virtue of thermal expansion or contraction. There are a myriad of scientific techniques to measure position including potentiometers, magnetic encoders, magnetostrictive transducers, Hall effect sensors, optical encoders, optical scales, magnetic scales, LVDTs, RVDTs, LVITs, RVITs, synchros, resolvers, pancake resolvers, capacitive transducers, capacitive encoders, electric encoders, Inductosyns, reed switches and magnetoresistive devices. Zettlex inductive position sensors offer high precision, high reliability, compact form and lightweight. Since the sensors are made from PCBs it is relatively easy to engineer a device to suit customer applications and much of Zettlex’s production is for OEM specific sensors that are used in industrial, defence, medical, aerospace, petrochemical, oil and gas applications. We make lots of inductive resonance position sensors for pan and tilt camera controls (PTZ), electro-optic equipment (EOI), gunnery systems (azimuth and elevation controls), weapons control systems, unmanned aerial vehicles, linear actuators, rotary actuators, ATEX equipment, steering angle sensors, torque sensors, valve controls, servo control, motor encoders, missile seekers, missile fin control, hydraulic cylinders, ball screws, joysticks, medical robots, industrial robots, rotary joints, radar antenna, antenna pointing systems, solar pointing devices, valve transmitters, remote control weapons systems (RCWS) and direct drive motor controls. Our sensors have a wide variety of interfaces – both analogue and digital – including 0-5V, 0-10V, 4-20mA, A/B pulses, A/B/Z reference, sin/cos, 1V pk. to pk. sin/cos, HART, CAN, RS232, RS422, RS485, SPI, I2C, SSI, Namur, power line carrier. Electrical supplies range from 3,3V to mains. Some of our standard products such as LINTRAN and IncOder are available directly from our web-site www.zettlex.com. OEMs should contact Zettlex directly to discuss requirements especially if there are safety, certification or aerospace requirements such as ATEX, SIL, DO-178, DO-254, duplex or triplex electrical redundancy. We specialise in providing reliable fit, form and function replacements for existing problematic devices – especially potentiometers, electric encoders and pancake resolvers.
Summary
This document aims to provide technologists with a basic understanding of the operating principles, design rules and potential applications for Zettlex ST (‘Short Target’) Technology.
Zettlex ST Technology is a non-contact displacement sensing and identification technique.
The fundamental operating principle utilises the physical phenomenon of radio frequency [RF] interaction between an Antenna and a Target. An Antenna containing Transmit and Receive circuits (usually tracks on a printed circuit board) is supplied with an RF signal. A low power, alternating electromagnetic RF field is formed in the region of the Antenna’s Transmit Circuit. When an inductive Target enters that field, the Target emits its own electromagnetic field that can be sensed by the Antenna’s Receive circuits (usually tracks on the same PCB as the Transmit Circuit). The Received signal indicates the Target’s identity and position relative to the Antenna.
Whilst the fundamental physical phenomena are well known, ST Zettlex provides a particularly low cost, high performance sensing solution which can be readily integrated in to host systems. Most ST sensors are produced using simple printed circuit boards or wire forms and, as such, can be produced by a variety of standard, widely available manufacturing techniques.
In most instances, the Sensor’s electronics are cost effectively produced using a relatively simple circuit of standard, discrete electronic components. Application specific integrated circuits are most cost effective for high volume applications (>300kunits/yr),
Zettlex ST Targets and Antennae can be conformally coated or fully encapsulated if required. Consequently, ST sensors are extremely robust and are generally unaffected by foreign matter, moisture, humidity, liquids, temperature, extraneous AC/DC fields or mechanical misalignments between Target and Antenna. Generally, ST sensors are as robust as their component materials.
Zettlex ST Technology is suited to a wide variety of sensing geometries. Dynamic ranges are typically from 1mm to 10m. Applications are typically in one of 3 main groups: displacement sensors, user interfaces or identification systems. There is also a wide variety of markets for such applications including automotive, consumer electronics, aerospace, medical, industrial controls and actuators.
ST Technology is patent protected.
Table of Contents
1. Introduction................................................................................................. 4
2. Aim........................................................................................................... 4
3. Background Science..................................................................................... 5
3.1 Magnetic Field Due To An Electric Current.................................................... 5
3.2 Magnetic Field Strength............................................................................ 5
3.3 Electromagnetic Induction........................................................................ 6
4. Operating Principles...................................................................................... 8
5. Main Components Descriptions....................................................................... 9
5.1 Target.................................................................................................. 9
5.2 Antenna............................................................................................... 9
5.3 Electronics Module................................................................................. 9
6. Functional Performance............................................................................... 10
6.1 Affects of Mechanical Offsets & Tolerances.................................................... 11
7. Non-Functional Performance......................................................................... 12
7.1 Temperature........................................................................................... 12
7.2 Humidity & Moisture.................................................................................. 12
7.3 Chemical Resilience................................................................................. 12
7.4 Lifetime.................................................................................................. 12
7.5 Shock & Vibration..................................................................................... 12
8. Sensing Geometries...................................................................................... 13
9. Multi Sensor Systems................................................................................... 17
10. Example Specifications................................................................................ 19
11. Design Guidelines....................................................................................... 20
12. Comparison with Other Technologies.............................................................. 21
13. Applications............................................................................................... 22
13.1 General Attributes.................................................................................. 22
13.2 Specific Applications Examples................................................................. 23
14. Frequently Asked Questions.......................................................................... 24
1. Introduction
Zettlex exploits proprietary, non-contact sensing technologies across a variety of applications and sectors. We offer robust, reliable sensors at affordable prices. Our customers are typically original equipment manufacturers or electronic/electrical system manufacturers to whom we sell sensors, engineering contracts or pre-programmed micros.
2. Aim
This document is a technology description intended to provide technologists with a basic understanding of the operating principles, design rules and potential applications for ST (Short Target) Zettlex technology.
3. Background Science
If you're an experienced electrical engineer or physicist you can skip this section and go directly to Section 4. The physical principles behind Zettlex ST Technology are well established and covered by some fundamental physical laws:
3.1 Magnetic Field Due To An Electric Current
When a conductor carries a current, a magnetic field is produced around that conductor – a phenomenon discovered by Oersted atCopenhagenin 1820. He found that when a wire carrying an electric current was placed above a magnetic needle, the needle was deflected clockwise or anticlockwise depending on the direction of the current.
Thus it is found that if we look along the conductor and the current is flowing away from us, as shown by the cross inside the conductor in Figure 1, the magnetic field has a clockwise direction and the lines of magnetic flux can be represented by concentric circles around the wire.
Figure 1. Magnetic flux due to current in a straight conductor
3.2 Magnetic Field Strength
Ampere’s Law, states that the magnetic field strength in free space, H, at distance r from an infinitely long straight wire carrying a current I is given by the equation:
Figure 2. Ampere’s Law
The field produced by an infinitely long conductor is easy to understand. When the conductor is wound in to a loop or series of loops the field pattern is more complex. The field around a loop can be generally classified in to 3 areas:
- Wire Field – very close to the surface of the conductor. This field has high field strength and the pattern is predominantly that of an infinitely long straight conductor irrespective of the conductor’s actual shape. This field – given its tiny distance from the conductor’s surface - is generally not considered when discussingZettlex ST technology.
- Near Field – the Near Field is the most important of all three areas for us to consider when consideringZettlex ST technology. It is of relatively uniform field strength. The Near Field for a current carrying conductor formed in to a circular loop of radius r would typically extend to a limit above and below the loop of 0.5r
- Far Field – away from the conductor. The far field is that region beyond the near field and extends to infinity. The field strength drops off according to the cube of the distance from the current carrying conductor arranged in a simple loop.
If a current carrying conductor is wound to form a loop, the field from any such circuit is increased by the number of circuits, N, in any such loop. The field from the coil is proportional to N and the current in the coil; the product NI is often referred to as the ‘amp-turns’ in the circuit.
3.3 Electromagnetic Induction
On 29 August 1831, Michael Faraday made the discovery of electromagnetic induction, namely a method of obtaining an electric current with the aid of magnetic flux. He wound two coils on an iron ring and found that when a switch was closed to allow current to flow in the first coil a deflection was obtained in a galvanometer in the second coil. Further, when the switch was opened the galvanometer was deflected in the reverse direction. He proposed that one current was inducing a current to flow in the second.
A few weeks later, in a separate experiment, he found that when a permanent magnet was moved relative to a coil, a galvanometer was deflected in one direction and in the opposite direction when the magnet was moved away from the coil. It was this experiment that convinced Faraday that electric current could be produced by the movement of a magnetic flux relative to a coil. Faraday also showed that the magnitude of the induced e.m.f. is proportional to the rate at which the magnetic flux passing through the coil is varied.
If we consider two coils - a transmit coil (Tx) and a receive (Rx) coil – then we can see that the following equation would apply:
Figure 3. Induction of current in a receive coil from a transmit coil.
VRX= - K dITX
dt
Where:
¨ VRXis the voltage induced in the Receive coil
¨ K is the mutual inductance coupling factor depending on the coils relative areas, geometry, distance, and relative number of Circuits.
¨ dITX/dt is the rate of change of current in the Transmit coil.
4. Operating Principles
A Zettlex ST Sensor comprises three main operating elements: Target, Antenna and Electronics Module:
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Signal |
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Measurement axis |
Figure 5. ST Sensor Schematic.
The Target is a passive device usually made from a piece of printed circuit board (PCB) and requires no electrical connection.
The Antenna comprises at least one Transmit Circuit and at least one Receive Circuit.
The Transmit Circuit is supplied from the Electronics Module with an RF signal.
An electromagnetic field is generated around the Transmit circuit. When the Target enters the field, the Target produces its own electromagnetic field. Receive Circuits in the Antenna sense the field produced by the Target. The Antenna Circuits are wound on a pitch, L, along the measurement axis.
Analysis of the signals in each of the Receive Circuits uniquely defines the Target’s position along the measurement axis.
A number of Targets may be sensed at any one time from a single Antenna.
There is no change in measurement value should the Target move, within limits, in axes normal to the measurement axis. The upper limit of the Target’s movement normal to the measurement axis is equivalent to the limit of the Near Field generated by the Antenna's Transmit Circuit.
5. Main Components Descriptions
5.1 Target
The Target is a passive circuit formed by a simple winding or a set of tracks on a printed circuit board.
Targets can be conformally coated (varnished), potted or insert moulded in to an injection moulding if environmental conditions necessitate.
5.2 Antenna
The Antenna is typically a planar arrangement of Transmit and Receive Circuits. Each of the Circuits is electrically insulated from each other and arranged along the measurement axis of the Antenna.
Typically the Circuits are embodied as tracks on a printed circuit board – most usually two-sided FR4 grade PCB with plated via holes connecting each part of each Circuit. Simple wire windings or printed thick films of conductive ink can also produce Antennae.
5.3 Electronics Module
The Electronics Module comprises a power supply (including over voltage protection if required), a Transmit circuit (including a crystal oscillator), a receive circuit, a microcontroller and an electrical output. Typical power supplies are 5 +/- 0,5V DC and a current requirement of
6. Functional Performance
Displacement Sensors are typically characterised by three main parameters:
¨ Resolution
¨ Linearity
¨ Repeatability.
In the case of Zettlex ST Sensors these main parameters can be altered by the design of the Antenna’s Circuits. In a simple Sensor, a single pair of Circuits is used of pitch L:
Figure 7. Simple single pitch device.
In this simple, single pitch Sensor the
¨ Resolution is <0,05%L
¨ Linearity is <0,5%L
¨ Repeatability is <0,1%L.
For example, a 100mm long simple, single pitch Sensor has a resolution of
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L2 |
Figure 8. Multiple pitch device.
In this example L2 = 0,1L. A 100mm long Sensor produced from 10 pitches of 10mm long, has a resolution of
Thus it can be seen that by replacing single or coarse Circuits by finer pitch multiple Circuits, the Sensor’s performance is substantially improved. However, the Sensor becomes incremental rather than absolute because of the measurement ambiguity of the serial pitches.
In order to achieve the improved performance and maintain absolute position measurement, the shorter pitch Circuits are intertwined with the single pitch Circuit so as to enable a coarse position and fine position measurement. The Circuits are typically made on a common PCB.
Such patterns are possible on all Sensor geometries.
Sensor linearity is maintained over about 90% of the total length of any linear, curvi-linear or 2D Sensor Circuits and over a full 360 degrees for any rotary Sensor Circuits.
6.1 Affects of Mechanical Offsets & Tolerances
Unlike many sensors,Zettlex STsensors are generally unaffected by mechanical offsets and assembly tolerances. In the following example X is the measurement axis. Measurement performance is unaffected, within limits, by variations of the Target’s position in the Y or Z-axis, so long as the majority of the Target is within the Antenna’s Near Field. Furthermore, slight rotation of the Target about the X or Z-axis does not alter measurement performance. Only rotation of the Target about the Y-axis affects the measurement. Most usually the Target’s rotation in this axis is constant and is therefore a constant rather than a variable offset.
Figure 9. Axes for a linear ST Sensor.
In instances where the Target is likely to rotate in multiple axes, the Target’s resonant circuits can be designed so as to negate such rotational affects.
7. Non-Functional Performance
7.1 Temperature
The fundamental operating principles of ST technology are not affected by temperature. That means ST Sensors can reliably operate in relatively low or high temperatures. Practically, the materials, from which the Sensor’s components are produced, limit the operating and storage temperatures. Most frequently, the effective temperature range is limited by the electronic components at –40 to 85 or 125 Celsius (i.e. industrial or automotive ranges). Importantly, it should be noted that the Sensor’s electronics can be displaced away from the Antenna. This enables the Sensors to be designed such that only the Antenna and Target are placed in harsh temperature environments whilst the Electronics can be situated in a more benign environment. Elevated temperatures can be accommodated with the use of suitable substrates for the Antennae and Targets.
7.2 Humidity & Moisture
Humidity or moisture does not affect the fundamental operating principles of ST Sensors. That means ST Sensors can operate in relatively low or high humidity environments – or even submersed in a liquid. Practically, the materials, which package or enclose the Sensor determine resilience to liquids. Most frequently, the Sensor components are conformally coated with varnish. Alternatively, the Sensor components can be epoxy encapsulated or insert moulded. Submersion in salt water or petrol does not affect Sensor performance.
7.3 Chemical Resilience
The fundamental operating principles of ST technology are not affected by any chemicals. That means ST Sensors can operate in relatively harsh chemical environments. Practically, the materials, which package or enclose the Sensor determine resilience to liquids. Most frequently, the Sensor components are conformally coated with varnish. Alternatively, the Sensor components can be epoxy encapsulated or insert moulded.
7.4 Lifetime
The lifetime of a ST Sensor is determined by the lifetime of the components carrying the Target and Antenna.
7.5 Shock & Vibration
The performance of a ST Sensor with vibration or shock is determined by the performance of the components carrying the Target and Antenna.
8. Sensing Geometries
The following section provides an overview of the most common geometries of ST Sensors. In all instances position measurement is absolute, however, the Sensors can be configured to provide incremental signals if required.
Rotary Sensor – Co-Axial Target & Antennae. The maximum stand off distance between Target and Antennae is about ¼ of the effective (electrical) diameter of the Antennae or Target. The Sensor may be constructed with a through shaft (of conductive or non-conductive material) or in an ‘end of shaft’ arrangement with no through shaft. Position measurement is absolute from 0 to 360 degrees with no measurement ‘blips’ at crossover from 0 to 360 degrees. Typical application: through shaft rotary encoder for a user interface.
Rotary Sensor – (Slightly) Non-Co-Axial Target & Antennae. The maximum stand off distance between Target and Antennae is about ¼ of the effective diameter of the Antennae or Target. The maximum axial offset depend on a number of factors but generally, may be taken as varying between 0-10% of the diameter of the Antenna or Target without significantly affecting measurement performance. Position measurement is absolute from 0 to 360 degrees with no measurement ‘blips’ at crossover from 0 to 360 degrees. Typical application: end of shaft rotary encoder for motors or drives.
Rotary Sensor – (Grossly) Non-Co-Axial Target & Antennae. The maximum stand off distance between Target and Antennae is about ¼ the diameter of the effective diameter of the Target. The centre of rotation of the Target may vary within the limits of the Antenna such that the Target’s circumference does not approach the periphery of the Antenna. Position measurement is absolute from 0 to 360 degrees with no measurement ‘blips’ at crossover from 0 to 360 degrees. This geometry is not suitable for measurement rates of >50Hz. Typical application: end of shaft rotary Sensor for suspended or sprung shafts.
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Linear Sensor.The maximum stand off distance between Target and Antennae is about 1/3 of the effective width of the Antennae or Target. The maximum offset of the Target at right angles to the measurement axis (but coplanar with Antenna) depends on a number of factors but may be taken as varying between 0-10% of the width of the Antenna or Target without affecting measurement performance. Position measurement is absolute but should be limited to
Curvi-Linear Sensor [A].The maximum stand off distance between Target and Antennae is about 1/3 the width of the effective width of the Antennae or Target. The maximum offset of the Target at right angles to the measurement axis (but coplanar with Antenna) depends on a number of factors but may be taken as varying between 0-10% of the width of the Antenna or Target without affecting measurement performance. Position measurement is absolute but should be limited to
Curvi-Linear Sensor [B].The maximum stand off distance between Target and Antennae is about 1/3 of the effective width of the Antennae or Target. The maximum offset of the Target at right angles to the measurement axis (but coplanar with Antenna) depends on a number of factors but may be taken as varying between 0-10% of the width of the Antenna or Target without affecting measurement performance. The Sensor can curve a full 360 degrees if required, wherein no measurement blip will occur at 0 to 360-degree transition. Position measurement is absolute but should be limited to
Roll & Pitch Sensor. The maximum stand off distance between Target and Antennae is about 1/3 the width of the effective width of the Target. This limit therefore affects the typical measurement range from 0 to +/-45 degrees for each rotational axis. Position measurement is absolute. Typical application: Tilt measurement.
Zettlex ST Electronic Modules can be designed to multiplex across a number of Sensors. More traditional techniques such as Hall affect or capacitive sensors do not permit this because the required electronic processing has to be positioned adjacent to the sensing point. WithZettlex STtechnology, however, it is possible to position the Electronics Module away from individual Antennae and Targets. This is because the Received signals have relatively high amplitudes and the subsequent signal processing is robust. In turn, this permits multiple Sensors to be energised from, and supply signals to, a central Electronics Module.
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Electronics Module |
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Signal |
Figure 19. Schematic of multi-sensor system controlled by one Electronics Module.
Since Targets and Antennae are relatively inexpensive to produce it makes good economic sense to multiplex the Electronics Module. This amortises the Module’s cost across multiple Sensors, thus bringing the costs/Sensor down to its lowest possible level.
Note that the interconnections between Sensors & Electronics Module can also be inexpensively produced. Typically the interconnections are either tracks on a PCB, a flexi-PCB interconnect,CAT5 cable or flexible tracks in flexi-rigid hybrid PCB.
A further point worthy of note is that it makes most economic sense to integrate the electronic components in to a host or motherboard. This allows the electronics component, assembly and test costs can be minimised.
The maximum number of Sensors per Electronics Module is determined by the maximum permissible response time from a given Sensor input. If we consider the example of a system with a measurement cycle time of say 1 milliseconds per Sensor and a maximum permissible response time of 25 milliseconds, then the maximum number of Sensors per Electronics Module is 25. This limit can be increased by the use of more sophisticated multiplexing algorithms – for example, sampling the most frequently used Sensor inputs more frequently and vice versa.
The maximum distance that a Sensor can be displaced from the Electronics Module is determined by 3 main factors:
- Physical size of the Sensor,
- Coupling factor between Target & Antenna,
- EMC/regulatory environment.
Generally, if the Target and Antenna are large with a relatively low stand off distance (and hence good coupling factor) then distances between Sensor and Electronics Module of several metres are permissible. EMCrequirements need to be considered in the system design not because of the Sensor’s susceptibility but rather due to electromagnetic emissions.
EMCissues on long cable or interconnect lengths can be mitigated by the use of shielded, twisted pair cable and connectors. A further option is to route any interconnections in earthed metal conduit. Of course, it is preferable to avoid the use of shielded cables etc. due to the additional costs. By way of example, a 2m long unshieldedCAT5 cable is acceptable within a consumer electronics environment regulated by EN68000, for example.
A requirement to measure the position of multiple Targets does not necessarily require the use of multiple Antennae. It should be noted that a single Antennae can track multiple Targets. 8 targets per Antenna is a sensible limit without the need for increasing the complexity or costs of a standard Electronics Module.
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Signal |
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Figure 20. Multiple Targets with single Antenna.
A Zettlex STsystem containing multiple targets with one Antenna plus further additional Target and Antenna pairs is permissible.
When multiple Sensors or Targets or Antennae are controlled by a central Electronics Module it is, of course, beneficial to consider the use of a data stream output - rather than multiple 0-5V DC or PWM outputs - to minimise connector and cabling costs.
10. Example Specifications
The following should be taken as examples only rather than limits:
25mm Diameter Rotary Sensor (3x120O degree pitch)
¨ Antenna size: 25mm O.D. and 5mm I.D.
¨ Target size: 25mm O.D. & 5mm I.D.
¨ Target:Antenna stand off: 3mm +/- 1mm
¨ Target:Antenna parallelism: <5o
¨ Measurement: Relative over 120ocontiguous sectors
¨ Resolution: 0,12 degrees
¨ Linearity:
¨ Repeatability: 0,24o
¨ Measurement bandwidth: 1000Hz
¨ Concentricity:
75mm Diameter Rotary Sensor (8x45O degree pitch + 360o single pitch))
¨ Antenna size: 75mm O.D. and 13mm I.D.
¨ Target size: 75mm O.D. & 13mm I.D.
¨ Target:Antenna stand off: 10mm +/- 2mm
¨ Target:Antenna parallelism: <5o
¨ Measurement: Absolute over 360o
¨ Resolution: 0,05 degrees
¨ Linearity:
¨ Repeatability: 0,02o
¨ Measurement bandwidth: 1000Hz
¨ Concentricity:
150mm Linear Sensor (multiple 40mm pitches)
¨ Antenna size: 200mm long & 20mm wide
¨ Target size: 25mm long & 20mm wide
¨ Target:Antenna stand off: 7mm +/- 2mm
¨ Measurement: Absolute over 150mm
¨ Resolution: 0,15mm
¨ Linearity: <0,5%
¨ Repeatability: 0,3mm
¨ Measurement bandwidth: 1000Hz
150mm Linear Sensor (relative)
¨ Antenna size: 200mm long & 20mm wide
¨ Target size: 25mm long & 20mm wide
¨ Target:Antenna stand off: 7mm +/- 2mm
¨ Measurement: Relative over 40mm contiguous segments
¨ Resolution: 0,04mm
¨ Linearity:
¨ Repeatability: 0,08mm
¨ Measurement bandwidth: 1000Hz
11. Design Guidelines
If you plan to use a ST Field Sensor, the following is an aide memoire:
- Dynamic range – measurement geometry and distance should be specified. If it’s a linear, curvi-linear or 2D Sensor, allow the Antenna to extend beyond the measurement limits by at least 10% of the dynamic range at either end.
- Resolution – fineness of measurement should be specified. Measurement resolutions of significantly
- Repeatability & Linearity – degree of repeatability and linearity should be specified. Measurement repeatability of significantly
- Absolute or incremental – if the host system requires position measurement at power up, without a self-calibration step to known positions, then absolute measurement should be specified.
- Distance between Target & Antenna – measurement accuracy is not affected by slight variation in stand off distance between Target & Antenna, as long as the Target never leaves the Near Field.
- Temperature range – consider the temperature range for storage and operation. If the temperatures are extreme at the sensing point, consider placing the electronics away from the Sensor to a more benign environment.
- Humidity and moisture – if there is high humidity, condensation or submersion then sealing or encapsulation should be considered
- Distance of Sensors from Electronics – Generally, the shorter the distance, the less problematic anyEMC issues. At any distance >300mm,EMC issues must be considered with possible solutions of multiple frequency Sensors, twisted pair cables, screened cables, screened connectors, metal enclosures, metal conduit etc.
12. Comparison with Other Technologies
The following table gives a rough comparison ofZettlex ST technology with other technologies – it is not intended as an exhaustive discussion:
13. Applications
13.1 General Attributes
Zettlex STsensors are not intended to be universally applicable. In some instances a simple switch will provide the design engineer with the optimal cost/performance solution. Nevertheless, in many other instances Zettlex ST Sensors are more suitable to a given application than other technologies such as Hall affect, optical Sensors, etc.
Zettlex ST Sensors have a number of unusual attributes
¨ multiple Sensors can be controlled by a single set of electronics
¨ they are extremely robust in harsh environmental conditions in terms of moisture, foreign matter or temperature extremes
¨ they are insensitive to AC/DC fields
¨ they are tolerant of mechanical offsets and tolerances
¨ they are accurate
¨ they provide absolute rather than incremental position measurement
¨ they can identify a number of different targets and measure their position independently and concurrently
¨ they are suitable for unusual or complex sensing geometries
¨ they have long-life.
Typically, Zettlex ST Sensors are to be used when two or more of the above attributes are applicable to a sensing project facing a design engineer.
13.2 Specific Applications Examples
Actuators
Aileron controls
Analogue gauges
Angle sensors
Antenna tracking
Anti-counterfeit devices
Audio controls
Automatic teller machines
Automation equipment
Ball screws
Boilers
Brake sensors
Brake wear sensors
Brake wear sensors
Burners
Climate controls
Cockpit controls
Component ID
Consumer electronics
Cookers
Cooking ranges
Cooktops
Dials
Dial indicators
Direction indicators
Dishwashers
Displacement sensors
Door travel sensors
Elevators
End of shaft encoders
Fitness equipment
Flow sensors
Food mixers
Fuel level sensors
Fuel metering
Games
Gauges
GMR sensor replacements
Guided vehicle tracking
Gunnery sights
Hall affect replacements
Headlamp level controls
HVAC sensors
Hydraulic actuators
Hydraulic valves
ID tags
Inclinometers
Inductosyn replacements
Industrial control panels
Joysticks
Kitchen goods
Lifts
Lighting controls
Limit switch replacements
Linear actuators
Liquid level sensors
Load sensors
LVDT replacements
Machine tools
Magnetostrictive replacements
Mining equipment
Missile guidance
Motion controllers
Motor encoders
Odometers
Packaging equipment
Palletisers
Paper thickness sensors
Pedal sensors
Pen sensing
Petrochemical sensors
Plotter controls
Pneumatic actuators
Pneumatic valves
Pressure sensors
Printer write heads
PRNDL sensors
Proximity sensors
Push buttons
Radar controls
Ride height sensors
Robots
Roll & pitch sensors
Roll, pitch & yaw sensors
Roller separation sensors
Rotary encoders
RVDT replacements
Safety switches
Seating instrumentation
Security tags
Servo motors
Servo motors
Shaft encoders
Sheet feeders
Skis
Sliders
Speed sensors
Sports equipment
Steering angle sensor
Steering column controls
Steering torque sensors
Stepper motors
Strain measurement
Suspension dampers
Suspension sensors
Tachometers
Tamper evident devices
Throttle controls
Tilt sensors
Torque sensors
Toys
Traction control
Transmission sensors
User interface elements
Utility meters
Valves
Valve Actuators
Velocity sensors
Vibration sensors
Washing machines
Windscreen wipers
Weight sensors
Wheel sensors
Workpiece ID
14. Frequently Asked Questions
How far can a Target be away from the Antenna?
The Near Field produced by the Antenna’s Transmit circuit determines the limit. As an example, if a linear Antenna is 300mm long by 30mm wide, with a Transmit circuit arranged along the periphery of the Antenna, then the Near Field extends to a maximum distance of 15mm from the plane of the Antenna. A sensible design limit would be to specify a distance of Target from Antenna of <12mm.
Can a ST Field Sensor operate through a metal shield?
In principle, a metal shield can be inserted between a Sensor’s Target and an Antenna. Generally, such an arrangement is not preferred due to the heavy signal losses caused by such an arrangement. The skin depth through which the excitation signals can permeate limits the thickness of the metal shield. The lower the excitation frequency, the greater the thickness of permissible metal. The maximum thickness of metal depends on the actual metal. If a metal shield is to be used then non-magnetic stainless steel is most preferred with aluminium, steel, copper or brass least preferred. Practically, metal thicknesses of <
How many identities can a Target carry?
In theory, a Target can carry an infinite number of identities. Practically, a Target is limited to about 8 frequencies and hence 8 identities. However, an object can carry multiple Targets of differing frequency - hence multiplying the possible number of identities. Furthermore, the relative distance and orientation of the Targets can be sensed by an Antenna, thus multiplying the number of identities still further.
What maximum temperature can a Zettlex ST Sensor cope with?
The fundamental operating principles are not affected by temperature. That means Zettlex ST Sensors can operate in relatively low or high temperatures. Practically, the materials, from which the Sensor’s components are produced, limit the operating and storage temperatures. Most frequently, the effective temperature range is limited by the electronic components at –40 to 85 or 125 Celsius (i.e. industrial or automotive ranges). Importantly, it should be noted that the Sensor’s electronics can be displaced away from the Antenna. This enables the Sensors to be designed such that only the Antenna and Target are placed in harsh temperature environments whilst the Electronics are placed in a more benign environment away from, or insulated from, the harsh conditions. Ceramic or high temperature epoxy substrates for the Antennae and Targets can be used to increase temperature limits.
How far can the Electronics be away from the Antenna?
The maximum distance between Electronics and Antenna is determined by two main factors – the coupling factor between Target & Antenna and the application’s electromagnetic environment orEMCrequirements. The greater the signal amplitudes in the Antenna’s Receive circuits and the more relaxed theEMCenvironment, the greater the permissible displacement between Electronics and Antenna. The use ofEMCshielded cable between Antenna and Electronics generally increases the maximum permissible distance. In consumer electronics applications a distance of 2m is achievable without the use of shielded cable between Electronics and Antenna. Zettlex can advise on maximum distances given a particular Sensor geometry, size and relevantEMCdata.
Do magnets affect Zettlex ST Sensors?
Generally, Zettlex are unaffected by DC magnetic fields. However, if the magnets are within the Sensor’s Near Field then they will tend to distort the Antenna’s field by providing an ‘easy route’ for the magnetic flux. This can be accommodated in the design of the Sensor by modifying the arrangement of the Transmit and Receive circuits.
Do metal objects affect Zettlex ST Sensors?
Metal objects outside the Sensor’s Near Field have practically no affect on the Sensor. However, metal objects within the Near Field tend to distort the Magnetic pattern. Again, as with magnets these can be accommodated in the design of the Antenna. Distortion affects are minimised if the metal objects are symmetrical e.g. a metal shaft through the centre of the Sensor.
What emissions do Zettlex ST Sensors produce?
By their fundamental nature Zettlex ST Sensors do produce electromagnetic emissions. However, these emissions are small and in practice, such emissions are invisible in the Far Field due to the natural, rapid fall off of the field. Given the low emissions levels Zettlex ST Sensors are suitable for automotive or defence applications where permissible emission levels are particularly stringent.
Are Zettlex ST Sensors susceptible to emissions from other sources?
Zettlex ST Sensors are generally not susceptible to emissions from other sources due to a number of factors: - the Receive circuits are arranged as balanced quadropoles (thus negating the affect of incoming plane waves), the signal from the Target is at a highly specific frequency and the Sensor uses synchronous detection. Zettlex ST Sensors are suitable for automotive or defence applications where permissible emission susceptibility is particularly stringent
How much power do Zettlex ST Sensors need?
A typical power requirement is 5V and
Can the Zettlex ST Sensor electronics be part of a host system’s electronics?
Yes. It is possible in some instances of relatively simple machine control to integrate machinery control software in to the microprocessor containing the Zettlex ST Sensor software. Power supply, frequency generation etc. can also be shared between host and Sensor system.
How many Sensors can a Zettlex Electronics Module handle?
The maximum number of Sensors per set of electronics is determined by the maximum permissible response time per Sensor. If we consider the example of a Zettlex ST Sensor taking 1 milliseconds per measurement and a maximum response time of 250 milliseconds then with a simple multiplexing scheme the maximum number of Sensors is 250. This number can be increased with a more sophisticated multiplexing algorithm, for example, sampling the less frequently used or less important Sensors less frequently. A ST Zettlex Electronics Module can also handle inputs from other elements such as switches.
Can Zettlex sensors of different geometries be controlled by a single set of electronics?
Yes. The standard Zettlex software can be parameterised to control multiple Sensors of various geometries.
