The eddy current linear position sensors utilise a reference coil for producing a magnetic field in a target. This reference coil is also used for monitoring the field in the neighbouring sensing coil to find out the distance from the target. As the target starts getting closer to the sensor, the magnetic field gets disrupted and this disruption is sensed by the other coil.

Eddy current linear position sensors also determine the variations in the magnetic field due to the presence of close conductive objects. Field detection and generation information is offered in the range of kHz to MHz. As these sensors operate by the interruption of the magnetic field, it is possible to have ferrous or nonferrous, magnetic or non-magnetic targets.

How to select the appropriate eddy current linear position sensors

The range that eddy current linear position sensors can measure and its sensing frequency are two of the most important specifications to consider. The sensing frequency is actually the frequency range on which the device operates. Static resolution of the eddy current linear position sensors is also an important consideration.

The smallest rise of the quantity that can be recognised is known as the resolution. The static resolution tells you about the change in quantity that is required for the sensor to determine the change. In order to determine the small changes in position, you will need a sensor with a very small resolution.

Electrical output offered by the eddy current linear position sensors can be computer signals (serial or parallel), digital, analogue voltage, frequency or current. By considering these things, you can easily get the right eddy current linear position sensor to suit your requirements.

Sensor transmitters are signal conditioning or measurement packages that offer a standard and calibrated output from transducers and sensors. The output types of sensor transmitters include variable voltage levels, pulse or frequency signals, current loops, counters or timers, variable resistance outputs and relays.

The sensor transmitters can also offer transistor-transistor logic (TTL) and radio frequency (RF) signals output. Current loop like 4 – 20 mA are ideal for sensing signals over long distances. The current imposed on the output circuit is usually proportional to its measurement. Feedback is also used for offering an appropriate current, irrespective of the impedance and its line noise.

Modulated frequency or frequency output of sensor transmitters include;

• Pulse trains
• Sine waves
• Frequency modulation (FM)
• Amplitude modulation (AM)

Types of input received by sensor transmitters

The sensor transmitters can receive three types of input; sensor inputs, signal inputs and from special devices. The signal inputs of sensor transmitters include AC current, DC current, AC voltage and DC voltage. They also include charge and frequency signals that require amplification and filtering.

Sensor transmitters can also receive inputs from thermocouples, resistance temperature detectors (RTD), accelerometers and thermistors. Strain gauges are another means through which sensor transmitters can receive input. Most strain gauges utilise a Wheatstone bridge from both rotary and linear variable differential transformers (RVDT and LVDT).

Signal inputs from special devices include encoders and signal per cycle counts from tachometers and counters. Switches, relays, clocks, timers can also provide special inputs to these sensor transmitters.

Level switches are often used for detecting interfaces between liquids, or to determine powder and liquid levels. These level measurements are often indicated through an electrical switching action. The point level switch measures the level of a container that has gone over or reached a pre-determined point.

The switching mechanism is vital for continuous level switches. The multiple point switches can also be incorporated together to offer a stepped version at a constant level. The level switches can be used as control switches or as alarm devices to turn something off or on, like sending signals to a valve actuator or pump.

Technologies used for measuring include;

• Air bubble technology
• RF or capacitive admittance
• Electrical resistivity or conductivity
• Differential pressure
• Pressure membrane
• Optical units
• Magnetic or mechanical floats
• Radio frequency
• Sonic or ultrasonic
• Tuning fork or vibration

Types of level switches

Level switches have a switched output that can either be solid state, electromechanical state, normally closed or normally open. Options for throws and poles are also available. Most level switches either have one or two throws or poles. Some manufacturers even produce custom level switches for specialised applications.

When purchasing a level switch, you need to consider the measuring range that it offers. The ratings for voltage or current of the level switch are also an important consideration. Depending on the application requirements, level switches can be mounted in many different ways. Level switches can be mounted on the side, top or the bottom of the container that holds the substance which is to be measured.

Liquid level sensors are mostly used for detecting interfaces or liquid levels between liquids like water and oil or solid and liquids. These sensors can be defined as a transducer, sensor, or an integrated system with control and instrumentation capabilities.

Depending on the application, you can choose between point level and continuous sensing. The point level sensors usually turn off the system or trigger an alarm depending on a specific limit. There are some applications that depend upon continuous liquid level monitoring. It can use different methods including vibration, ultrasound and pressure for continuous liquid level monitoring.

Different types of liquid level sensors

The differential and pressure membrane liquid level sensors determine the pressure or changes in pressure in a vessel like a storage or holding tank. There are sonic / ultrasonic liquid level sensors that determine the length of time taken for a reflected sound wave to return back to the transducer.

Tuning / vibrating fork liquid level sensors utilise a piezoelectric crystal or other type of technology for vibrating a probe. They also continuously monitor the absence, presence, decrease or increase of that vibration.

In some applications, it is essential to determine the liquid level without having any direct contact with the media. Applications that include highly corrosive liquid use non-contact meter technologies like sonic / ultrasonic liquid level sensors or/and microwave / radar liquid level sensors may be the most favourable options.

When it comes to choosing ultrasonic liquid level sensors, you need to consider the temperature, surface properties and media types.

Ultrasonic transducers transmit and receive waves for numerous types of sensing. They convert the high frequency sound wave energy into an ultrasonic range. When these sound waves are focused on a target, the echo is read by these sensors.

Ultrasonic transducers determine a specific variable like speed, distance level or proximity in applications such as counting, security applications, non-destructive evaluation, web break detection, and welding and cutting. They operate at a resonant frequency with numerous construction options, power levels and beam patterns.

Some important specifications of ultrasonic transducers

The ultrasonic transducers have numerous important specifications. Transmitting frequency is the functional frequency range of the device. The bandwidth is actually the difference between high and low operational frequency limits.

Rated signal power of ultrasonic transducers are other important specifications. Transmit sensitivity of the ultrasonic transducers is the ratio of sound pressure created to input voltage. On the other hand, receive sensitivity is the ratio of the output voltage that is produced over the sensed sound pressure.

The beam angle is the completely incorporated angle of the ultrasonic beam. A lower frequency transducer usually produces a wider beam whereas a high frequency ultrasonic transducer produces a narrow beam. The beam angle of the ultrasonic transducer can be influenced using a transducer housing construction.

The angle beam ultrasonic transducer comprises of mounted transparent angle blocks which are used for flaw detection and weld inspection. They use refracted shear waves for detecting faults throughout the depth of connect areas.

Ultrasonic transducers are available in different configurations used for connecting one or more transducers in a parallel or series.

Liquid level sensors detect interfaces or liquid levels between liquids like water and oil or solid and liquid interfaces. These liquid level sensors are often used in different liquid container monitoring applications including furnaces and heaters, flow line monitoring as well as in other automotive applications, household appliances and control technology.

Different types of liquid level measurement technologies are available including sonic / ultrasonic, optical, pressure membrane, microwave / radar, differential pressure sensing, electrical resistance / conductivity, air bubbler, magnetic / mechanical floats, tuning / vibrating fork, rotation paddle, radio frequency and RF / capacitive admittance.

These level measurements are generally indicated by activating or deactivating an electronic switch like a relay, reed or a solid state switch. Electrical resistivity and conductivity liquid level sensors utilise a low-voltage power source that is generally applied across separate electrodes. A conductive liquid like water or chemical contacting both probes complete the conductive circuit.

Electrical resistance or conductivity is generated when the liquid contacting from both probes complete a conductive circuit. In the majority of cases, the vessel or tank is included in this circuit. The signal can be transmitted to a process controller where the set points have been programmed to close or open valves, and / or to initiate other fluid processes.

Magnetic or mechanical floats are generally used with liquid level sensors. These liquid level sensors can be placed at different points to determine the flow or level of the process liquid. Liquid level sensors are generally used in fuel level measurement applications.

Distance sensors are devices that can detect any object and check if it lies within its range. The distance sensor will usually send a signal to an electronic circuit. This will cause the circuit to perform a necessary action. This might include actions such as opening a door, sounding an alarm or turning on a light. Most distance sensors can detect any object if it comes too close.

Distance sensors are used in various applications such as the ones given below:

Radar – Radar is a type of distance sensor and it uses radio waves or microwaves as a medium to detect objects. These waves are directed towards an object and they are repelled from the surface of the object. These waves are then used to calculate the distance between the radar and the object. The time taken for the wave to return can be measured and used by the application.

Sonar – Sonar uses a distance sensor and works in a way that is very similar to radar. Sonar uses sound as a medium to determine the distance between it and an object. Sonar is used by humans for underwater detection. It was initially inspired by land mammals such as bats that use sonar to detect their prey.

Distance sensors are mainly used in industrial applications. They are available in many different types and hence you need to use one that suits your requirements.

If you ever watched a deep sea diving documentary, you might have wondered how researchers can tell the depth of water without actually getting into it. For those who do not already know, this is done with the help of distance sensors. Generally, distance sensors are non-contact devices. There are different kinds of distance sensors that use different technologies. These include infrared, laser and ultrasonic technologies. Over the last few years, most distance sensors have been using ultrasonic technology to determine distances between the devices and their targets.

How do ultrasonic distance sensors work?

The functioning of ultrasonic distance sensors is very simple and can be related to the way bats fly. These devices send out ultrasonic pulses and then listen for returning echoes. These echoes are reflected off the target. Distance measurements are obtained from the time of transmission until the echo returns. Most distance sensors can also pick up targets that are small or even those which are very absorptive to sounds. Distance sensors are also capable of measuring multiple targets.

In certain instances, an independent measurement may be required for compensating the distance readings of distance sensors. This becomes necessary because the speed of sound in air differs with temperature. For this purpose, a simple calculation is used along with the initial reading and this helps to get a precise distance reading.

Like other sensors, there are different types of distance sensors and these are used for various applications. The most common applications in which distance sensors are used are measuring water levels and snow depths. Due to their applications, distance sensors have to be designed to meet the most stringent conditions.

Generally, pressure sensors fall into two different categories – non-contact and contact. Sensors that measure temperature have issues with their accuracy. However, it is important to recognise that the inconsistency estimates should be precise. You will also need to take many readings to get a final result with decent levels of precision.

Calibrating the temperature sensors is important, irrespective of whether it is a non-contact or contact temperature sensor. By calibrating the temperature sensors, you can greatly minimise the inconsistencies in the readings, thus making your measurements more accurate. This is a fundamental and important process prior to taking any measurements.

Contact temperature sensors measure their own temperature at any given point of time. This is usually done by creating a thermal equilibrium between the substance being measured and the sensor. In simple words, thermal equilibrium means there is no flow of heat between two bodies, thus both have the same temperature.

Contact sensors are standard for measuring temperature in science and industry. Thermometers and thermocouples are two types of contact sensors that are presently available. Basically, thermocouples utilise an electric current with a particular resistance level through which variations of the resistance can be used for measuring the temperature. This is termed the ‘Seebeck effect’. If you want to measure the temperature at any given point of time, non-contact or contact sensors may suit your requirements.