In this article we will discuss the most common and popular sensors used in Data Acquisition (DAQ) measurement applications today, with enough detail so that you will:

  • See what sensors are and what they do
  • Learn the basics of how each major sensor type works
  • Understand the importance of good sensors in industry and research

Are you ready to get started? Let’s go!

Sensors, also known as transducers, are one of the fundamental building blocks of modern data acquisition systems (AKA DAQ or DAS systems). These systems are comprised of the following basic components:

Data acquisition system schematicThe sensor is usually the beginning of a measurement chain in the modern data acquisition system

What Do the Sensors Do?

The easiest way to explain what a sensor is is to look at what a sensor does.

A sensor is a device that detects the change in the environment and responds to some output on the other system. A sensor converts a physical phenomenon into a measurable analog voltage (or sometimes a digital signal) converted into a human-readable display or transmitted for reading or further processing.

One of the best-known sensors is the microphone, which converts sound energy to an electrical signal that can be amplified, transmitted, recorded, and reproduced.

Sensors are used in our everyday lives. For example, the common mercury thermometer is a very old type of sensor used for measuring temperature. Using colored mercury in a closed tube, it relies on the fact that this chemical has a consistent and linear reaction to changes in temperature. 

By marking the tube with temperature values, we can look at the thermometer and see what the temperature is. The precision is somewhat limited due to the visual size of the scale markings, but it is sufficient for its intended purpose.

Thermometer sensor for measuring temperature

Of course, there is no output (other than the visual one). This kind of thermometer, while useful in the oven, or outside the kitchen window, is not particularly useful for data acquisition applications because, in order to record the values from it, we must have an output that can be digitized. So, temperature sensors have been invented to measure temperature and other physical phenomena and to provide an output that we can display, store and analyze. 

Let’s learn more about the most common and popular sensors in use today.

Types of Sensors

There are many types of sensorsThere are many types of sensors
Image source: Electronics Hub - link

There are many types of sensors that have been invented to measure physical phenomenon:

  • Thermocouples, RTDs and Thermistors: for measuring temperature
  • Strain gages: to measure strain on an object, e.g. pressure, tension, weight, etc.,
  • Load cells: for measuring weight and load
  • LVDT sensors: LVDTs are used to measure displacement in distance
  • Accelerometers: measuring vibration and shock
  • Microphones: for capturing sound waves
  • Current transducers: for measuring AC or DC current
  • Voltage transformers: for measuring high voltage potentials
  • Optical sensors: used to detect light, transmit data, and replace conventional sensors
  • Camera sensors: used to capture single and continuous 2D images
  • Digital sensors: used for discrete on/off counting, linear and rotary encoding, position measurements, etc.
  • Positioning sensors (GPS): used to capture the longitudinal, latitudinal position based on GPS, GLONASS, and other satellite positioning systems. Different GPS sensors with different accuracy are available.
  • and countless more.

Depending on the type of sensor, its electrical output can be a voltage, current, resistance, or another electrical attribute that varies over time. Some sensors are available with digital outputs, whereby they output a series of bytes of scaled or unscaled data. The output of these analog sensors is typically connected to the input of a signal conditioner, which we will discuss in the next section.

Next, we will take a brief look at each of the major sensor types in use today.

Check out Dewesoft's data acquisition systems that can connect any type and any number of sensors to record, store, analyze and visualize data.

Dewesoft DAQ Systems

Temperature Sensors

The most common and popular sensors for temperature measurement include:

  • thermocouples,
  • thermistors, 
  • RTDs,
  • and even infra-red temperature detectors.

Different type of temperature sensors - thermistor, thermocouple and RTDDifferent types of temperature sensors. From left to right: thermocouple, thermistors, and RTD.

Millions of these sensors are at work every day in all manner of applications, from the engine temperature shown on our automobile dashboard, to the temperatures measured in pharmaceutical manufacturing. Virtually every industry utilizes temperature measurement in some way.

Main Characteristics of Different Temperature Sensors

Sensor type Thermistor RTD Thermocouple
Temperature Range (typical) -100 to 325°C -200 to 650°C 200 to 1750°C
Accuracy (typical) 0.05 to 1.5°C 0.1 to 1°C 0.5 to 5°C
Long-term stability @ 100°C 0.2°C/year 0.05°C/year Variable
Linearity Exponential Fairly linear Non-linear
Power required Constant voltage or current Constant voltage or current Self-powered
Response time Fast
0.12 to 10s
Generally slow
1 to 50s
Fast
0.10 to 10s
Susceptibility to electrical noise Rarely susceptible
High resistance only
Rarely susceptible Susceptible / Cold junction compensation
Cost Low to moderate High Low

Thermocouples

The thermocouple is the most popular temperature sensor overall due to its relatively low cost and reliability. Thermocouples are based on the Seebeck effect, which demonstrates that when a pair of dissimilar metals in contact with each other at each end are subjected to changes in temperature, they create a small voltage potential.

Pairing different kinds of metals give us a variety of measuring ranges. These are called “types.” A very popular one is Type K, which pairs chromel and alumel, resulting in a wide measuring range of −200 °C to +1350 °C (−330 °F to +2460 °F). Other popular types are J, T, E, R, S, B, N and C.

Thermocouple types J, K, T, and E are also known as Base Metal Thermocouples. Types R, S, and B thermocouples are known as Noble Metal Thermocouples, which are used in high-temperature applications

The output from a thermocouple must be linearized by the measuring system.

It must also be referenced using the Cold Junction Compensation (CJC). The “hot junction” is the measuring end of the thermocouple assembly, and the other end is the cold junction, where the reference is typically located. Cold Junction Compensation removes the effect of the voltages generated by these cold junctions for more accurate temperature measurement.

Thermocouple Challenges

Due to the very small microvolt and millivolt output of these sensors, electrical noise and interference can occur when the measuring system is not isolated. Dewesoft modules tackle this head-on with powerful isolation. There is no better way to reject common-mode voltages that get into the signal chain.

Another way to reduce noise is to place the measuring system as close to the sensor as possible. Avoiding long signal lines is a proven strategy for maximizing signal fidelity and reducing costs. Look at our SIRIUS and KRYPTON modular instruments for best-in-breed solutions here.

An inadequate CJC results in wrong readings. This assembly needs to be protected from ambient temperature changes to provide a solid reference. We use a separate CJC chip for each channel in our CJCs, which are milled from a solid block of aluminum, and precisely assembled to achieve the best possible reference.

RTD Sensors

Compared to the thermocouple, the RTD (Resistance Temperature Detector) is generally more linear and drift-free within its measuring range. However, due to their platinum content and more complex construction, they are more expensive than thermocouples. 

You will typically find RTDs used in applications such as pharmaceuticals, where precise temperature measurements must be made over a long time. They don’t range much above 600° C, however, so thermocouples are a better choice for high temperature “contact” applications.

Unlike the thermocouple which is self-powered, the RTD must be powered by the measuring system. 

The RTD measures temperature via electrical resistance which changes in a highly linear fashion with respect to temperature. Although at its core an RTD is a 2-wire sensor, the addition of one or even two more wires (3 and 4-wire hookup) provides better compensation against self-heating and lead wire resistance and is recommended. Dewesoft signal conditioners provide 2, 3, and 4 wire hook-up possibilities.

Types of RTD Sensors

Pt100 (“PT” = platinum and “100” = 100Ω at 0°C) and Pt1000 are the most popular variants of the RTD sensors. There are, however, also other types such as Pt200, Pt500, and Pt2000 sensors. Dewesoft data acquisition systems support the connection and measurement of all types of RTD sensors.

As mentioned, RTD hook-up is more complex than a thermocouple, however, Dewesoft DSI-RTD adapters make it easy and convenient to connect your sensors to our measuring systems. Noise is always a consideration for any sensor with small output, but our high isolation inputs are the best prevention imaginable.

Another way to reduce noise is to place the measuring system as close to the sensor as possible. Avoiding long signal lines is a proven strategy for maximizing signal fidelity and reducing costs. Look at our SIRIUS and KRYPTON modular DAQ systems for best-in-breed solutions here.

Thermistors

A thermistor is a piece of semiconductor made of metal oxides that are pressed into a small bead, disk, wafer, or other shape and sintered at high temperatures. Lastly, they are coated with epoxy or glass.

When a current is passed through a thermistor, you can then read the voltage across the thermistor and determine its temperature. A typical thermistor has a resistance of 2000 Ω at 25ºC. 3.9 percent temperature coefficient.

Thermistors are inexpensive and have a fast response, but they are not linear, have a limited range, are relatively fragile unless mounted inside a probe for protection.

Pros and Cons of Different Temperature Sensors

  Pros Cons Best Application
Thermocouple
  • Wide measuring range
  • Self-powered
  • Simple to hook up
  • Rugged
  • Inexpensive
  • Non-Linear
  • CJC Reference Required
  • Not inherently isolated
  • Thousands of applications in factory, process and industrial temperature monitoring
  • Automotive environmental testing
  • Internal combustion and hybrid engine testing
  • Electrical motor and turbine testing
  • Medical, healthcare monitoring
  • Aerospace engine and control systems testing
RTD
  • Most Stable
  • Most Accurate
  • More Linear than thermocouple
  • Expensive
  • Current source required
  • Small ∆R
  • Low absolute resistance
  • Self-heating
  • Lead resistance error
  • Response time
  • Vibration resistance
  • Size
  • Pharmaceuticals, drug manufacturing
  • Food processing
  • Precise scientific measurements
Thermistor
  • High output level
  • Fast response
  • Easy installation
  • Very inexpensive
  • Output must be converted from change in resistance to a temperature reading
  • Limited range to ~ 200°C
  • Fragile
  • Electrical circuit monitoring
  • Automotive engine applications
  • Consumer electronics
  • Fire alarms
  • Thermostat control

Learn more about temperature measurement:

Dewesoft PRO Training -> Temperature Measurement

Strain Gage Sensors

When a strain gage (aka “strain gauge”) sensor is properly aligned and glued onto an object under test, and we apply stress to the object by bending or twisting it, the resistance of the strain gage will change linearly, and we can then measure it. We can also apply mathematics to calculate strain and other forces.

Typical single foil strain gage sensorTypical single foil strain gage sensor
Image source: courtesy of Cristian V. [CC BY 4.0 (https://creativecommons.org/licenses/ by/4.0)]

Strain Gage Applications

  • Strain and stress measurements
  • Weight and load measurements
  • Force measurement
  • Shock and vibration measurements

Strain Gage Advantages

  • Sensors themselves are inexpensive
  • Equally good at static and dynamic measurements
  • Useful across a broad range of applications

Strain Gage Disadvantages

  • Installation requires specialized knowledge
  • Signal conditioning required is relatively complex
  • Temperature can affect measurements

Load Cell Sensors

If we take another step and permanently affix four strain gage sensors to a body of a given shape, we create a different sensor called a Load Cell. This is essentially a force or pressure sensor.

The most well-known load cells are the ones installed at the bottom of your digital bathroom scale. When you step onto the scale and compress the load cells, they output a change in resistance, which a microcontroller measures and converts into a value in kg (lbs).

A “bar” or “bending beam” (aka “binocular beam”) load cell is commonly used for industrial weighing applications. One end of the bar is fixed to a structure, while a force is applied to the free end of the sensor (see F in the graphic below). 

This force causes the four strain gauges that are built into top and bottom and each end of the load cell to elongate or compress depending on how much application or removal of the force stresses the load cell structure. These tiny changes in potential from the strain gages are easily converted to weight within our DAQ system.

Typical bending beam load cellTypical Bending Beam Load Cell
Daraceleste [CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)]

Load cells are available in many shapes and sizes: some for very tiny spaces and small loads, and others for huge loads of hundreds of thousands of tons, etc. 

Load Cell Applications

  • Materials testing - weighing parts as they are manufactured for consistency
  • Aerospace - jet engine thrust, load on wheels and undercarriages
  • Marine - mooring line tensions
  • Transportation - torque measurements on engines, highway truck weigh stations
  • Industrial -  tension and force measurements in paper and metals mills
  • Medical / Healthcare - Infant incubator scales, physical therapy equipment.
  • Construction - Cable forces in elevators, forces on scaffolding 
  • Entertainment - cable tension tests on cables used to hoist acrobats
  • Petrochemical - measuring the forces on oil and gas drilling tools
  • Farming and Ranching - weighing livestock, hopper, tankard and silo weighing
  • Household / Consumer - digital bathroom scales, kitchen food scales

Load Cell Advantages

  • Accurate and repeatable measurements
  • Available from very small loads to hundreds of thousands of kg/pounds
  • Available in a variety of shapes and sizes for numerous applications

Load Cell Disadvantages

  • Measurements can be affected by ambient temperature
  • Require relatively expensive strain gage signal conditioning

Learn more about load cells and weight measurement:

How to Measure Weight using Load Cell Sensors

LVDT Sensors

LVDT (linear variable differential transformer) transducers are used to measure linear displacement/position over relatively short distances. They consist of a tube that contains a rod. The base of the tube is mounted to a fixed position, and the end of the rod is affixed to something that moves.

Cross-section of a typical LVDT sensorCross-section of a typical LVDT sensor
Image Source: Wikimedia Commons

As the rod is pulled out from the tube or slides back in, the sensor outputs a signal that represents the position of the rod from its starting point to its maximum deflection. The rod does not touch the inside of the tube, making it virtually frictionless, and the LVDT itself contains no electronics, making it popular in harsh environments.

LVDT Applications

  • Thousands of Industrial, factory and process measurement applications
  • Aerospace - actuator and control surface test
  • Transportation - monitoring ride height between truck and train body
  • Petrochemical - positioning of drilling tools

LVDT Pros

  • Highly accurate and repeatable measurements
  • Long lifespan due to virtually frictionless operation
  • Available from very micrometers to ~ 0.7 m (27 in.)
  • Absolute output (after power restoration the reading returns to correct value)
  • Available in a variety of types and sizes for different applications

LVDT Cons

  • Measurements can be affected by ambient temperature
  • Require AC excitation 

Vibration Sensors - Accelerometers

Accelerometers are used for measuring vibration and shock on machines and basically anything that moves. Their outputs can also be integrated and double-integrated to calculate displacement and velocity.

Accelerometers for making dynamic measurements are normally based on the piezoelectric principle: when a  quartz crystal is put under stress it releases a stream of charged ions proportional to the stress. These charge sensors are connected to a charge type signal conditioner. An even more popular type is IEPE (aka ICP®) sensors, which have an integrated preamplifier, and which require a less expensive signal conditioner. 

Two accelerometers and modal hammer connected to Dewesoft DAQ systemTwo accelerometers and modal hammer connected to Dewesoft DAQ system 

There are also capacitive type accelerometers that are based on a different principle, and which are popular in less demanding industrial applications.

Additionally, there are MEMS-based accelerometers that are heavily used in navigation applications, tablet, and phone orientation, automotive testing, and motion capture.

Accelerometer Applications

  • Shock and vibration tests of all kinds, across all industries
  • Aerospace - fuselage strain and stress tests, jet and rocket engine vibration test
  • Transportation - Recording shock and vibration during transporting fragile items
  • Automotive - body panel shock and vibration, passenger comfort tests, engine vibration
  • Human body vibration tests
  • Torsional and rotational vibration tests

Accelerometer Advantages

  • Easy connection
  • Models available for dynamic and dynamic and static measurements
  • Available in a variety of types and sizes for different applications
  • Charge sensors require no external power
  • IEPE sensors allow longer cable and less expensive cables and signal conditioning

Accelerometer Disadvantages

  • Sensors can be damaged by too much shock
  • Charge sensors require signal conditioning that is more expensive than IEPE sensor signal conditioning
  • Mounting of sensors requires some specialized knowledge

Sound Sensors - Microphones

In addition to being used in the entertainment industry, microphones are also manufactured to be used in data acquisition applications for analyzing and measuring sound and noise. 

Typical sound measuring microphone from GRAS instrumentsTypical sound measuring microphone
Image courtesy of GRAS Instruments

Microphones are used in noise and vibration studies, human hearing studies, automotive pass-by noise applications, and thousands more. 

Microphone Applications

  • Noise and vibration tests of all kinds, across all industries
  • Aerospace - Jet engine noise testing
  • Transportation - Recording shock and vibration during transporting fragile items
  • Automotive - engine noise, pass-by noise test, brake noise tests
  • Medical - ambient noise impact studies, hearing testing

Microphone Advantages

  • Easy connection - readily available 50Ω BNC cables are used
  • Available in a variety of types for different applications
  • Easy to install

Microphone Disadvantages

  • Relatively expensive sensor
  • Can be damaged if dropped or mishandled
  • Some mics require phantom power from the signal conditioner

Current Transducers

Along with voltage, a current is one of the most fundamental forms of energy that we measure for monitoring and analytical purposes. Whether it’s testing the quality of the energy of the power grid, or the energy consumption of a hybrid electric automobile, or a machine, power is critically important.

For small to medium levels of current, we can use current shunts to convert current to voltage. A shunt is basically a resistor that is installed directly into the circuit where we want to measure the current.

Most of the other kinds of current sensors and transducers on the market operate via induction or a related method whereby they are NOT part of the circuit. This allows much higher currents to be measured. Shown below, a typical current clamp - a device that detects the electromagnetic field created by a current and measures it. The sensor output is a proportional voltage that our DAQ system can display, store, and later analyze.

There are flexible Rogowsky coils that are easy to install even in places where it is difficult to reach, or when disconnecting the circuit is undesirable. There are also zero flux and fluxgate current sensors for high accuracy applications, especially those in power quality and related fields. There is a broad range of current sensors and transducers, specifically engineered for all kinds of applications.

Current transducers from DewesoftCurrent clamps from Dewesoft

Current Transducer Applications

  • Energy Production and Distribution tests of all kinds, power quality tests, fossil fuel, and nuclear power plant monitoring
  • Aerospace - engine and power system testing
  • Automotive - electrical system test, hybrid, and electric motor tests
  • Transportation - electric subway cars, third rail and pantograph tests, electrical energy distribution centers

Current Transducer Advantages

  • Clamp models easy to attach to AC cables
  • FLEX Rogowski models easy to connect around hard-to-reach places
  • Passive and powered clamps for AC applications
  • Long-life operation

Current Transducer Disadvantages

  • Relatively expensive sensor
  • DC clamps, Rogowsky and Flux sensors require external power

Voltage Transformers - Potential Transformers

Along with current, voltage is one of the most fundamental forms of energy that we measure for monitoring and analytical purposes. Whether it’s testing the quality of the energy of the power grid, or the energy consumption of a hybrid electric automobile, or a machine, power is critically important.

Nearly every DAQ system and data logger in the world can directly accept low and medium voltages in the ranges of 0-10V or 0-50V, so we do not need any transducer to reduce this voltage. From 50V to approximately 1000V there are signal conditioners available for DAQ systems such as the SIRIUS-HV module, which can directly and safely accept these voltages and internally step them down so that they can be digitized, displayed and stored.

But at higher voltages, or in any case, when life-threatening currents and voltages are present, it is essential to use a high voltage transformer to step down the high voltage and isolate the human test operator from dangerous voltage and current. Such a device is called either a Voltage Transformer (VT) or a Potential Transformer (PT).

Typical Potential TransformerTypical Potential Transformer

The typical PT uses a transformer to step down a very high potential - even higher than 10kV - down to a safe level. It can be placed in series with or across the circuit being monitored. The transformer’s primary winding has a large number of turns compared to the secondary. 

Because the DAQ system connected typically has a very high impedance, a very little current will flow, therefore the PT’s secondary winding experiences almost no load at all. Most PTs output between 50 and 200V, which nearly every DAQ system can accept.

PTs are available for outdoor usage and those designed for indoor usage. There are also those designed for electrical metering applications. There is also an alternative to the pure transformer type which uses a bank of capacitors after an intermediate transformer to further step down the voltage. These can be less costly because the relatively low step-down ratio intermediate transformer is less expensive than the conventional wound transformer with a high step-down ratio. 

A third variant is the optical VT. Optical VTs are usually found in power substations, and not often in DAQ applications. Since they operate on the principle of the Faraday effect, whereby the polarization of light is affected directly by a magnetic field, they are inherently isolated. They are also extremely accurate.

ABB outdoor voltage transformer
Outdoor 36 and 200 kV outdoor voltage transformer
Photo courtesy of ABB 
https://bit.ly/2uO97xa 

Voltage Transformers Applications

  • Energy Production and Distribution high voltage power line testing, synchronizing generators with the main power grid, 
  • Aerospace - engine and power system testing
  • Automotive - electrical system test, hybrid, and electric motor tests
  • Transportation - electric subway cars, third rail and pantograph tests, electrical energy distribution centers

Voltage Transformers Advantages

  • They provide essential safety to the test engineer and technician
  • Easy to use
  • Most models do not require external power
  • Long-life operation

Voltage Transformers Disadvantages

  • Can be expensive

Optical Sensors

There are several applications for optics within the sensor market today:

  • Sensing light, IR and UV
  • Detecting Object Distance, Absence/Presence
  • Replacement of Conventional Sensors

Sensing Light, IR, and UV

There are countless applications for detecting or measuring how much ambient light is around the sensor. The most obvious examples include automatic switches for turning off or on lights: this requires a photodetector.

Even our mobile phones have a light sensor so that they can automatically adjust screen brightness. Most cars today turn on their headlamps automatically when daylight ends, and even turn on/off high-beams at night when an approaching vehicle is detected. Automatic cameras measure the ambient light in order to set the exposure correctly.

The main technologies used for the applications listed above (and more) include photovoltaics, photocells aka photoresistors. They are designed to detect and measure light

And although most of these sensors are designed for the human visible spectrum, some are designed to work within the infrared (IR) spectrum and even the ultraviolet (UV) spectrum. The IR spectrum is what many robotic systems use, as well as our television remote controls at home. IR radiation cannot be seen by the human eye, but it can be damaging to our eyes in high doses, so detecting it is important for safety purposes among many other applications.

Typical photocell sensor

Typical photocell
By Levan jgarkava - own work, Public Domain,
https://commons.wikimedia.org/w/index.php?curid=7726138 

A photocell, also called a photoresistor or LDR (light dependent resistor) can detect the presence and amount of light because of its output changes in proportion with how much light falls on the cell, which has a pattern on it usually made from cadmium sulfide. When no light shines on the cell, its resistance is extremely high. But when light hits the cell its resistance drops in proportion with the amount of light.

Paired with the appropriate signal conditioning, it can be used as an on/off sensor, or to measure the intensity of light. Based on the chemistry of the cell, these small and inexpensive cells can detect all the way into the infrared spectrum.

Detecting Object Distance, Absence/Presence

Photodetectors aka proximity sensors, as well as their semiconductor-based cousin, the photodiode, are used to measure the distance to or between objects, and also to sense either the presence or absence of an object.

These are used in a wide variety of industrial applications, including factory process lines, making sure that objects are spaced properly on a belt, or to detect when a new object is in position on an assembly belt. They are also used in automotive applications, detecting the presence of another car or object, as well as alarm systems, and CD and DVD drives.

Typical photodetectorTypical photodetector from a CD drive
Jacopo Werther / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Replacement of Conventional Sensors

The next level is to use optics to do the sensing itself, both augmenting and replacing conventional technology sensors like strain gauges, accelerometers, temperature sensors, and more. More about this new trend will be added to this article in the near future, so please check back.

Fiber Optic Transmission

In addition to sensor performance, another advantage is the fiber optic transmission of the sensor data itself compared to using copper cables.

 

Fiber Optic cable construction
Fiber Optic cable construction
Photo source: https://upload.wikimedia.org/wikipedia/commons/f/f0/Fiber-optic-construction.png

Today, fiber optics are being used instead of electrical transmission to send signals from one point to another. We see this even in our own homes, where fiber is used to bring television and the internet to our homes at transmission speeds that are higher than conventional cable. Fiber optical transmission also provides several distinct advantages over electrical transmission, including:

  • Immune to magnetic interference
  • Immune to resistance and heating
  • Very long signal transmission path without signal loss
  • Multiple signal wires can be reduced to a single thin cable
  • Very high bandwidth

Optical Sensor Applications

  • Turning on/off lights automatically, alarm systems
  • Factory process applications, assembly lines, conveyor systems
  • Robotics, movement direction, and detection
  • Smoke detectors
  • Medical sample analysis
  • Laser range finders, night vision goggles
  • Automatic door openers

Optical Sensor Pros

  • Fiber Optic transmission is a very high speed and not susceptible to interference from electromagnetic interference and other external forces
  • Optical sensors are non-contact and thus long-lived
  • Most optical sensors are inexpensive and quite small

Optical Sensor Cons

  • Photocells (aka photoresistors) are relatively slow to react to light changes

Camera Sensors

We think of cameras as something only used to take pictures or movies, but they are heavily used in all kinds of industrial and scientific applications as well. Factories use single and continuous image sensor cameras (aka video cameras) to monitor and control a wide variety of fabrication and assembly line processes.

Industrial high-speed video camera from DewesoftIndustrial high-speed DS-CAM video camera from Dewesoft

Cameras are also an important part of DAQ system measurement applications. In fact, all of the DAQ systems made by Dewesoft can utilize one or more video cameras and record video in sync with the analog and digital data that they’re recording.

Screenshot from a Dewesoft DAQ system showing analog and digital data synchronized with video https://youtu.be/RwSPUk7yK9U 

Professional vs. Consumer Cameras

On one end of the capabilities spectrum, it is possible to use a very inexpensive web camera to add a video to your recordings in some DAQ systems. But on the other end are industrial grade cameras with better lenses and the ability to synchronize the framerate of the camera to the process being recorded and/or with the data acquisition sample rate. 

For example, the DS-CAM-600 shown here can output up to 336 frames per second at full HD resolution, and up to 600 frames per second if the size of the image is reduced. The camera is also sealed to IP 67 so that it can be used in wet, dusty and harsh environments. Within Dewesoft DAQ systems, multiple cameras can be used at the same time, providing different viewing angles of the object(s) under test. 

When Dewesoft added the common webcam to its DAQ systems in the early 2000s, it completely revolutionized the DAQ market. The next logical step was using industrial cameras whose frame rates could be precisely controlled, and which offered better resolution and speed. 

Mechanical mounting and rugged construction are also critical with any sensor, and this has been designed into today’s best industrial machine vision cameras.

Infrared or Thermal Cameras

Infrared cameras are also sometimes used in scientific and industrial applications and are another important sensor for DAQ applications. Infrared cameras can “see” the temperatures within its field of view, so it’s the perfect way to measure temperature without making any contact.

Data file export from the Dewesoft X using synchronized analog data, IR and standard cameras

Infrared is extremely useful in troubleshooting in power plants because power supplies and generators that are hotter than normal indicate a problem. With one look using an IR camera is it easy to see trouble spots.

The same is true with automotive brake testing, where IR cameras make it possible to measure the precise temperature of the brakes in operation and measure accurately how fast they heat up and cool down under a variety of conditions. They are being used more and more in ADAS (advanced driver assistance systems), as they allow the car to detect people and other sources of thermal energy before they come into view, especially at night.

Being able to “see” in a completely different spectrum opens up many possibilities in virtually every test and measurement application today. The best-known maker of IR cameras is FLIR, and Dewesoft has integrated many of their cameras seamlessly into their DAQ systems so that continuous thermographic data can be acquired in sync with the analog and digital sensor data, as shown in the example above.

High-speed Cameras

High-speed cameras are useful for capturing extremely fast-changing events. You’ve probably seen slow-motion replays of a balloon popping, or a bullet impacting glass of water - those videos were captured with high-speed video cameras. 

Photron high speed camerasAn assortment of high-speed video cameras from Photron

High-speed cameras from Photron capture up to 500,000 pictures per second. This data is captured to RAM and then is immediately available for replay. It is possible to synchronize Dewesoft DAQ systems with Photron cameras so that they are both triggered at the same time, and when the test is over, the high-speed video is immediately transferred to the Dewesoft DAQ system and automatically synchronized with the other data. You can replay it in perfect sync with all the data from other sensors.

Video from a fuse switch test using Dewesoft DAQ equipment and software

Summary

Cameras provide a unique context to the data that engineers record, adding a vital layer of information and understanding to countless research and testing applications.

Camera Sensor Applications

  • Industrial cameras:  Factory automation and process control; automotive pass-by noise tests, wind tunnel tests, brake tests; aerospace control surface tests, escape slide tests, engine tests
  • InfraRed cameras: energy and power tests, automotive ADAS (advanced driver assistance systems)
  • High-speed cameras: Ballistics testing; fluid dynamics research; materials testing; automotive crash testing; aerospace wind tunnel testing

Camera Sensor Advantages

  • Industrial cameras:  IP67 environmental protection; synchronized output; frame rates up to 600 fps; direct comparison of sensor data with images of the object(s) under test; exchangeable lenses
  • InfraRed cameras: Contactless temperature measurement; direct comparison of sensor data with thermal imagery in real-time
  • High-speed cameras: Capturing rates up to 500,000 frames per second

Camera Sensor Disadvantages

  • Industrial cameras: More expensive than webcams 
  • InfraRed cameras: Expensive; IR cannot “see” through glass
  • High-speed cameras: Very expensive; short recording duration due to high sample rates; require either a lot of ambient light on the subject or a DC light

Digital Sensors

When we talk about digital sensors, we refer to those sensors that output discrete values, usually related to the linear or angular position, as well as those sensors that are used to detect when an object is nearby. Let’s take a look at the most commonly used digital sensors.

Proximity Sensors

A proximity sensor is able to detect a nearby object without making contact with it, and then output a pulse or voltage signal. There are several types of proximity sensors, which are chosen based on the composition of the object(s) that should be detected. 

Typical proximity sensorTypical proximity sensor

Rotary Encoders

A rotary encoder typically provides excellent angle resolution, as they are available with up to thousands of steps per 360° revolution, which allows for steps far smaller than 1°. Many encoders can also detect the direction of rotation, which is essential in some applications.

Typical rotary encoder
Typical Rotary Encoder

Incremental Encoders

Incremental encoders report relative changes in position and direction - they do not track absolute position (angle). 

Incremental encoders output A and B signals, which indicate changes in movement and direction. Some of them are capable of being “homed” or referenced to a particular position. When this position is reached an additional Z output signal is generated. Incremental encoders are the most common and popular types of encoders.

Linear Encoders

A linear encoder measures position along a linear path. Unlike a rotary encoder which has a circular plate inside that allows it to measure shaft position, most linear encoders move along an external scale and determine their position from markings on the scale.

Typical linear encoderLinear Encoder
Image courtesy of Heidenhain

A perfect example is an inkjet printer, which uses a linear encoder to precisely move the printhead back and forth along a scale during printing. High resolution and accuracy are obviously required in this and countless other applications.

The most prevalent sensing technology used with linear encoders is optical, however, there are encoders that also employ magnetic, capacitive and inductive technology. Optical encoders provide the most accuracy and the highest possible resolution, however, care must be taken to prevent contaminants from interfering with their operation.

There are both analog and digital output linear encoders. Dewesoft systems are better suited to digital outputs since they provide A and B outputs very similar to incremental rotary encoders as described in the previous section.

Gear Tooth Sensors

This angle-based sensor consists of gear with teeth around its circumference plus a proximity sensor of some kind positioned so that when the teeth pass by, they will be detected. This proximity sensor is typically a Hall Effect type, but others are possible. The gear needs to be mounted onto the rotating shaft that we want to monitor.

Gear tooth with proximity sensorGear tooth with proximity sensor

The Hall effect proximity sensor detects the variation in flux found in the air gap between a magnet and passing ferrous gear teeth. In modern systems, the signal is converted into a binary square wave that is immune to orientation requirements and can follow the gear speed down to a full stop … and detect the first gear tooth that passes immediately upon power on.

Most Hall Effect sensors can detect not only gear teeth passing by, but can also be used to detect holes in disks and plates, ferrous features (e.g., bolts) added to a wide variety of disks and plates, notches in drive shafts and camshafts.

Digital Sensor Applications

  • Proximity sensors: Counting RPM of rotating shaft (tachometer applications); Counting parts passing through production line; Intersection vehicle detection (buried in the road)
  • Rotary encoders: Speed measurement of motors, conveyors, filling systems, pick and place systems; machine speed, position and distance measurements (textiles, pulp & paper, metals manufacturing)
  • Linear encoders: CNC machines; Inkjet printers; laser scanners; pick-and-place manufacturing systems; robotics
  • Gear Tooth Sensors: Measuring RPM of rotating shafts; engine combustion analysis; torsional and rotational vibration studies

Digital Sensor Advantages

  • Proximity sensors: Very reliable; low cost; capacitive types can also be used to measure thickness; inductive types are not affected by water, mud, etc.
  • Rotary encoders: High speed/low latency; high resolution; highly reliable and accurate
  • Linear encoders: Same as with rotary encoders
  • Gear Tooth sensors: Typically very rugged and hard to break; very low initial and operating cost

Digital Sensor Disadvantages

  • Proximity sensors: Limited detection distances (~70mm); require external power
  • Rotary encoders: RF and EM interference possible with magnetic encoders; light interference possible with optical encoders
  • Linear encoders: Same as with rotary encoders
  • Gear Tooth sensors: Limited detection distances; limited angle resolution compared to encoders, which can provide hundreds or thousands of steps around the 360° rotation of a shaft.

Summary

We hope that you gained a better understanding of what sensors are, how they work, and how they can be applied across a truly mind-boggling range of monitoring and testing applications. Sensor technology is always moving forward, making these sensors better and better, and finding even more efficient ways of making accurate and repeatable measurements. Sensor-based technology itself is constantly evolving. 

Admittedly this article has only scratched the surface. There are many more sensors available today, including ultrasonic sensors that use reflected ultrasonic waves to measure distance, chemical sensors for detecting gases and vapors, and so many more. 

Detailed Information About Various Sensors

Specific details about each major kind of sensor are given in these articles:

Sensor Type Article Link
Strain Gages Measuring Strain and Pressure with Strain Gages
Load Cells Measuring Weight with Load Cells
Accelerometers Measuring Shock and Vibration with Accelerometers
Thermocouples **COMING SOON** Measuring Temperature with Thermocouple Sensors
RTDs **COMING SOON** Measuring Temperature with RTD Sensors
Thermistors **COMING SOON** Measuring Temperature with Thermistor Sensors
Voltage Transducers **COMING SOON** Measuring High Voltages with Voltage Transducers
Current Sensors **COMING SOON** Measuring Amperes with Current Sensors
LVDTs **COMING SOON** Measuring Distance with LVDT Sensors
Encoders Measuring RPM, Angle, and Speed with Counter and Encoders Sensors

List of Major Sensor Suppliers By Sensor Type

COMING SOON: See the article List of Sensor Companies By Type.

Check out Dewesoft's data acquisition systems that can connect any type and any number of sensors to record, store, analyze, and visualize data.

Dewesoft DAQ Systems