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What Is a Silicon Carbide (SiC) MOSFET?

SiC MOSFET is a MOSFET that uses a silicon carbide (SiC) MOSFET, a compound semiconductor, instead of the conventional Si substrate.

MOSFETs are used for on/off switching, amplifiers, and other applications. By using SiC, a compound semiconductor, as the semiconductor substrate material, it is possible to reduce the resistance when voltage is applied compared to a conventional silicon carbide (SiC) MOSFET.

As a result, switching loss during turn-off,and power loss during power operation can be reduced. This can improve the performance of the semiconductor chip and reduce the cooling capacity required during transistor operation, leading to downsizing of the product itself.

Uses of Silicon Carbide (SiC) MOSFETs

SiC MOSFETs are used in many semiconductor products, such as relays, switching power supplies, and image sensors in the field of power electronics. SiC MOSFETs are also used in communication equipment in many cases.

When selecting a silicon carbide (SiC) MOSFET, the operating conditions of the product application must be considered, i.e., absolute maximum ratings, electrical characteristics, package use and size, etc.

Principle of the Silicon Carbide (SiC) MOSFETs

Silicon carbide (SiC) MOSFETs can achieve a MOSFET structure that allows low ON resistance and low-loss operation during turnoff, while maintaining a similar level of withstand voltage. This is because the active layer thickness can be reduced because the transistor is made of SiC substrate, which has properties of band gap energy about 3 times higher and breakdown field strength about 10 times higher than that of Si substrate.

A silicon carbide (SiC) MOSFET has a stacked structure of p-type and n-type semiconductors. Usually, the n-type semiconductor is stacked on top of the p-type semiconductor. The drain and source electrodes are attached to the n-type semiconductor, and the oxide insulating layer and gate electrodes are attached between the n-type semiconductors. In addition, SiC (silicon carbide), a compound semiconductor, is used as an epi-substrate for the silicon wafer of the body.

In a MOSFET, applying a positive voltage to the gate causes a current to flow between the source and drain. In this case, a silicon carbide (SiC) MOSFET, which uses SiC in the silicon wafer, can operate with a larger voltage and current between the source and drain than a MOSFET that uses only Si. Since the concentration of impurities in the semiconductor can be increased, losses can be reduced and the size of the MOSFET can be made smaller.

Other Information on Silicon Carbide(SiC) MOSFETs

1. Distinction Between Silicon Carbide (SiC) MOSFETs and IGBTs

IGBTs are transistors used for applications in the high-power range, which are difficult to handle with ordinary Si MOSFETs, but recently SiC MOSFET devices are being used in this range. SiC MOSFET devices are being used in this area because SiC has a large band gap energy, which allows it to operate at higher temperatures than IGBTs. Another reason is that SiC MOSFETs can overcome the problem of large switching losses in the subsequent bipolar transistor in the case of IGBTs.

In the past, SiC epi-substrates had a small diameter, making mass production and cost difficult. Recently, however, it has become possible to use 8-inch substrates, and mass production and prices have been improving.

SiC is being actively used in relatively large power handling applications exceeding 10 kW, such as electric vehicle (EV) applications, power generation system applications, and residential power applications.

2. Differences Between SiC and GaN Devices

Along with SiC, gallium nitride (GaN) is another wide band gap semiconductor that is attracting attention. GaN has a larger band gap energy and higher dielectric breakdown strength than SiC, and is the subject of active research at research institutes.

Since GaN generally consists of a GaN active layer on a Si substrate, it is difficult to support high-power applications as well as SiC MOSFETs. In the market, applications that handle power equivalent to 1KW are relatively being considered. Examples include high power amplifier applications for 5G base stations and battery charging applications via PC or USB.

GaN devices, like silicon carbide (SiC) MOSFETs, can operate at high temperatures and do not require cooling equipment or excessive heat removal structures, which has led to their widespread use in recent years as compact PC power adapters.

What Is a Circuit Breaker Switch?

A circuit breaker switch is an electrical device that enables or disables the flow of power by opening or closing its contact points, functioning as a critical component in controlling and protecting electrical circuits. Commonly known as switches, these devices vary, with electromagnetic circuit breakers/contactors being standard in low-voltage scenarios. Thermal relays add functionality, differentiating electromagnetic switches from contactors.

Uses of Circuit Breaker Switches

Employed extensively in industrial settings, circuit breaker switches have diverse applications including:

• Driving motors for pumps and fans
• Controlling electric heaters
• Managing main power supplies for industrial equipment
• Powering commercial facilities with high-voltage

Protection against short circuits and overcurrent, especially in motor drives, is often managed with thermal relays and breakers to ensure safety and equipment integrity.

Principle of Circuit Breaker Switches

Electromagnetic contactors serve as a prime example, comprising terminals, contacts, an iron core with an electromagnetic coil, and a casing. Additional thermal relays define an electromagnetic switch, enhancing its functionality and application range.

1. Terminal

Connection points for wiring, which vary by region and application, ensuring secure electrical connections.

2. Contacts

The conductive parts that allow electricity to flow, designed to handle varying currents with materials like silver alloys for low resistance and gold for sensitive applications.

3. Iron Core and Electromagnetic Coil

These components magnetize when energized, driving the contacts to connect or disconnect the electrical circuit, with designs ensuring reliable operation through mechanical or magnetic latching.

4. Casing

Protects internal components while providing insulation, with modern designs allowing for easy mounting and robust protection.

Types of Circuit Breaker Switches

Circuit breaker switches come in various forms, including:

1. Electromagnetic Circuit Breaker Switch

Utilizes electromagnetic force for operation, suitable for low-voltage applications.

2. Push Button Station

A manually operated switch, holding its state until reset, used without thermal relays but crucial in direct control applications.

3. Airborne Category Switchgear

Designed for high-voltage circuits, these switches manage load disconnection and are often paired with protective devices to ensure comprehensive circuit protection.

What Is a Digital-To-Analog Converter?

A digital-to-analog converter is an electronic circuit that transforms digital signals into analog signals, bridging digital devices and the analog world. As digital devices like PCs and smartphones operate on digital signals, a digital-to-analog converter is essential when analog output, such as sound or light, is required. Due to the continuous nature of analog signals, the digital-to-analog converter output is an approximation of the digital input. An AD converter performs the inverse operation, converting analog signals to digital.

Uses of Digital-To-Analog Converters

Digital-to-analog converters are integral to devices requiring analog signal output, including PCs, smartphones, digital audio devices, and TVs. They also play a critical role in smart speakers with speech synthesis functions, converting digital audio data into analog signals. External digital-to-analog converters, offering high-quality audio output, have become popular for enhancing sound quality from digital sources. Moreover, digital-to-analog converters are used in video equipment for converting digital video data into analog signals for devices with VGA and RCA inputs. Industrial equipment also relies on digital-to-analog converters for precise, continuous control.

Principle of Digital-To-Analog Converters

The resistor-string method is a common, cost-effective digital-to-analog converter conversion technique, utilizing a series of resistors to create voltage levels proportional to the digital input. This method offers linear and accurate conversions but scales poorly with increased resolution. Alternative methods include capacitor-based, current source, and low-pass filter approaches for varying applications and performance needs.

Other Information on Digital-To-Analog Converters

1. Cautions When Using Digital-To-Analog Converters

Despite improvements in digital-to-analog converter conversion accuracy, the discrete nature of its output can introduce noise, affecting the analog signal quality. The performance of connected components, such as speakers, also influences the final analog output quality. Adjustments and component selections should be made with the system’s overall balance in mind.

2. Accuracy of Digital-To-Analog Converters

As digital-to-analog converters find applications in increasingly sophisticated systems, their precision becomes critical. Digital-to-analog converter accuracy is affected by offset error, gain error, and integral non-linearity error, with the total error being a combination of these factors. While offset and gain errors can be calibrated, integral non-linearity errors are more complex, necessitating memory for error parameters and careful management to minimize system load.

What Is an ADC?

An ADC is a device that converts analog data into digital data.

Most information in the real world is continuous analog data, which must be converted into digital data expressed in terms of 0s and 1s to be processed by a computer. The opposite is called an ADC, which converts digital data to analog data.

ADC is available in various architectures (conversion methods) with different sampling rates and resolutions. Therefore, it is necessary to select the appropriate one according to the purpose.

Uses of ADCs

ADCs are used in numerous applications in our daily lives. Specifically, they are used in digital cameras and audio equipment. They convert analog data such as video and sound into digital data for output.

Various electronic devices need to use analog signals as input information, but the internal processing is done with digital signals. Therefore, ADCs are required. ADCs are installed in devices that handle light, temperature, etc.

High-speed ADCs with high sampling rates are being developed for digital cameras and audio equipment, which require high-speed transmission.

Principle of ADCs

The conversion of analog data into digital data by ADCs is divided into three major stages.

1. Sampling is performed by periodically cutting out a continuous analog signal.
2. Approximating the amplitude of the sampled signal to a discrete value is done.
3. Encoding is performed to represent the approximated signal in binary 0s and 1s. The circuit that performs the encoding is called an encoder.

Sampling rate and resolution are indicators of ADC performance. The sampling rate represents the speed of conversion; the higher the value, the faster the conversion.

Resolution is an indicator of how finely the data can be expressed and is expressed in bits (the number of binary digits in the encoding). The higher the value, the smoother and more accurate the representation.

There is a trade-off between sampling rate and resolution, whereby resolution is sacrificed for high-speed sampling, while a slower sampling rate is required to achieve high resolution.

Other Information on ADCs

1. Resolution of ADCs

The resolution of ADCs are concept of how finely the input analog signal can be quantified. The unit is expressed in bits, where 8-bit data is broken down to the eighth power of 2 and expressed as a number from 0 to 255. In general, the number of bits is often a multiple of 8.

If the analog input is a number from 0 to 2 and the ADCs have an 8-bit resolution, then 2/(2^8-1) = 2/255 = 0.007843. From the above, the minimum resolving power of an 8-bit-ADCs that can input from 0 to 2 is 0.007843. As high-precision ADCs, 32-bit, and 64-bit products are in practical use. 

2. Sampling rate of ADCs

In ADCs, the sampling rate is an important index as well as resolution; the sampling rate of ADCs is how often it samples an analog quantity. This is the speed at which the Analog-to-Digital converters operate.

By the Nyquist Theorem, we know that ADCs require a frequency that is at least twice the frequency of the input analog signal. Therefore, the sampling rate of the ADCs is set to 2.2 times or more than the input analog signal frequency. 

3. Accuracy of ADCs

ADCs are subject to errors. For example, a 16-bit ADCs with an analog input of 0 to 2 has an error of 2/(2^16-1)=0.0000030518. The degree of accuracy at which sampling is required is determined by the above calculation.

It is important to note that the performance of the ADCs does not always directly translate into the performance of the device; input protection circuits, amplifiers, attenuators, etc. are provided before the input terminals of the ADCs, where minute signals are handled.

If the peripheral circuits of the ADCs are not carefully selected, the performance of high-precision ADCs may not be fully demonstrated.

What Is a Flow Sensor?

A flow sensor is a measuring instrument that measures the flow rate of a fluid, from gas to liquid.

It is sometimes treated as a flowmeter. Flow rate is the volume or weight of fluid that passes through one cross-section in a unit of time.

There are various types of flow sensors, including analog flow sensors that monitor the fluid flowing in a fluid circuit for abnormalities, and digital flow sensors that are connected to a feedback control mechanism to adjust the gas supply to a certain volume.

Uses of Flow Sensors

Flow sensors are used in the following fields:

1. Hydraulics, Pharmaceutical/Chemical, and Food Industries

Flow sensors are mainly used to control the input of raw materials in manufacturing processes. The volumetric flow sensor is used in these fields.

2. Measurement of Industrial Gases, Fuel Gases, and Exhaust Gases

Flow sensors are used to control the amount of industrial gases, fuel gases, and exhaust gases used in factories. Thermal mass flow meters are the most common type.

3. Drinking Water, Sauces, and Flammable/Explosive Fluids

Food-related and highly hazardous fluids require non-contact measurement that does not touch the fluid For this purpose, electromagnetic flow sensors are used.

4. Industrial Facilities and Water Treatment Facilities

Flow sensors are used for flow control in industrial plants and water treatment facilities. Ultrasonic flow sensors are used especially when adding flow sensors to existing pathways.

5. LNG Plants, Automotive, Chemical, and Pharmaceutical Industries

Flow sensors are used in a variety of manufacturing settings. Coriolis flow sensors are most commonly used.

6. Chemical and Pharmaceutical Industries

Kalman vortex flow sensors are widely used in plants that handle natural gas and water vapor.

Principle of Flow Sensors

Flow sensors employ a variety of measurement formats depending on the nature of the fluid to be measured and the purpose of the measurement. This section describes the principle of differential pressure flow sensors, which are applicable to common fluids such as air and water.

The principle used in differential pressure flow meters is Bernoulli’s theorem. During the flow of a fluid of a certain size, if the flow path is intentionally narrowed, a pressure difference is created due to a pressure drop in the fluid. This pressure difference is applied to Bernoulli’s law to calculate the flow velocity.

There are various types of flow sensors, such as orifice-type and nozzle-type, depending on the mechanism used to narrow the flow path. However, they all share the same principle of measuring the pressure difference between the fluid before and after the narrowing mechanism.

How to Select a Flow Sensor

The appropriate flow sensor depends on the type of fluid to be measured. If you select the wrong flow sensor for a gas or a liquid, you will not only record the wrong flow rate, but also risk a serious accident, particularly if the chosen flow sensor is ill-suited for measuring the flow rate of a hazardous or flammable substance. Therefore, it is important to start by carefully examining the nature of the substance to be measured.

In addition, flow sensors generally cannot measure a wide range at once. If the expected flow rate is determined in advance, it is best to select a flow sensor with high accuracy for that range.

Other Information on Flow Sensors

1. About Clamp-on Type Flow Sensor

Clamp-on means that the instrument is mounted outside the piping through which the fluid to be measured flows. Clamp-on flow sensors include ultrasonic flow meters and ultrasonic flow sensors.

If the object to be measured is a fluid or other material that can be measured by ultrasonic waves, it can be used as a measurement device. Ultrasonic flowmeters include the propagation time difference method and the frequency measurement method using the Doppler method. The advantage of ultrasonic flowmeters is that they can be installed without removing or cutting piping, thus reducing the cost of installation.

Another advantage is that maintenance after installation is greatly improved and pressure loss in the piping is eliminated. Conversely, demerits include the need for a long straight pipe section since the meter is installed outside of the piping, the fact that the diameter of the piping is also a factor, and the fact that measurement cannot be performed if the fluid to be measured contains many solids or bubbles.

2. Air Flowmeter

Air flowmeters include clamp-on flowmeters and screw-connection flowmeters. The screw-connection type eliminates the need for an intuitive part, and the measurement device is compact and space-saving.

Conventional air flowmeters have used thermal mass flowmeters if the gas to be measured is a compressible fluid. There are several measurement methods for thermal mass flowmeters. In the capillary type, a flow element with ohmmeter is installed inside the tube and a heater is wound around the outside of the tube, and temperature sensors on both sides of the heater measure the flow balance.

However, thermal mass flowmeters are vulnerable to contamination and are not good in low-pressure environments, making them unsuitable for facilities with large amounts of oil mist. Currently, the flow sensor type is the most common type of thermal mass flowmeter.

This type is composed of a semiconductor flow sensor and can be used in low-pressure environments with a wide measurement range and without concern for contamination.

What Is a Linear Motor?

A linear motor is an electric motor that produces motion in a straight line, unlike conventional motors that generate rotational motion. It operates on the principle of magnetism, utilizing the attraction and repulsion of magnets or the Lorentz force to create propulsive force. This design allows for direct linear movement, eliminating the need for complex mechanisms required by traditional motors to convert rotational motion to linear motion.

Uses of Linear Motors

Linear motors are widely used in various applications, from linear motor cars, such as the linear bullet train which achieves high speeds with minimal frictional loss thanks to magnetic repulsion, to industrial equipment requiring precision, such as machine tools and semiconductor manufacturing equipment. They are also found in consumer products like electric curtains, shaving machines, camera autofocus systems, and even in the food industry, exemplified by revolving sushi restaurants.

Principle of Linear Motors

The operation of linear motors relies on magnetic attraction, repulsion, or the Lorentz force, akin to conventional motors but designed to produce linear instead of rotational motion. There are several types of linear motors, including linear induction motors, linear synchronous motors, linear DC motors, and linear stepping motors, each based on different principles of operation.

1. Linear Induction Motor

Utilizes electromagnetic induction for propulsion, driving an electromagnet across a magnet-aligned NS-SN using electric current. This type is preferred for industrial applications requiring high precision.

2. Linear Synchronous Motor

Operates on magnetic attraction and repulsion, with motion generated by altering the magnetic poles of fixed magnets in sync with movable electromagnets. This method is highly efficient, making it suitable for linear motor cars to reduce power consumption, with magnetic levitation trains using superconducting magnets to further minimize energy loss.

3. Other Methods

Linear DC motors and linear stepping motors are employed in actuators and precision control of optical equipment, respectively. Linear piezoelectric motors, though less efficient, offer high precision control and are used in precision machinery.

Other Information on Linear Motors

1. Speed and Precision of Linear Motors

Linear motors offer significant benefits in speed and precision, eliminating the need for reduction mechanisms and allowing for accurate positioning. They can operate over long distances and can be configured with multiple units working in unison. Despite challenges in control, thrust, and maintenance, advancements are continually made, increasing their application in precision tools like grinders and lathes, and contributing to environmental preservation efforts.

2. Cooling of Superconductive Linear Motors

Superconductive linear motors, essential for magnetic levitation trains, utilize superconducting magnets that operate at low temperatures with zero electrical resistance, thereby creating a powerful magnetic field without energy loss. Advances in cooling technologies, moving away from liquid helium to materials like bismuth-based copper oxide, allow for higher operational temperatures and more efficient, compact cooling systems, paving the way for the development of high-temperature superconducting magnets.

What Is a Power Inverter?

A power inverter is a device that transforms input current into alternating current (AC). It can convert both direct current (DC) and AC; in the case of AC, it first converts the input to DC, then back to AC with adjusted voltage and frequency. To distinguish it from power inverter circuits, which are part of its structure, it’s sometimes referred to as a power inverter device.

Uses of Power Inverters

Power inverters are commonly used in electrical products featuring motors, as they control motor rotation. Air conditioners, for example, utilize power inverters in their compressors to regulate motor speed, enabling precise temperature control beyond the simple on/off method. This not only improves functionality but also significantly enhances energy efficiency, which is why modern air conditioners are typically equipped with power inverters.

Principle of Power Inverters

The core components of a power inverter include a converter circuit, a capacitor, and an inverter circuit. The process involves converting AC to DC through a converter circuit, using diodes for rectification. The rectified current is stored in a capacitor and then shaped through charging and discharging to create a pseudo-DC current. This current is fed into an inverter circuit, where pulse width modulation (PWM) generates pulse waves of varying widths, combining to produce a pseudo-sine wave. This allows for the free manipulation of output voltage and frequency, characterizing voltage-type and current-type power inverters.

Other Information on Power Inverters

1. Merits and Demerits of Power Inverter Control

Advantages
Power inverters are primarily adopted for their energy-saving benefits, allowing for precise motor speed adjustments and enhancing the accuracy of temperature control in devices like air conditioners and oil consoles, compared to traditional on/off temperature regulation methods.

Disadvantages
However, power inverters can be costly, and their capacitors, being consumable components, require periodic replacement. The decision to use power inverters should be made after weighing these factors carefully.

2. Causes of Power Inverter Breakdown

Long-term use of power inverters may lead to overcurrent and overvoltage issues, often due to the lifespan of their electrolytic capacitors. These capacitors are sensitive to temperature; a 10°C increase can halve their lifespan. Particularly in devices like air conditioners used extensively in summer, capacitors can wear out quickly, leading to failure. Signs such as motor vibration or noise may indicate the need for early replacement, as capacitor deterioration can also result in swelling or leakage.

What Is an Aluminum Electrolytic Capacitor?

Aluminum electrolytic capacitors are small capacitors with high capacitance that use aluminum oxide as the dielectric.

Wet type capacitors use an electrolyte as the cathode, but dry type capacitors using solids such as conductive polymers with improved performance are also available. Because of their low price and high versatility, they are used in many products with electronic circuit boards, such as home appliances and personal computers.

Uses of Aluminum Electrolytic Capacitors

Aluminum electrolytic capacitors are used in a wide variety of products with electronic substrates in a wide range of fields, such as automobiles, home appliances, and industrial equipment, because they are smaller, have a larger capacity, and are less expensive than other capacitors.

Specific applications are as follows:

• Automotive Field
  Engine control units, advanced driver assistance systems, air bag controls, car stereos, car navigation systems
• Home Appliances
  Televisions, recorders, digital cameras, audio equipment, refrigerators, washing machines, air conditioners, microwave ovens, lighting fixtures, personal computers, TV game consoles
• Industrial Equipment Field
  Various manufacturing equipment, power conditioners for renewable energy

When used as power conditioners for renewable energy, many of them use 10 to 100 aluminum electrolytic capacitors. Due to their high versatility, the performance requirements for aluminum electrolytic capacitors are increasing year by year.

Principle of Aluminum Electrolytic Capacitors

Aluminum electrolytic capacitors use thin aluminum foil for the anode and cathode and aluminum oxide for the dielectric. Aluminum oxide is formed on the surface of the aluminum foil by an electrochemical oxidation process (chemical conversion).

The surface of the aluminum foil is made uneven by an etching process to increase the surface area. The capacitance of a capacitor is expressed by the following equation, which is proportional to the surface area of the dielectric and inversely proportional to its thickness.

Capacitance C = ε × S/d　
ε: Dielectric permittivity of dielectric S: Surface area of dielectric d: Thickness of dielectric

A disadvantage of aluminum oxide coatings is that they generate more leakage current than other capacitors because of the minute current flow when voltage is applied. The internal cathode of a wet aluminum electrolytic capacitor uses an electrolytic solution, which can leak in the event of a failure.

Another drawback is that the electrolyte may decrease due to electrolyte leakage or evaporation, resulting in low durability. Dry aluminum electrolytic capacitors, on the other hand, do not evaporate because conductive polymers are used for the internal cathode, and are more durable than wet capacitors.

Other Information on Aluminum Electrolytic Capacitors

1. Life Span of Aluminum Electrolytic Capacitors

Among electronic components, wet aluminum electrolytic capacitors are known to have a particularly short life span: while LSIs are required to operate for tens of thousands of hours, a typical aluminum electrolytic capacitor has a life span of 2,000 hours at 85°C and a highly reliable one of 5,000 hours at 105°C.

One of the reasons for the short life expectancy is the structure of aluminum electrolytic capacitors, in which the electrolyte impregnated in the insulating paper gradually leaks out from the rubber sealing section over time. When the electrolyte leaks out, the capacitance decreases and ESR (equivalent series resistance) will increase.

The life of an aluminum electrolytic capacitor is said to follow Arrhenius’ law (chemical reaction formula based on thermal energy) when the temperature is below the maximum operating temperature, and the life is approximately doubled when the temperature is 10°C lower. Therefore, an aluminum electrolytic capacitor with a life of 2,000 hours at 85°C will last 4,000 hours if used at 75°C, and 8,000 hours at 65°C.

Compared to other capacitors, aluminum electrolytic capacitors have a large ESR, and when a large current flows during operation, the inside of the capacitor generates heat. This heat generation causes the temperature of the capacitor to rise, which further promotes electrolyte leakage and shortens the life of the capacitor.

2. Polarity Indication on Aluminum Electrolytic Capacitors

Polarized capacitors are always marked with some kind of indication so that the polarity can be easily checked.

• Vertical Electrolytic Capacitor
  Generally, there is a line on the negative pole side below the body. Also, the lead wire of the negative electrode is shortened.
• Surface Mount Type Electrolytic Capacitor
  Capacitance and withstand voltage are indicated on the top surface of the electrolytic capacitor, and there is a colored mark in one corner. The electrode below this mark is the negative electrode.
• Axial Lead Type Capacitor
  The line with an arrow indicates the lead of the negative electrode. The electrolytic capacitor body has a recess; the side with this recess is the positive electrode.

It is extremely important to check the polarity indication because if the polarity is incorrectly marked, the capacitor may not only malfunction but may also catch fire.

What Is a Strain Gauges?

A Strain gauge is a device that measures the strain of an object. They have also been used in pressure gauges and force gauges because they can measure strain and calculate pressure, load, etc.

Uses of Strain Gauges

Strain Gauges are used to measure the strain of products whose strength is directly affected by strain, to measure loads in production plants, and to measure the degree of deformation of molds and other components. However, care must be taken to ensure that the strain cages are installed in the correct orientation, otherwise, measurement errors will occur.

Specific examples of use include the following.

• Measurement of strength and strain of printed circuit boards
• Monitoring and measuring the load on press equipment

Principles and Types of Strain Gauges

1. Principle of Strain Gauges

Strain cages are used by attaching them to the object to be measured, which is then strained along with the object to be measured, resulting in a change in the internal electrical resistance. The strain is calculated by measuring the amount of change in the electrical current.

2. Types of Strain Gauges

There is a great variety of strain gauge types. The most widely used are foil strain gauges, wire strain gauges, and semiconductor strain gauges.

Other features of strain gauges include those suitable for low and high-temperature environments, those capable of measuring finer strains, and those made of materials suitable for various materials to be measured.

Structure of Strain Gauges

The structure of  “foil strain gauges” and “semiconductor strain gauges” are described below.

1. Foil Strain Gauges

The structure of foil strain gauges, the most popular type of strain gauges, consists of a metal foil attached in a zigzag pattern on an insulator base, with two wires coming out of the metal foil. These two wires are connected to a circuit called a Hoinston bridge circuit.

The Hoinston bridge circuit is a circuit in which three resistors of known resistance and four strain gauges are arranged in a bridge configuration, and the resistance of the strain gauges can be measured by measuring the potential difference between the center of the resistors and the strain gauges.

When the object to be measured to which the strain gauges are attached is distorted, the foil of the strain gauges attached expands or contracts, resulting in a change in the value of electrical resistance, and the amount of change in resistance is obtained from the potential difference in the Hoisington bridge circuit. Since strain gauges have a gauge factor, which is an intrinsic value of the amount of change in resistance to strain, it is possible to calculate the strain of the object to be measured from the gauge factor and the amount of change in resistance.

2. Semiconductor Strain Gauges

Semiconductor strain gauges are strain gauges that utilize a semiconductor in the foil portion of a foil strain gauge. They utilize the property that the electrical resistivity of a semiconductor changes when stress acts on the semiconductor.

Other Information on Strain Gauges

1. How to apply Strain Gauges

The accuracy of strain measurement using strain gauges strongly depends on the method of gauge installation (adhesion in most cases). Therefore, it must be very careful when attaching strain gauges to a measurement object. The first step is to clean the surface of the measurement target to which the gauge is to be attached.

It is best to use an oil-based detergent to remove oil thoroughly. Failure to do so will allow oil to penetrate deeper into the material when the surface is ground or polished during application. After cleaning, lift the gauge with tweezers and carefully adhere it to the surface to be measured.

At this time, it is important to ensure that all empty bubbles between the surface and the gauge are pushed out so that they can be affixed. In this state, wait a few minutes for the adhesive to harden. After a few minutes have elapsed, finally wrap the entire surface with insulation tape to protect it from damage, and the pasting is complete.

2. Drawbacks of Strain Gauges and how to solve them

The advantage of strain gauges is that they can easily measure strain simply by bonding them to the object to be measured. In reality, however, there are many complex factors involved that make measurement more difficult. For example, the problem of stress is one of them.

Strain changes due to the material’s interaction between externally applied forces and internal stresses. Therefore, analysis of strain in two or three directions requires using “rosette strain gauges,” which are a combination of multiple gauges.

In addition, depending on the coefficient of thermal expansion of the material constituting the measurement object, the strain may be determined to have occurred even if there is no actual strain. To prevent this, it is necessary to match the material of the gauge with the material to be measured.

In strain measurement with strain gauges, the best one must be selected from among many types of gauges based on a good understanding of their physical or mechanical characteristics. 

3. Strain Gauges and Temperature Compensation

The major factors affecting strain gauges bonded to the measurement object are strain caused by external forces and temperature change. When temperature changes occur, the strain gauges are affected by the difference in the coefficient of linear expansion between the measurement object and the strain gauges, and by the change in resistance of the strain gauges due to temperature.

The measurement of strain as if it is caused by temperature change is called apparent strain. The use of self-temperature compensating strain gauges is the most effective countermeasure against apparent strain. Self-temperature compensating strain gauges are strain gauges in which the temperature coefficient of resistance of the strain gauges is adjusted to suit the measurement object to minimize the amount of apparent strain due to temperature.

Selecting the appropriate strain gauges for the measurement object is the best choice, but it may leave some errors. In some cases, they have nonlinear characteristics. In most cases, this error is noted on the data sheet of the strain gauges, and if more precise measurement is required, a compensation calculation can be made to account for the error calculated from the datasheet.

4. Strain Gauges and Creep Compensation

Creep is a phenomenon in which strain increases with time when a constant load is applied under certain temperature conditions. The creep phenomenon is the natural enemy of strain gauges, and if it occurs, it may directly lead to measurement errors.

In most cases, the creep phenomenon of strain gauges is caused by the base material, grid shape, and adhesive. Therefore, a common method is to cancel the effects of creep phenomena on each other by using a strain generator in the opposite phase of the creep caused by these factors as the material creep and attaching strain gauges to it.

The important point is the combination of materials. If the creep phenomena are in opposite phases, but their absolute values are very different, they cannot be canceled, and the effect will be in one direction. Note that, depending on the material, creep phenomena are more pronounced at higher temperatures in most cases. Please remember that the higher the stress applied to the strain gauges, the shorter the time to rupture (life), considering the increase in strain due to the creep phenomenon.

What Is a Positive Temperature Coefficient (PTC) Thermistor?

A PTC thermistor is an electronic component whose resistance value increases sharply at a certain temperature.

PTC stands for positive temperature coefficient, meaning that there is a positive correlation between temperature and resistance. Thermistor is derived from the term “Thermal Sensitive Resistor”. A thermistor is a component that can measure temperature from the difference in electrical resistance when a resistive element is brought into contact with the object to be measured. It is characterized by the use of a metal oxide semiconductor as the resistive element.

An overcurrent protection device using a positive temperature coefficient (PTC) thermistor is also called a resettable fuse. Tube and blade fuses use alloy elements that need to be replaced once they blow, so the principle is different from that of common fuses.

When an excessive current flows in a circuit, a resettable fuse limits the current value by causing the positive temperature coefficient (PTC) thermistor to become hotter and its resistance to increase. When the cause of the excessive current is removed, the positive temperature coefficient (PTC) thermistor decreases and its resistance becomes lower. Therefore, it is used as a resettable fuse.

Uses of Positive Temperature Coefficient (PTC) Thermistors

PTC positive temperature coefficients (PTC) thermistors are used in electronic circuit boards and a wide range of other applications, from home appliances to industrial applications. The following are examples of positive temperature coefficient (PTC) thermistor applications:

• Overcurrent and overload protection for smartphones, etc.
• Overload protection for small motors
• Electric carpets and heaters
• Overload protection for motors and power semiconductors

PTC positive temperature coefficient (PTC) thermistors have a low resistance value when the temperature is low, but when overheated due to excessive current, the resistance value increases rapidly. This mechanism allows them to be used for overcurrent protection in electrical circuits. Circuits in which PTC thermistors are used include heater circuits and electronic communication devices.

Protection against overheating must also be considered when using power semiconductors and motors. This is where positive temperature coefficients (PTC) thermistors are used. To protect against overheating, a positive temperature coefficient (PTC) thermistor is used by physically thermally coupling the PTC thermistor to a heat sink or motor winding for heat removal.

The positive temperature coefficient (PTC) thermistor is used to detect overheating by increasing its resistance, and the circuit is configured to stop operation or shut off the power supply.

Principle of Positive Temperature Coefficient (PTC) Thermistors

PTC thermistors have three major characteristics:

1. Resistance Temperature Characteristics

The resistance value is almost constant from room temperature to the Curie point (temperature at which the resistance value is about twice that of room temperature), and increases rapidly after the Curie point. This property allows the device to detect overheating of an electronic circuit quickly and limits the circuit current, thereby preventing failure of electronic components.

2. Static Characteristics (Voltage-Current Characteristics)

Until the Curie point is exceeded, the current rises in proportion to the rise in voltage. Once the Curie point is exceeded, the resistance of the thermistor itself increases, and the current value decreases. In other words, a constant power is maintained. The voltage-current characteristic is characterized by a mountain-like graph.

3. Dynamic Characteristics (Current-Time Characteristics)

The current-time characteristic of a PTC thermistor is characterized by the fact that the current value decreases over time. This characteristic allows a large current to flow immediately after the power is turned on, and is used for motor startup and other applications.

Types of Positive Temperature Coefficient (PTC) Thermistors

PTC thermistors can be classified into two types: polymer-based and ceramic-based.

1. Polymer Type

Polymer-based PTC thermistors are manufactured by mixing conductive particles with polymer materials, such as polyethylene. Carbon black and nickel are used as conductive particles.

They are also known by the acronym PPTC. Resettable fuses are also called poly switches, but the name is derived from the polymer. The positive temperature coefficient (PTC) thermistor is used only for overcurrent protection.

2. Ceramic-Based

PTC thermistors are positive temperature coefficient (PTC) thermistors made of ceramic with a small amount of rare earth elements added to barium titanate. Curie temperature can be adjusted by adjusting the amount and type of additives. They are used not only for overcurrent protection but also for demagnetization circuits and self-regulating heating elements.