Frequently Asked Questions

Thermistors are thermally sensitive resistors, which show a precise and predictable resistance change in direct proportion to their change in temperature.

There are 2 main types of Thermistor:

NTC Thermistors (Negative Temperature Coefficient) whose resistance drops as the temperature increases.

PTC Thermistors (Positive Temperature Coefficient) whose resistance increases rapidly as the temperature increases.

The differences are readily explained in the below diagram;

ATC Semitec stocks a wide range of both NTC thermistors and PTC thermistors which can be readily viewed via this page website

However if you have more detailed questions or need samples for your new application, then please call one of our engineers today on 01606 871680, or complete our contact form

Thermistors are very simple to incorporate electronically (and physically) as they exhibit a large change in resistance/°C when compared with other sensor types.

So they are very robust, available in numerous form factors and can be readily used from -60°C to +300°C.

Typical applications for thermistors include: 

Temperature Measurement

Temperature Control

Temperature Compensation

Inrush Current Limiting

Over-Temperature Solid-State Switches

ATC Semitec stock a wide range of both NTC and PTC thermistors which can be viewed here website

If you have a question or need a sample, then call one of our engineers today on 01606 871680 or complete the contact form

NTC Thermistors (Negative Temperature Coefficient) are basically thermal resistors whose resistance drops when the temperature increases.  When the term thermistor is used, engineers often mean NTC thermistors.

An NTC thermistor has a high resistance at low temperature, and as the temperature increases the resistance decreases rapidly. Therefore NTCs offer the benefit of highly accurate and quick response times to very small changes in temperature.

These are generally used for temperature measurement as their RT (Resistance – Temperature) characteristic is very well defined and can be readily programmed.

Thermistors are manufactured from metal oxide semiconductor materials encapsulated in impermeable materials such as epoxy or glass. These coatings protect the thermistor bead and lead-wire connections mechanically whilst also providing protection against humidity.

To see our full range of NTC Thermistors on our website click here

Have a question or need a sample ? Call one of our engineers on 01606 871680

NTC thermistors have a high temperature coefficient of resistance (TCR), are very stable and have excellent repeatability.  Readily available in numerous form factors, they are also;

Highly accurate (± 1% tolerance or better)

Thermally very fast (Tc ~1s)

Very compact (SMD, thin-film and tiny beads)

Low-cost (highly competitive)

Interchangeable – No re-calibration required

Point matching – Can be calibrated at a specific working temperature

Wide temperature operating range (-60°C/+300°C).

They are also highly customisable to suit your application.

Have a question or need a sample? Call one of our engineers today on 01606 871680

NTC thermistors are used in a large number of temperature sensors in everyday life and include :-

• Home appliances (Temperature control of ovens and fridges)
• Personal care (Hair-dryers, stylers)
• Medical devices (Catheters, thermometers, glucose monitors)
• Smart devices/IOT products (Home automation, domotics)
• Battery monitoring (Overcharge, over-discharge)
• Automotive/E-Vehicles (Cabin temp, battery monitoring, EGR)
• HVAC appliances (Air temperature, condenser temps)
• Fire & security (Heat detectors, smoke detectors)
• Office automation (Copier & laser printer fuser rollers)

Some larger disc NTC thermistors (or power thermistors) are used for current inrush limiting.  They offer a neat, cost-effective solution to surge currents arising from switching on some electronic or electrical products, e.g. Switch Mode Power Supplies, LED drivers and halogen lamps or heaters.

Have a question or need a sample?  Call one of our engineers today on 01606 871680

NTC thermistors can be supplied in different configurations/housings depending on your applications:                     

Epoxy coated generally for lower temperature use (-60°C to +150°C)

Glass encapsulated ideal for use in high temperature applications ( -50°C to +300°C)

In temperature probe assemblies – with IP67 or IP68 ratings if required.

SMD (surface mount) packages down to 0201 size

Threaded or boss mounted, metal encapsulated temperature sensors.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

PTC stands for “Positive Temperature Coefficient“. PTC thermistors are thermally sensitive resistors with a positive temperature coefficient, which means that the resistance increases with increasing temperature.

This is in contrast to an NTC thermistor whose resistance decreases with the increase in temperature.

To view our range of PTC Thermistors on our website click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680

There is no easy formula in deciding which is the best NTC thermistor for your application as there are many different factors to take into consideration.

Factors to take into consideration include levels of accuracy, resistance values, shapes and size.

At ATC Semitec we have more than 25 years of experience in providing thermal solutions for industry. Give us a call today for expert technical advice, and to request samples.

Call 01606 871680

A thermal fuse (or thermal cut-off or “tco”) is a one-shot/one-time, non- re settable, temperature-sensitive device that provides ultimate overheat temperature protection in small appliances, electric heaters and electronic circuits.

Thermal fuses are fail-safe devices which activate when other safety measures fail to operate. They help  prevent temperatures rising to dangerous levels, and  thus stop product fires from occurring. The original fault in the appliance could have been caused by either control malfunction or customer misuse.      

Thermal fuses therefore offer the ultimate thermal protection.

They are single use protection devices that cannot be reset or repaired. They have to be replaced once the original fault which caused the product failure has been identified and rectified. In the case of many consumer products, this would mean replacing the complete appliance.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Thermal fuses are generally used to protect electric heaters, household electrical appliances and electrical products used in hazardous areas.                 

Specific examples include

• washing machines
• tumble dryers
• convector heaters
• coffee makers
• hair dryers
• laser printers
• rechargeable battery packs..

When designing with a thermal fuse, you need to consider the operating current, applied voltage and the duty hours of the appliance that it will protect.  The normal running temperature needs to be a minimum of 25°C below the fuse opening temperature not including any self-heating due to I²R/ current self-heating. The Th (holding temperature) and Tm (maximum temperature) values stated for the fuse should also be taken into account. This is to ensure reliable operation over the required product life, and that any IEC/EN standards they are approved to, are complied with.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

We have an array of thermistors suitable for medical temperature sensing, with our F-Micro Miniature Thermistor having a multitude of applications due to its small size and precise design. These allow it to be easily supplied in tubes as small as 0.28mm, and combined with a high thermal accuracy of 0.14K at 37°C make it our most advanced thermistor available.                                                                                                           

For non-contact applications, the NC temperature sensor utilises the latest FT thermistor technology to sense infrared energy with a high signal strength.

For a full range of our products suitable for medical applications, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

ATC Semitec stock a number of different types of thermal fuse:

Organic pellet – see SEFUSE SF/R types for details

Eutectic solder alloy –  see SEFUSE SM/A types for details

Bimetal element –  see PEPI H types for details

Have a question or need a sample ? Call one of our engineers today on 01606 871680

SEFUSE SF  series pellet thermal fuses are housed in a metal casing.  The organic thermal pellet inside responds to external high temperatures and close to its set-point, will start to melt.  As the pellet melts, it triggers a spring-loaded contact mechanism which breaks the electrical circuit as shown in the diagram below;

The SF-R thermal fuse contains a sliding contact, springs, and a thermal pellet inside a metal case. When spring B is compressed, contact between lead A and the sliding contact is maintained. At normal temperatures, current flows from lead A to the sliding contact and then through the metal case to lead B.

When the ambient temperature rises to the SEFUSE operating temperature, the heat transferred through the metal case melts the thermal pellet. When the thermal pellet melts, spring A and B expand, moving the sliding contact away from lead A. The electrical circuit is opened by breaking contact between the sliding contact and lead A.

To view our full range of Organic Pellet Thermal Fuses click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680

SEFUSE SM series solder-based thermal fuses are housed in a ceramic case.  The solder alloy inside responds to external high temperatures and at its set-point, will start to melt.  As the solder melts, it separates to either end of the case (helped by the surrounding flux) and thus breaks the electrical circuit.  See diagram below;

In the SM type, leads are connected by a fusible alloy. The current flows directly from one lead to the other. The fusible alloy is coated with a special flux.

When ambient temperature rises to the SEFUSE operating temperature, the fusible allow melts and condenses into a drop around the end of each lead because of the surface tension and the coating of special flux. The electrical circuit then opens.

To view our full range of Eutectic Solder Alloy Thermal Fuses click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680

PEPI H series bi-metal fuses use a snap-action bi-metal temperature-sensing element instead of a melting solder or organic pellet.

At its set-point, the specially designed bi-metal element inverts (i.e. “snaps” from concave to convex) and opens a set of contacts, thus breaking the electric circuit.

Bi-metal fuses do not suffer from ageing (e.g. shrinking of pellet fuses or sagging in solder fuses) and so are more reliable, especially at temperature settings above 200°C.  These bi-metal fuses will not reset even at ambient temperatures as low as -35°C.

Also available in ½”disc (button) thermostat housings such as our Asahi US-622 series.

To view our full range of thermal fuses  click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Circuit protection devices protect the circuit from excessive temperatures, currents or short circuit in an electrical conductor. They are essentially ‘weak links’ within the circuit that are designed to fail when a fault in the system is encountered. By breaking at low currents, they limit the amount of energy that is released during electrical failure, leading to safer devices.

From PTC resettable fuses, to CRDs, to MOV’s, we have an array of different devices to that can be implemented.

To see our full range of Circuit Protection Devices, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

There are many different types of circuit protection devices due to the multiple different ways that current can be limited in a circuit. At ATC Semitec, we have a range of different circuit protects to suit your appliance.

From our repeat use Inrush Current Limiters from Thinking TKS, designed to protect front-end mains voltage supplies against current spikes at switch-on, to our SEFUSE Thermal Fuses from SCHOTT which offer one-shot ultimate thermal protection from 70°C to 240°C, our range can tailor to your requirements.

For more information, and to see our full range of devices, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Metal oxide varistors are used to control high transient voltage surges in electronics and electrical circuits to safe levels. When a voltage surge exceeds the specified voltage, the varistor supresses the voltage to protect the circuit.

In general, a varistor (variable resistor) is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor, it has a nonlinear, non-ohmic current–voltage characteristic that is similar to that of a diode. But, unlike a diode, it has the same characteristic for both directions of traversing current.

At low voltage it has a high electrical resistance which decreases as the voltage is raised.

The advantages if using a varistor over other transient suppressors include;

Improved peak handling capability

High speed of response

High level of reliability – operating even at high temperatures

Offers cost- effective and compact solution.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

PTC or Polymer PTC (PPTC) fuses carry current up to a threshold temperature. At this point, the crystalline polymer structure will change to an amorphous state, leading to a massive increase in resistance, preventing charge from being carried across the device.

The device will then remain in this high resistance state until the applied voltage is removed and they have cooled down, allowing the polymer structure inside to return to its original crystalline form. Hence, they are considered re-settable. 

At ATC Semitec, we have a range of different PTC resettable fuses for use over many currents and operating temperatures.

To have a look at our current range of devices, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Circuit protectors offer circuit protection in devices in a manner that is far superior to using fuses.

This makes them ideal for applications containing:

Relay circuits

Motors

Heaters

Transformers

Solenoids

Semiconductors

Our CRD‘s from Semitec have a wide range of operating voltages that they can steady current over, and their small size makes them a neat solution in tight spaces.

CRDs, current regulating diodes, are diodes that maintain a constant current flow despite fluctuations in the voltage, over a wide range of voltage, from less than 1V to 100V.                     

Creating a constant current circuit generally involves multiple components. At ATC Semitec, we supply CRDs by Semitec, which provide the same function but as a single component.

This provides a concise, cost effective solution where space is limited.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Thermostats are used to control temperature and are present in many household appliances.

They are thermally sensitive switches which sense the temperature of either a heat source or a cooling device. The thermostat then controls this heat/cool source at a pre-set temperature within a predetermined differential, i.e. the difference in temperature between the thermostat switching on and off, on and off, etc.

The primary function of a thermostat is to control temperature.  Thermostats can either be pre-set, adjustable and are either electro-mechanical or electronic in form.

To view our full range of thermostats click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Thermostats can be used anywhere that requires heating or cooling controlled to a set temperature.

This could include;

Kitchen appliances – e.g. refrigerators, ovens, kettles, etc.

Water heaters, electric showers

Air conditioning and heat pumps

Catering equipment

Home automation

To view our full range of thermostats click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680

The most common form of thermostat is the electro-mechanical thermostat, which is often made up of a bimetal sensing element and contact switch mechanism. The bimetal element expands differentially with the change of temperature. When the thermostat reaches its set-point, the bimetal element activates the contact mechanism to stop the heating process.

Mechanical thermostats are therefore unable to control to an exact temperature but only within a temperature range defined by the thermostat. They are often used as simple On/Off switches.

Electronic thermostats use electronic sensors such as thermistors, platinum sensors or thermocouples to sense the change in temperature.  Any temperature change is then transmitted back to the electronic control circuit, where a relay is activated to help control to the pre-set temperature.

Electronic thermostats are more complex and therefore more expensive but can often accurately control a set temperature to within 1°C or less.  Whilst this could readily translate into money saved through energy savings, their use is often limited to ‘premium’ products and critical applications.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Adjustable Thermostats work in a similar way to regular bimetal thermostats, but have an adjustable spindle, which can be used to accurately set the temperature that the thermostat will activate.

ATC Semitec sells an array of Adjustable Thermostats from Campini, that can be used for both air and surface sensing. With a variety of temperature ranges these thermostats can be adjusted to, they provide ideal solutions for whatever your application is.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

ATC Semitec offers various types of thermostat depending on your application, accuracy and expected life-time of your product (duty hours).

Precision Thermostats

High accuracy Matsuo MQT series precision thermostats offer unrivalled accuracy and switching differential compared to other electro-mechanical controls.  They use a unique twin bimetal system to maximise accuracy, contact life and performance

Disc-Type Thermostats

Button or disc type bimetal thermostats are ubiquitous and are more widely used than any other type of bimetal thermostat.  Capable of switching high loads (up to 16A/230VAC) for over 10,000 cycles and also control within a 10K temperature differential, they offer low-cost control solutions for millions of home appliances and automotive uses.

Low-Profile Thermostats

PEPI bimetal thermostats are some of the smallest available worldwide and can offer accurate control from 5°C to 200°C.  Both creep-action and snap-action contact options help to make these one of the widest thermostat ranges, with control options for both low voltage and mains voltage applications.

Adjustable Thermostats

These types of thermostat use a relatively large bimetal blade which is flexed by means of an adjusting spindle.  Turning the spindle moves the bimetal blade either closer to or further away from the switching mechanism, thus creating a temperature “range”.  By varying the bimetal materials and thermostat design, control from 5°C to 300°C can be readily achieved whilst switching loads of up to 16A/230VAC

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Thermal cut-outs (or thermal switches) are a re-settable, temperature-sensitive device, which open at high temperatures, stopping current flow, and the re-close as the temperature decreases.

The opening and closing of the device is due to a bi-metallic element, which changes shape instantaneously with a change in temperature. They can either reset automatically, or manual reset options are available when an automatic and unattended restart could create a hazardous condition.

Thermal cut-outs are therefore used as fail-safe devices, preventing temperature from rising to dangerous levels, whilst their ability to reset makes them ideal for applications where high temperatures are reached frequently, without the need to replace the appliance.

We offer a range of products from world leading manufacturers, PEPI and Asahi in either probe or disc formats

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Bimetallic elements (or Bimetals) are comprised of 2 metals with differing thermal expansion coefficients, that are fixed together. As the element is heated, one side will expand at a faster rate than the other, resulting in unidirectional bending.

By altering the shape of the element at ambient temperature, the shape change can be made instantaneous, hence bimetals are often found as either curved discs or strips, which will ‘snap’ into shape.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

There are 2 types of thermal cut-outs that we sell here at ATC Semitec:

Snap Action Disc Thermal Cut-Outs, supplied by either ASAHI or EAW, which use a bimetallic disc.

Probe Thermal Cut-Outs, supplied by PEPI, which contain a bimetallic strip element.

PEPI’s JS Self-Hold Thermal Cutout includes an integral “self-hold” thermal and current sensitive cut-out allowing the protector latches to open after tripping and then reset remotely. This offers the same benefit as fitting a manual-reset cut-out but without the disadvantage of having to access it.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Thermal cut-outs are generally used in appliances that expected to frequently reach high temperatures, where the temperature needs to be carefully controlled up to a specific limit. The re-settable nature of thermal cut-outs make them ideal for repeated use in devices with cyclic thermal loading.

A prime example of this is kettles, but they are also frequently used air conditioners, motors, and an array of other kitchen appliances.

As they rely on bimetal elements, their thermal cut out temperature can vary significantly depending on the metals used and shape of the element. This results in thermal protection of devices over significant temperature ranges. The ASAHI US-622, for example, has an impressive operational temperature range of 0°C to +185°C.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

A temperature sensor is a device that collects information about the temperature of the surrounding environment by relating the changes in temperature to the change of a physical characteristic. This information can then be used to interpret the temperature of the device in an understandable form that can be ‘read’ by the device or observer.

Different types of temperature sensors are as follows:                                         

Thermocouples

Resistor temperature detectors

Thermistors

Infrared sensors

Have a question or need a sample ? Call one of our engineers today on 01606 871680

With the continual growth of the electric automotive industry, at ATC we ensure that we stock a range of temperature sensors suitable for the market. E-vehicle battery sensors need to be small, accurate, robust and fast responding, and our surface temperature sensors cover all these key parameters and more.

Our range includes :                                                                                                         

Ring Terminal Sensors, such as our top seller the STS2 Series Ring Terminal.

Flexible Film Sensors, like Semitec’s ultra thin JT NTC Thermister.

SMD NTC’s, encompassed in our Miniature SMD NTC Thermister range.

To see our full range of products suitable for e-vehicles, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Temperature sensors can be split into either:

Contact Temperature Sensors – which are required to be in physical contact with the object being sensed, using conduction to monitor changes in temperature.

Non-Contact Temperature Sensors – which use convection and radiation to monitor changes in temperature of an object without the need to be in contact with it.

To view our full range of temperature sensors click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Temperature sensors are required in any application where temperatures need to be carefully monitored.

At ATC Semitec, we have a whole range of sensors suitable for an array of applications, such as:   

Boiler Temperature Sensors 

Miniature Medical Temperature Sensors

E-Vehicle Temperature Sensors

And many more. To see our full range of temperature sensors, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Some temperature control applications require a very fast thermal response of 1 second or less, such as domestic showers and instant water heaters. This can be done to maximise thermal efficiency or avoid potential scalding.

At ATC Semitec, we stock a number of Very Fast-Response Temperature Probes. The thermal path to the thermistor is reduced in these sensors by situating the NTC thermistor in the very tip, minimising the thermal response time. Response times can be further accelerated by using our Thin Wall Tip or Exposed NTC Sensor.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

For gas boiler temperature control, a very fast thermal response is usually required to ensure accurate temperature control of the hot water. This helps provide sufficient quantities, maximise boiler efficiency and also avoid the possibility of scalding.                                                                                                           

At ATC Semitec, we stock a number of immersion and clip-on temperature sensors, where the NTC thermistor is situated in the very tip of the sensor similar to our Very Fast-Response Temperature Probes.

To view our full range of temperature sensors for boilers, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

We have an array of thermistors suitable for medical temperature sensing, with our F-Micro Miniature Thermistor having a multitude of applications due to its small size and precise design. These allow it to be easily supplied in tubes as small as 0.28mm, and combined with a high thermal accuracy of 0.14K at 37°C make it our most advanced thermistor available.                                                                                                           

For non-contact applications, the NC temperature sensor utilises the latest FT thermistor technology to sense infrared energy with a high signal strength.

For a full range of our products suitable for medical applications, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

The type of element used, is usaully guided by the  requirement of the specific application  however typically, the default  is a Thin Film Element.

Intrinsically vibration-resistant and lower in cost
than a Wirewound Element, the Thin Film Element meets the needs of most temperature
sensing applications.

The following table summarises the advantages of each type:

Our Heraeus Thin Film Elements differ primarily by their operating temperature range.

The table below summarises the various types.  It is important that the min/max operating temperature of your application falls within the operating range specified. Using a part outside the rated operating range may produce unpredictable results.

For detailed information please see individual data sheets on our website or call us on 01606 871680.

For a new application, we typically recommend the M222 type (2.3mm L x 2.1mm W). The M222 has a relatively low unit price, and will fit in a variety of probe sizes. For existing applications, a larger size element, such as the M1020 (9.5mm L x 1.9mm W) may be required to match an existing size footprint.

The following table summarises some size dependent properties.

The temperature coefficient, also referred to as the “alpha value”, is the average change in resistance between 0 and 100 °C, and calculated using the formula.

Where R100 is the resistance at 100 °C and R0 is the resistance at 0 °C.

Heraeus supplies Thin Film Platinum RTD Elements with the following temperature coefficients:

3850ppm
3750ppm (Pt1000 only)
3770ppm (Pt200 for automotive application only)

The self-heating constant defines the temperature rise in degrees Kelvin per mW of applied power. The constant of each RTD Element is measured in a standard condition of ice water at 0 Deg C. Since the constant is measured under conditions that don’t necessarily reflect a typical application environment, the self-heating constant is primarily used to compare the self-heating properties of one element to another. In addition, the actual use conditions greatly influence the self-heating constant. For example, potting the element in a thermally conductive material increases the surface area and thermal mass, effectively lowering the self-heating constant. If an element is used in a full or partial vacuum, however, the opposite can occur—the self-heating constant can increase due to the reduced thermal conductivity of the surrounding medium. In temperature-sensing applications, self-heating, if excessive, can introduce significant measurement error. The dependency of self-heating on the thermal conductivity of the surrounding medium can also be exploited to measure fluid level, flow,
thermal conductivity, fluid density, etc.