From winding compensation to gain stabilization, there is almost nothing these devices cannot accomplish. To find out more information about designing and using thermistors, you should give us a call today! Thermistors offer many benefits, which is why they are widely used in many applications and industries. Thermistors are all around us, from life-saving medical equipment to HVAC systems that keep us comfortable.
Although these devices are affordable, powerful, and reliable, they suffer from certain limitations, which means they are not ideal for all applications. To calculate thermistor-resistance measurements, an individual needs a voltage measurement. The resolution of a voltmeter limits the accuracy of readings.
It is also important to keep in mind that input bias currents and input-offset voltage of operation amplifiers also directly affect accuracy. To properly measure resistance, all currents need to pass through a thermistor that dissipates heat. This results in a small temperature increase, which is labels as self-heating errors. This type of error functions in proportion to the dissipated power plus the thermal resistance of thermistors and the environment they function within.
Internal thermal resistance changes depending upon the material and dimensions of the thermistor, whereas external thermal resistance depends on the thermal conductivity level of the medium that surrounds the thermistor.
In many applications, self-heating is considered a serious problem for measurements that are made over an extensive temperature range. Stray thermal influences affect the performance of thermistors. Because of the high thermal resistance that is found between the environment and thermistor, the devices are prone to stray thermal influences.
The two main culprits are the heat that is conducted along lead wires and infrared radiation. The problem is often made worse when there is a poor thermal design. The problem is most often experienced when measuring surface temperature or air. Using Thermistors in Controlled Systems. Within a controlled system, thermistors have a specific function. A temperature controller is used to monitor the temperature of thermistors that then instruct a heater or cooler to turn on and off.
The goal is to maintain a consistent temperature within the thermistor and the target device. Some of the most commonly controlled systems that use thermistors include air conditioning units and refrigerators to name a few. Sensors have small amounts of currents, called bias currents, running through them.
The current is supplied from the temperature controller. Controllers do not read resistance, which means that it must be converted into voltage changes. This is done with the help of a current source that applies a bias current across the entire thermistor, hence producing controlled voltage.
A thermistor needs to be placed close to the device, requiring control to guarantee the highest levels of accuracy.
This can be done by attaching or embedding the thermistor. As the thermistor moves further away from the device, users experience greater thermal lag time that negatively affects the accuracy of temperature measurements.
Avoid placing thermistors away from thermoelectric coolers because that also reduces stability. Keeping thermistors close to devices ensures a quick reaction time to temperature changes. This is a key aspect of maintaining consistent temperatures within controlled systems.
Placement of a thermistor within a controlled system is the first consideration to make, and once that is finished, individuals can begin to determine base thermistor resistance, setpoint, and bias current. NTC Thermistors and Epoxy. Epoxy is often used to create a protective barrier for NTC thermistors , howver epoxy is not a waterproof seal. Engineers may use epoxy-protected thermistors to protect thermal conductivity and high dielectric strength.
These thermistors are tear-drop-shaped bead that has two radial wire leads. These thermistors are used in medical devices that measure air temperature and airflow. You may also find epoxy bead thermistors in automotive applications.
Protecting NTC thermistors from direct exposure to fluids is critical for the function of different devices. Thermally conductive epoxy can be used within a stainless-steel housing, but is not fully waterproof. Glass parts or laser welded parts that are hermetically sealed would be more ideal for moisture environments.
What is a Thermistor? A thermistor is a common type of semiconductor that is found in a wide range of applications and industries. Engineers turn to thermistors because they are highly accurate while also being cost-effective. NTC thermistors are constructed from various materials that all have known resistance. Materials are the largest factor in determining the shape of resistance and temperature curves. Most thermistors are subdivided into two categories: Low-Temperature Applications The temperature range for these applications is often considered below 0C.
High-Temperature Applications These applications often work in larger devices or systems such as automotive and industrial applications etc. Engineers and designers choose thermistors when their applications demand ruggedness, stability, and reliability. These sensors are ideal for environments that have extreme conditions and the presence of electronic noise.
To meet the demand of engineers, thermistors are available in different shapes, materials, and sizes. The idea shape for an application largely depends on the type of material being measured. NTC thermistor probes are used for measuring temperature and liquid levels for industrial, commercial, and residential purposes.
These sensors are integral tools for many industries, so they are often included in medical technologies, green energy, and automotive electronics. These probes range in size, shape, and application, so it is essential to utilize sensors that fit exact needs.
NTC thermistors are necessary when you are constructing devices and technology that are used to preserve life, for example, ventilators. Temperature sensors must be extremely sensitive and responsive.
NTC thermistors are necessary for the development and proliferation of renewable energy sources. For example, an NTC thermistor can be used to offer better braking systems within small wind turbines.
In wind turbines, traditional breaking circuits are known to damage the rotors of turbines. Thermistors also play an important role in monitoring the temperature of blades operating in cold environments. NTC thermistors are necessary for the continued innovations within the automotive industry. Many of the standard applications we have expected in new cars would not function without the thermistor's feedback and control.
For reference, in the s, a car on average would have two to five thermistors, whereas today, you are likely to find upwards of NTC Thermistors. Thermistors have a place in everyday applications, such as portable heaters and freezers. They are ideal in a preventative capacity. Common Thermistor Configurations.
Thermistors are semiconductors that offer greater resistance than a conducting material while also maintaining lower resistance than an insulating material. The materials used to construct a thermistor are among the main factors in determining the relation between temperature and resistance.
When searching for thermistors, you need manufacturers that determine resistance properties to a high degree of accuracy because this is the main characteristic of interest for purchasing thermistors. After working on resistance, you need to turn attention to thermistor configurations.
These devices are sold in various configurations, but some common are: Hermetically Sealed Thermistors This configuration type is sealed usually in glass that protects the sensing element from moisture etc. This configuration is more ideal for measuring temperature in a wide array of liquids. Surface-Mounted Thermistor The main benefit of these thermistors is that they can be used on circuit boards and lay flat, with a small overall footprint.
They beneficial in many industrial and commercial applications. They have a small thermal mass that allows them to respond to temperature changes quickly. These thermistors are found in many applications, including household appliances, equipment, and pipe casings. An NTC thermistor is a thermally sensitive resistor.
Use an NTC thermistor when you need resistance to decrease when temperature increases. Precise monitoring and responses to temperature change are the jobs of a thermistor.
In some cases the Pt will work better and be more accurate. The Pt is widely used in many industrial and commercial applications. The Pt is better suited to 3 and 4 wire circuit configurations than the 2 wire configuration. This is due to an important Pt sensor working principle: because resistance across the sensing element is considerably lower than in the Pt, unwanted resistance from lead wires and connectors will have a larger distorting effect on overall resistance measurements, since it will comprise a greater percentage of the total resistance measured in the circuit.
The lead wire resistance is measured and compensated for by an instrument that accepts the 3 or 4 wire configurations. Pts are available with both thin-film and wire-wound element constructions. Pts are compatible with a broader range of products and instrumentation because their use is so widespread. Pt sensors are suitable for use in applications with 2 wire circuit configurations. Since the Pt sensor has much greater resistance, the distorting effect of the resistance in the lead wires is less significant overall because it makes up a smaller percentage of the total resistance in the circuit.
Linearity of the characteristic curve, operating temperature range, and response time are the same for both. The temperature coefficient of resistance is also the same. However, due to the different nominal resistance, readings for Pt sensors are higher by a factor of 10 compared to Pt sensors. This difference becomes evident when comparing 2-wire configurations, where lead measurement error is applicable.
Both types of sensors work well in 3- and 4-wire configurations , where the additional wires and connectors compensate for the effects of the resistance of the lead wires on the temperature measurement.
The two types are also similarly priced. Pt sensors, however, are more popular than the Pt for a couple of reasons:. So, why would someone opt for the Pt sensor instead? Here are the situations where the greater nominal resistance has the clear advantage:. In general, Pt temperature sensors are more commonly found in process applications, while Pt sensors are used in refrigeration, heating, ventilation, automotive, and machine building applications. The issue that users must watch out for when replacing existing Pt and Pt sensors is the regional or international standard.
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