Temperature sensors are being used in diverse applications for example food processing, HVAC environmental control, medical devices, chemical handling and automotive underneath the hood monitoring (e.g., coolant, air intake, cylinder head temperatures, etc.). Temperature sensors often measure heat to make certain that an operation is either; staying within a certain range, providing safe consumption of that application, or meeting a mandatory condition when dealing with extreme heat, hazards, or inaccessible measuring points.
There are two main flavors: contact and noncontact temperature sensors. Contact sensors include thermocouples and thermistors that touch the object they can be to measure, and noncontact sensors study the thermal radiation a heat source releases to find out its temperature. The second group measures temperature from a distance and often are used in hazardous environments.
A temperature sensor thermocouple is a pair of junctions which can be formed from two different and dissimilar metals. One junction represents a reference temperature and also the other junction may be the temperature to become measured. They work each time a temperature difference creates a voltage (See beck effect) that may be temperature dependent, and that voltage is, consequently, converted into a temperature reading. TCs are employed because they are inexpensive, rugged, and reliable, do not demand a battery, and works extremely well more than a wide temperature range. Thermocouples can achieve good performance approximately 2,750°C and can also be employed for short periods at temperatures approximately 3,000°C and only -250°C.
Thermistors, like thermocouples, may also be inexpensive, easily available, user friendly, and adaptable temperature sensors. They are utilized, however, to adopt simple temperature measurements rather than for high temperature applications. They are constructed with semiconductor material with a resistivity that is certainly especially sensitive to temperature. The resistance of your thermistor decreases with increasing temperature to ensure that when temperature changes, the resistance change is predictable. These are popular as inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements.
Thermistors change from resistance temperature detectors (RTD) because (1) the content utilized for RTDs is pure metal and (2) the temperature response of these two is different. Thermistors may be classified into two types; according to the indication of k (this function refers back to the Steinhart-Hart Thermistor Equation to convert thermistor resistance to temperature in degrees Kelvin). If k is positive, the resistance increases with increasing temperature, as well as the device is called a positive temperature coefficient (PTC) thermistor. If k is negative, the resistance decreases with increasing temperature, along with the device is called a negative temperature coefficient (NTC) thermistor.
For instance of NTC thermistors, we are going to examine the GE Type MA series thermistor assemblies intended for intermittent or continual patient temperature monitoring. This application demands repeatability and fast response, especially when combined with the care of infants and during general anesthesia.
The MA300 (Figure 1) makes routine continuous patient temperature monitoring feasible by utilizing the comfort of the patient’s skin site being an indicator of body temperature. The stainless-steel housing used is suitable for both reusable and disposable applications, while maintaining maximum patient comfort. Nominal resistance values of 2,252, 3,000, 5,000, and ten thousand O at 25°C are offered.
Resistance temperature detectors (RTDs) are temperature sensors using a resistor that changes resistive value simultaneously with temperature changes. Accurate and recognized for repeatability and stability, RTDs works extremely well by using a wide temperature range from -50°C to 500°C for thin film and -200°C to 850°C to the wire-wound variety.
Thin-film RTD elements use a thin layer of platinum over a substrate. A pattern is produced that provides a power circuit that may be trimmed to give a certain resistance. Lead wires are attached, and the assembly is coated to guard the two film and connections. Compared, wire-wound elements can be coils of wire packaged within a ceramic or glass tube, or they could be wound around glass or ceramic material.
An RTD example is Honewell’s TD Series used for such applications as HVAC – room, duct and refrigerant temperature, motors for overload protection, and automotive – air or oil temperature. Within the TD Series, the TD4A liquid temperature sensor is really a two- terminal threaded anodized aluminum housing. The environmentally sealed liquid temperature sensors are designed for simplicity of installation, including within the side of the truck, however are not created for total immersion. Typical response time (for just one time constant) is four minutes in still air and 15 seconds in still water.
TD Series temperature sensors respond rapidly to temperature changes (Figure 2) and they are accurate to ±0.7C° at 20C°-and are completely interchangeable without recalibration. They are RTD (resistance temperature detector) sensors, and offer 8 O/°C sensitivity with inherently near-linear outputs.
RTDs have got a better accuracy than thermocouples and also good interchangeability. They are also stable in the long run. With such high-temperature capabilities, one can use them often in industrial settings. Stability is improved when RTDs are made of platinum, that is not impacted by corrosion or oxidation.
Infrared sensors are utilized to measure surface temperatures ranging from -70 to 1,000°C. They convert thermal energy sent from an item in the wavelength range of .7 to 20 um into an electric signal that converts the signal for display in units of temperature after compensating for virtually any ambient temperature.
When selecting an infrared option, critical considerations include field of view (angle of vision), emissivity (ratio of energy radiated by an object to the energy emitted with a perfect radiator on the same temperature), spectral response, temperature range, and mounting.
A recently announced product, the Texas Instruments TMP006, (Figure 3) is definitely an infrared thermopile sensor in the chip-scale package. It really is contactless and works with a thermopile to absorb the infrared energy emitted through the object being measured and uses the corresponding alternation in thermopile voltage to determine the object temperature.
Infrared sensor voltage range is specified from -40° to 125°C make it possible for utilize in a wide range of applications. Low power consumption in addition to low operating voltage makes the dexopky90 ideal for battery-powered applications. The reduced package height of your chip-scale format enables standard high volume assembly methods, and will be useful where limited spacing towards the object being measured is offered.
The use of either contact or noncontact sensors requires basic assumptions and inferences when employed to measure temperature. So it is very important read the data sheets carefully and be sure you possess an understanding of influencing factors so you may be positive that the particular temperature is the same as the indicated temperature.