Technical Notes

Temperature Monitoring in Concrete Maturity

Temperature Monitoring in Concrete Maturity

MEI 26/05/2018 0
Concrete maturity indicates how far curing has progressed. Maturity is the relationship between concrete temperature, time, and strength gain. It is represented by an index value that can be measured in real time in the field. The maturity method, often simply referred to as maturity, is a way of evaluating new concrete’s in-place strength by relating time and temperature measurements to actual strength values.To expedite schedules, increase safety, and improve construction methods, construction teams want to know the strength of their concrete at the job site in real time. Since maturity is related to concrete strength, the maturity method is a way to accomplish this without solely relying on standard test specimens and laboratory testing.Maturity is calculated by tracking changes in fresh concrete temperature over time. Since each concrete mix has its own strength-maturity relationship, we can use maturity to estimate the strength of that mix at any moment after placement. When we know the maturity of a certain concrete, we can use that concrete’s specific strength-maturity relationship.When using the maturity method, construction teams can estimate real-time strength gain of in-...
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Thermistor and Water

Thermistor and Water

MEI 20/05/2018 0
An NTC thermistor is designed to measure temperature changes in different applications, but it is truly ideal for working in liquids (such as water). This is a result of long-term reliability and stability. They are the most accurate temperature gauges (when compared to a thermocouple), which allows for extremely close readings.A thermistor placed in water will most likely stay in one place for extended periods of time. A thermistor offers long-term durability for thermistor in water-based applications. A thermocouple will begin to weaken, which degrades its ability to read temperature accurately. Having to consistently replace thermocouples will intermittently stop production.A study about water temperature changes in Lake Tahoe has just recently ended. It was a 40-year study that suggests global warming is responsible for an increase in temperature in the lake (there has been a consistent rise over the last four decades). This is a big problem for the current habitat of the lake, and the warmer water threatens to destroy the whole eco-system.NTC thermistors were extensively used for this study because of their high accuracy rates. The thermistors helped to prove that the temperat...
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Basic Knowledge of Thermistor

Basic Knowledge of Thermistor

MEI 07/02/2018 0
What is a Thermistor?Thermistors (thermal resistors) are temperature dependent variable resistors. There are two types of thermistors, Positive Temperature Coefficient (PTC) and Negative Temperature Coefficient (NTC). When the temperature increases, PTC thermistor resistance will increase and NTC thermistor resistance will decrease. They exhibit the opposite response when the temperature decreases. Both types of thermistors are used in a variety of application areas. However, here the focus will be on using NTC thermistors to measure temperature in microcontroller based applications. Thermistor SpecificationsThe following NTC thermistor parameters can be found in the manufacturer's data sheet. ResistanceThis is the thermistor resistance at the temperature specified by the manufacturer, often 25°C.ToleranceIndicates how much the resistance can vary from the specified value. Usually expressed in percent (e.g. 1%, 10%, etc). For example, if the specified resistance at 25°C for a thermistor with 10% tolerance is 10,000 ohms then the measured resistance at that temperature can range from 9,000 ohms to 11000 ohms.B (or Beta) constantA value that represents the relationship between the re...
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Basic Knowledge of Thermocouple

Basic Knowledge of Thermocouple

MEI 07/02/2018 0
What is thermocouple?A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference. When two wires composed of dissimilar metals are joined at both ends and one of the ends is heated, there is a continuous current which flows in the thermoelectric circuit (the thermoelectric effect or Seebeck effect).Need for reference junction( cold junction):In thermocouples, voltage is developed due to flow of electric current. This current flow depends upon the difference in temperatures at the two ends of conducting wire. That is thermocouples always measure difference in temperatures and not absolute temperature.To measure the temperature of one junction, the other junction is kept at some reference temperature. As this is done by using ice bath, it is normally called at cold junction.Using ice bath for constant temperature is useful for laboratory calibration, but is not convenient for most measurement and control applications. Instead of ice bath, an effect of  cold junction is   added using a thermally sensitive device such as a thermistor or diode. This is also called as isothermal block. Special care is taken to minimize any tempera...
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Basic Knowledge of RTD

Basic Knowledge of RTD

MEI 07/02/2018 0
What is RTDRTD stands for Resistance Temperature Detector. RTDs are sometimes referred to generally as resistance thermometers. The American Society for Testing and Materials (ASTM) has defined the term resistance thermometer as follows:Resistance thermometer, n. - a temperature-measuring device composed of a resistance thermometer element, internal connecting wires, a protective shell with or without means for mounting a connection head, or connecting wire or other fittings, or both. [Vol. 14.03, E 344 - 02 § 3.1 (2007).]An RTD is a temperature sensor which measures temperature using the principle that the resistance of a metal changes with temperature. In practice, an electrical current is transmitted through a piece of metal (the RTD element or resistor) located in proximity to the area where temperature is to be measured. The resistance value of the RTD element is then measured by an instrument. This resistance value is then correlated to temperature based upon the known resistance characteristics of the RTD element.How do RTDs Work?RTDs work on a basic correlation between metals and temperature. As the temperature of a metal increases, the metal's resistance to the flow of ele...
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