A Guide To Working With Temperature Sensors
It is possible to make sure the advanced systems available today, no matter how small they may be operate in a safe thermal zone by implementing real time temperature monitoring with dedicated temperature sensors. It is usually possible to monitor the internal and external hot spots of the system in question with a very high accuracy. All this is done by making use of low-cost and easy to use sensor ICs which allow the designers to make modules to measure chip temperatures and also to squeeze the maximum performance from such systems.
Temperature Sensors – The Need Of The Hour – Almost all the systems are affected by temperature. They may be biological, chemical, physical, mechanical or even electronic systems. Temperature remains the most frequently measured environmental quality. And rightly so, most of these systems are temperature sensitive and one must take proper care of them by monitoring them as closely as possible.
The way such systems are designed, their circuits could be damaged if the temperature exceeds the specified operating temperature that is normally provided when you purchase the device. In several smart systems which posses temperature monitoring facilities auto shutdown can be initiated when it crosses the temperature threshold.
The different types of temperature sensing techniques used currently are thermocouples, thermistors, and even integrated circuits. Any one of these can be implemented depending several factors like accuracy, cost, the required temperature range and general feature list as explained in slightly more detail as this article progresses.
Thermocouples – A thermocouple is nothing more than two dissimilar metals that are joined together at one end and produce a small voltage when exposed the certain temperature. The way this works is that the thermoelectric voltage is actually the sum of all the voltage differences along the wire from end to end which results from the temperature difference from one end of the wire to the other.
The good thing about thermocouples is their low thermal mass and their wide operating temperature range. For example they can be extended up to 1700 degrees. On the other hand their sensitivity is rather small. In addition to which a low offset amplifier is required to produce a usable output voltage.
Thermistors – Thermistors can be used as temperature sensors since they behave like temperature sensitive electrical resistors. They are composed of semiconductor material and are generally of two different types, like negative temperature coefficient and positive temperature coefficient. The negative temperature coefficient type are mainly used in temperature sensing scenarios while the positive temperature coefficient are used in electric current control.
The thermistor is designed such that it exhibits a change in the electrical resistance with the change in temperature. The resistance is measured by passing a small though specific, direct current through it. The voltage drop is measured then measured. The negative temperature coefficient type the negative coefficient can be quite large per degrees centigrade. This allows the thermistor to register minute changes in temperature which is not possible with the thermocouple circuit.
There are many different kinds of thermistors available. The low cost ones are use top perform simple measurements and are of low precision thus perform on low end systems. Then there are the ones that function from -100 to 550 degrees centigrade
The performance of thermistors tends to degrade due to the process of self heating. A correction is thus required in the form of linearization.
Sensor ICs – Remote Temperature Sensor ICs are very popular and are available in a wide range. They are capable of simplifying the broadest possible temperature monitoring challenges. It can operate in the range of -55 to 150 degrees centigrade. Since the temperature sensor is also an integrated circuit no additional circuit is required for secondary processes like linearisation for example. It is all included in one package. It is the ideal solution for microprocessor based systems due to the it’s versatility.
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