Advancement in Temperature Sensors

The devices which have dense circuits dissipate lot of power. These devices need Temperature sensor to control battery charging and to prevent damage to microprocessor and other expensive components.

Such devices generally use a Fan to control the temperature. In order to increase the battery life Fan is operated only when it is necessary. Temperature sensors are needed here to know the critical temperatures and control the Fan operation.

Temperature sensors are used in monitoring of Portable equipments temperature, CPU temperature, Battery temperature and ambient temperature. They are also used in process control and instrumentation applications.

Since in most cases the output of temperature sensors are non linear, they are first conditioned and amplified before they are processed.

In past, complex circuits were needed to correct non linearity of temperature sensors. Over this, these circuits needed manual calibrations and precision resistors were required to achieve the desired accuracy. Now days, high resolution ADCs are used to digitize the sensor outputs directly.

There are several types of Temperature sensors available. Resistance Temperature Devices (RTD) is accurate and fairly linear. They have range of -200 Deg C to +850 Deg C. Thermistors have highest sensitivity but are most non linear. They work in the range of 0 to 100 Deg C. Semiconductor temperature sensors are most advanced. They are highly accurate and linear. They work in the range of -55 to 150 Deg C. Internal amplifiers can scale the output to convenient values, such as 10mV/°C.

The bandgap temperature sensors are used as the basis for variety of IC temperature sensors to generate either current or voltage outputs.

In some cases where the temperature sensor output is required to be ratio metric with its supply voltage the Ratio metric voltage output sensors are used.

Digital output temperature sensors are used especially in remote applications. Output of sensor is digitized by a sigma-delta modulator. The output of modulator is encoded in a serial digital output signal with a mark-space ratio format that is decoded by microprocessor into either degrees centigrade or degrees Fahrenheit. As this modulation technique is clock independent, it avoids error sources common to other modulation techniques.

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