Although temperature is one of the basic measurements for process control, system and even human health monitoring, the newest temperature sensors are anything but basic. To simplify their use in digital control systems, many of the newest sensors convert their analog measurement to a digital output using a high resolution analog to digital converter (ADC). Frequently, high functionality temperature sensors use the temperature sensitive characteristic of the transistor's base to emitter junction. However, for non-contact measurements, infrared (IR) technology is a likely choice, but added features require special techniques. Even the venerable thermocouple gets modernized with a multi-channel wireless node. Here is an example of each of these temperature-sensing techniques.
Addressable Digital Temperature Sensor
Allowing up to 27 addresses on one I2C communication bus as opposed to most competitors' eight addresses, Maxim Integrated Products' DS75LX digital temperature sensor has three dedicated address pins for configuring in three possible states: tied to VDD, ground or left floating. Since the pins can be left floating, the applications are significantly simplified. The DS75LX is calibrated for ±2.0C (max) accuracy rate for -25 to 100C and to ±3.0C (max) accuracy rate for temperatures of 55 to 125C. User-defined trip points and 9-, 10-, 11- or 12-bit digital temperature readings offer resolutions between 0.5C (9 bit) and 0.0625C (12 bit) allowing customized output hysteresis and threshold temperatures. If the data line is held longer than a predetermined amount of time, an optional bus-timeout function releases the data preventing any lockup issues that may occur on the two-wire bus.
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Medical Digital Temperature Sensor
Measuring human body temperatures behind the ear or on the forehead with infrared thermometers has become common occurrence in today's medically advanced society. Melexis' family of digital integrated temperature sensors offer digital, infrared, fully calibrated readings in a small and cost-effective unit. The MLX90614, introduced last year, offers custom signal conditioning chips integrated into one TO-39 metal can package. The MLX90614DAA, just introduced, offers a 3V product with the required ±0.1C accuracy in the 36 to 39C temperature range for medical measurements and a wide ambient operating range of 20 to 30C. To achieve this accuracy and high resolution, the unit has an integrated low noise amplifier, 17-bit ADC and digital signal processing (DSP) unit. The sensors are ideal for battery-operated devices since they have a sleep mode option with only µA level current.
http://rbi.ims.ca/5406-601
Wireless Thermocouple Node
MicroStrain's TC-LINK-6CH system is a six Channel 2.4 GHz 802.15.4 wireless thermocouple node with a cold junction compensation sensor and the option of a relative humidity sensor. The unit can transmit multiple nodes in real time to a single base station or has the capability to store up to 300,000 data points in its on-board memory. The TC-LINK-6CH's internal lithium ion battery can operate continuously for 10 months between recharges since the power circuit design uses only an average of 85 A. Supporting simultaneous data transmission from multiple nodes, including types J, K, R, S, T, E and B thermocouples, the unit has a 24-bit delta-sigma ADC for high resolution over a wide temperature range. The unit meets the IEEE 802.15.4 standards based communication protocol offering a wireless communications range of 70m line-of-sight with standard antennas or up to 280m line-of-sight with high-gain antennas. The nodes are ideal for concrete maturation, refrigeration, freezer performance monitoring, machine thermal management and more.
http://rbi.ims.ca/5406-602
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