Maxim App Note: 4542
Abstract: This circuit is a simple and economical interface for remote IC thermal sensors. The temperature sensor (MAX6576), an absolute temperature-to-period converter that integrates the sensor with the necessary signal electronics, connects to the receiver (a MAX9140 comparator) using a twisted-pair cable that carries power to and signals from the sensor.
A similar version of this article appeared in the November 5, 2007 issue of ED magazine.
The Note begins:
The best choice for midrange, low-to-medium-accuracy temperature measurements (considering size, cost, performance, and ease of use) is an IC temperature sensor???assuming the circuits to be interfaced with the sensor reside on the same board or in the same box. Most IC temperature sensors are designed for applications in which the circuits to which they connect are nearby, so the inclusion of sensing, digitizing, and signal-processing functions in a single IC greatly simplifies the design of such sensors and the data-acquisition interface.
Some applications, however, require the acquisition of temperature data from locations quite remote from the power supply and data-processing electronics. You must exercise extra care with such systems, because any deterioration in the signal from the remote sensor can degrade the measurement quality.
Choosing to digitize and process the signal at the point of measurement (near the sensor) greatly reduces the problem of signal integrity, but that approach also complicates the interconnection and raises the problem of supplying power to the circuit. Either design option (signal processing remote or at the sensor) requires cabling that is complex or expensive or both.
The circuit of Figure 1 provides a simple and economical interface for remote IC thermal sensors. The temperature sensor (MAX6576) is an absolute temperature-to-period converter that integrates the sensor with the necessary signal electronics. It connects to the receiver (a simple comparator) using a twisted-pair cable that simultaneously carries power to the sensor and signals from the sensor…
Read the entire App Note online at www.maxim-ic.com/app-notes/index.mvp/id/4542