A chip called the LTC2983 directly digitizes RTDs, thermocouples, thermistors and external diodes with 0.1°C accuracy and 0.001°C resolution.
The device combines low-noise and low-offset-buffered ADCs with excitation and control circuits for each type of sensor. The chip precisely measures absolute microvolt-level signals from thermocouples and ratiometric resistance measurements from RTDs and thermistors, linearizes the results and outputs the results in °C or °F. Up to twenty analog inputs are available and digitized measurements can be output in Centigrade or Fahrenheit. A serial peripheral interface and a comprehensive software support system with drop-down menus lets developers customize the chip.
The chip interfaces with a wide variety of temperature sensors, including type B, E, J, K, N, S, R, T thermocouples, 2,3, or 4-wire RTDs, 2.25 kΩ to 30 kΩ thermistors and temperature sensing diodes. The LTC2983 works with ground referenced sensors without the need for amplifiers, negative supplies, or level shift circuitry. Signals are simultaneously digitized with three, high accuracy, 24-bit Δ∑ ADCs using an internal 10 ppm/°C reference.
Automatic thermocouple cold junction compensation can take place using any type of external sensor. Included on the chip are linearization algorithms for all common sensor types. Custom sensors can be linearized with custom coefficients programmed into the chip. Dual programmable excitation current sources feature current reversal and current ranging to improve accuracy and reduce noise. To ensure resistive measurements are accurate, current reversal eliminates thermocouple effects in the resistive sensor. Sensor specific fault detection alerts the user of short circuits, open circuits, over temperature, under temperature, and ADC overranging.
The LTC2983 is offered in commercial and industrial versions, supporting operating temperature ranges from 0°C to 70°C and –40°C to 85°C respectively. The chip comes in a RoHS compliant, 7×7-mm LQFP-48 package. Pricing starts at $19.49 each in 1,000 piece quantities.
Linear Technology Corp., 1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900, FAX: (408) 434-0507, www.linear.com/product/LTC2983.