A high performance analogue front end combines low noise and low offset buffered ADCs with all the necessary excitation and control circuits for each sensor. Measurements are performed under the control of a digital engine combining all the algorithms and linearisation required for each. The LTC2983 provides a multiplexed high precision interface to virtually any sensor. It precisely measures absolute microvolt level signals from thermocouples and ratiometric resistance measurements from RTDs and thermistors, linearises the results and outputs the results in °C or °F. Up to twenty analogue inputs are available. The SPI interface works with virtually any digital system and a comprehensive software support system with drop-down menus allows easy customising of the IC.
LTC2983 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. It works with ground-referenced sensors without the need for amplifiers, negative supplies, or level shift circuitry. Signals are simultaneously digitised with three, high accuracy, 24-bit ΔΣ ADCs using an internal 10ppm/°C reference. Automatic thermocouple cold junction compensation can be done using any type of external sensor. Included on the chip are linearisation algorithms for all common sensor types. Custom sensors can be linearised 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 device comes in commercial and industrial versions, supporting operating temperature ranges from 0°C to 70°C and –40°C to 85°C respectively. In a 7 x 7mm LQFP-48 package, pricing starts at $20.66 (1,000).
Linear Technology; www.linear.com/product/LTC2983
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