Honeywell CC-TFB811 FIELDBUS INTERFACE IOTA, RED., 8-NETS P/n: 51306751-175

Instrumentation amplifiers are the appropriate choice to buffer the analog input module due to their high input impedance. DC errors from the INA will directly contribute to the final accuracy, therefore an instrumentation amplifier with low offset voltage (VOS), low VOS drift (VOS(DRIFT)), low gain error and gain nonlinearity, high common-mode rejection ratio (CMRR), and high power-supply rejection ratio (PSRR) will help keep the error contribution of the amplifier as low as possible. The INA826 was chosen because it achieves 240uV typical, VOS and 2.4 uV/°C typical, VOS(DRIFT) , +/-0.003% typical gain error and 1ppm typical gain nonlinearity. It also features a typical CMRR of 95 dB and a typical PSRR of 124dB. Wide input and output voltage ranges are also required in this application. INA826 has a wide supply range from 2.7V to 36V and rail- to -rail output stage which makes it suitable in this design

The four serial data signals required to communicate bi-directionally with the ADS1248 are serial communication signals SCLK, DIN, SDO, CS and start, DRDY. In order to maintain isolation from the host controller, these signals must be isolated through a digital isolator. The ISO7641 is chosen for the SPI communication with a 25Mbps digital isolator and ISO7221is cho

The ADS1248 is a 24-bit, delta-sigma (ΔΣ) ADC that offers a complete front-end solution for temperature detection applications. It comes from a product family of highly integrated precision data converters, featuring a low-noise programmable gain amplifier (PGA), a precision ΔΣ modulator, a digital filter, an internal oscillator, and two digitally controlled precision current sources (IDACs). It is a popular industry choice for precision temperature measurement applications.