In power-down mode, the complete ADC along with its auxiliary functions are powered down so that the AD7124-4/AD7124-8 consume 1 μA typical. The current consumed in low power mode is only 255 μA and in full power mode is 930 μA. Several options of the on-chip digital filtering and three integrated power modes, where the current consumption, range of output data rates, settling time, and rms noise are optimized, provide application flexibility. Functions, including programmable excitation current sources and a programmable gain amplifier (PGA), excite and gain the RTD, respectively, which allows direct interfacing with the sensor and simplifies the design while reducing cost and power consumption. The AD7124-4/AD7124-8 integrate several important system building blocks required to support RTD measurements. These settings show that the system accuracy is significantly better than the sensor accuracy. The typical peak to peak resolution of the system is 0.0043☌ (17.9 bits) for full power mode, sinc4 filter selected, at an output data rate of 50 SPS, and 0.0092☌ (16.8 bits) for low power mode, post filter selected, at an output data rate of 25 SPS. The AD7124-4/AD7124-8 can achieve high resolution, low nonlinearity, and low noise performance as well as high 50 Hz and 60 Hz rejection, suitable for industrial RTD systems. This circuit also has provision for Pt1000 RTDs that are useful in low power applications. This circuit note uses a Class B Pt100 RTD sensor with an accuracy of ☐.3☌ at 0☌ but it can support other classes such as Class A, Class AA, 1/3 DIN, or 1/10 DIN that are higher accuracy RTDs. 2-Wire, 3-Wire, or 4-Wire RTD Measurement Configuration The circuit shown in Figure 1 is an integrated 2-wire, 3-wire, or 4-wire resistance temperature detector (RTD) system based on the AD7124-4/ AD7124-8 low power, low noise, 24-bit Σ-Δ analog-to-digital converter (ADC) optimized for high precision measurement applications. The industry’s lowest power and smallest footprint HART-compliant IC modem the ADuM1441, which provides ultralow power serial peripheral interface (SPI) isolation the ADG5433ĬMOS switch and the ADP162 low power, 3.3 V regulator in Loop powered digital-to-analog converter (DAC) the AD5700, The circuit also includes the AD5421, a 16-bit, 4 mA to 20 mA, The circuit uses the AD7124-4, an ultralow power, precisionĢ4-bit, Σ-Δ analog-to-digital converter (ADC), which includesĪll the features needed for temperature and pressure systems. Transmission of process variables, which are necessary inĪpplications such as temperature and pressure control. The HART interface allowsįeatures such as remote calibration, fault interrogation, and Keyed (FSK) signal is modulated on top of the standard 4 mA to 20 mA analog current signal. HART is a digital 2-way communication in which a 1 mA peak-to-peak frequency shift The instrument communicates via aĤ mA to 20 mA analog output and a highway addressable Such as temperature (Pt100, Pt1000, and thermocouple) or bridge pressure sensors. The circuit shown in Figure 1 is an isolated smart industrial field instrument that interfaces to many types of analog sensors Because thermocouples are so basic, they have several advantages: they can measure extreme temperatures of –270☌ to +1800☌, are robust, can be very small, can have a very fast response time, and have no self-heating. They are inexpensive, interchangeable, and usually supplied with standard connectors. In contrast to most other methods of temperature measurement, thermocouples are self-powered and require no external form of excitation. This reference point sensor is also known as the cold junction compensation point. Therefore, an additional temperature sensor is required to measure the reference point temperature and is usually a silicon-based sensor, RTD, or thermistor. It produces a temperature-dependent voltage as a result of the thermoelectric effect, and this voltage is proportional to the difference in temperature between the measurement junction and the reference point. A thermocouple is an electrical device consisting of two dissimilar metal wires forming an electrical measurement junction at one end and a two-terminal connection at the other end called the reference point.
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