How to apply self-interrogation and diagnostic functions to ensure the integrity of sensor data?
Sensors and Internet of Things (IoT) technologies are rapidly expanding into industry, commerce, and even consumer sectors. As this technology expands, there is an increasing need to ensure the integrity of data from related sensors and their front-end interface circuits.
When a single interface IC supports multiple sensors, the potential problem of data integrity becomes more serious, because a single IC problem may damage a set of readings. This may in turn lead to incorrect evaluation of the sensing situation, resulting in inappropriate or even dangerous system operation.
This article will introduce the various sources of soft-hard (transient) faults and inaccurate sensor readings in the sensor-to-processor signal chain. Then, this article will introduce from Analog Devices
Verify front end and ADC
Although external sensors and their leads are most likely to have problems, it is still critical to verify the performance of the front-end / conversion IC itself. Features that may exceed specifications or fail completely include:
Internal ADC voltage reference Programmable gain amplifier (PGA) to amplify the input signal to match the ADC range to achieve the highest resolution Low dropout voltage regulator (LDO) to provide the required sensor excitation IC's internal power rail
To test the analog part of the signal chain, the AD7124 calls a self-test based on hardware and firmware. A 20 millivolt (mV) signal is then generated, which can be internally transmitted to any of the four differential input channels and then digitized. This has multiple purposes: to verify the basic operation of the input channel multiplexer and ADC; you can also evaluate the PGA by changing the gain setting of the PGA and checking the resulting ADC reading.
ADC is also one of the root causes of potential problems. The AD7124 uses a perfect Σ-Δ converter architecture, which contains a 1-bit modulator and the necessary digital filters. Comprehensive testing of ADC performance uses both analog and digital technologies.
In the AD7124, if the modulator output contains 20 consecutive 1s or 0s, it means that one or the other rail of the modulator is saturated and an error flag is set. Similarly, the IC checks whether the ADC offset coefficient is between 0x7FFFF and 0xF80000 after starting the offset calibration. If the coefficient exceeds this range, another error flag will be set. Finally, during full-scale calibration, any overflow of the digital filter will set another error flag.
Internal and external power supplies and power rails are also potential sources of problems. Many sensors require a small amount of excitation power, and this is usually provided by a small, low-noise LDO in the analog front-end IC.
The AD7124 checks its LDO output in two ways. First, the output of the LDO can be routed internally to the ADC and compared with the expected value. Second, a hardware comparator independent of the ADC continuously monitors the change of the LDO relative to the IC reference value. If it is below the preset threshold, an error flag will be set. Therefore, the LDO can be evaluated during initialization, or it can be continuously evaluated without continuously consuming processor resources.
To further convince you, you can (to a certain extent) check the test circuit used to monitor the power supply by grounding the input of the test circuit (nominal 0 volts) and then checking the digital reading. The AD7124 further ensures data integrity by checking that the required 0.1 microfarad (µF) decoupling capacitor is present and connected. The method is to instruct the AD7124 to physically disconnect the decoupling capacitor through its internal switch, and then check the LDO output. If the LDO voltage drops, the decoupling capacitor is not energized. Similarly, this will also set the error flag.
Of course, each IC has the highest temperature rating, and exceeding this value will exceed the specification and may even cause a failure immediately. Therefore, the AD7124 has a built-in sensor that can provide chip temperature readings at any time, with a typical accuracy of ± 0.5 ° C.
To sum up
Many key decisions are made by advanced algorithms embedded in the system's processor, and this decision-making method is now improved in many cases by artificial intelligence (AI). The raw data on which these algorithms operate, draw conclusions, and take action must have a high degree of integrity, which is more important than ever. ICs such as the AD7124 can significantly increase the credibility of the data, ensuring that every link in the signal chain (from leads and sensor interfaces to its own performance and functionality) operates as expected and is not damaged.
If you want to know more, our website has product specifications for sensor, you can go to ALLICDATA ELECTRONICS LIMITED to get more information