Contactless Current Sensing for Industrial IoT
P. Garcha, B. Haroun, S. Ramaswamy, V. Schaffer, D. Buss, J. Lang, A. P. Chandrakasan
Sponsorship: Texas Instruments

The ability to sense current is crucial to many industrial applications including power line monitoring, motor controllers, battery fuel gauges, etc. We are developing smart connectors with current sensing abilities for use in the industrial internet of things (IoT). These connectors can be used for 1) power quality management: to measure real power, reactive power, and distortion, and 2) machine health monitoring applications for continuous monitoring, control, prevention, and diagnosis. At the system level, the smart connectors need to 1) measure AC, DC, and multiphase currents, 2) reject stray magnetic fields, and 3) detect impending connector failure. On the sensor level, they need to provide high measurement bandwidth (BW) and low power operation.
Current can be sensed directly by using a shunt resistor, but it leads to large power dissipation for measuring high current levels (10-100 A). Indirect/contactless sensing, which senses the magnetic field strength, is a better option as it offers galvanic isolation and the ability to operate safely in high voltage applications. Examples of contactless current sensors include Hall, magneto-resistive (MR), and fluxgate (FG) sensors. FG sensors with integrated magnetics offer higher sensitivity than Hall sensors (nT vs. µT) and higher linearity and lower offset hysteresis than MR sensors, making them a good choice for industrial current sensing.
The proposed system consists of a central processor and multiple low-power, high-BW FG sensors to make synchronous measurements (Figure 1). The measured data from all sensors is stored on the central processor, which runs preliminary analytics on the data before sending it to the cloud. Figure 2 shows the workings of a basic fluxgate sensor design. The proposed sensor makes use of various power saving techniques to reduce the energy per measurement, as well as digitally assisted analog circuits to push for high BW and BW scalability with duty cycling, from >100 kHz BW for machine health monitoring to <1 kHz for power quality management.
<Figure 1 here>	<Figure 2 here>	
Figure 1: Proposed contactless current sensing approach for smart connectors, including a central processor and multiple sensors to measure multi-phase currents and reject disturbances. The system can be wrapped around or plugged into the connectors.	Figure 2: Typical fluxgate sensor design, with two magnetic cores and three sets of coils: excitation, sense, and compensation. When excited, one core saturates before the other, and VSENSE µ`BIN-BCOMP`. Compensation provides feedback to improve linearity and measurement accuracy. 	
Further Reading
•	HARTING. 04. Industrial Connector Han e-Catalogue [Online]. Available: https://www.harting.com/sites/default/files/2018-02/DevCon_07_5_E_Kap04_Industrial-Connectors-Han.pdf, Feb. 2018.
•	M. F. Snoeij, V. Schaffer, S. Udayashankar, and M. V. Ivanov, “Integrated Fluxgate Magnetometer for use in Isolated Current Sensing,” IEEE J. Solid-State Circuits, vol. 51, no. 7, pp. 1684–1694, Jul. 2016.