Showing papers on "Current sensor published in 2016"

Sensor Fault Detection, Isolation, and Estimation in Lithium-Ion Batteries

Abstract: In battery management systems (BMSs), real-time diagnosis of sensor faults is critical for ensuring the safety and reliability of the battery. For example, a current sensor fault leads to erroneous estimates of state of charge and other parameters, which in turn affects the control actions in the BMS. A temperature sensor fault may lead to ineffective thermal management. In this brief, a model-based diagnostic scheme is presented that uses sliding mode observers designed based on the electrical and thermal dynamics of the battery. It is analytically shown how the extraction of the equivalent output error injection signals on the sliding manifolds enables the detection, the isolation, as well as the estimation of the temperature, voltage, and current sensor faults. This brief includes simulation and experimental studies to demonstrate and evaluate the effectiveness of the proposed scheme. Discussions are also included on the effects of uncertainty and on threshold design.

Gate driver design for 1.7kV SiC MOSFET module with Rogowski current sensor for shortcircuit protection

Abstract: This paper shows a gate driver design for 1.7 kV SiC MOSFET module as well a Rogowski-coil based current sensor for effective shortcircuit protection. The design begins with the power architecture selection for better common-mode noise immunity as the driver is subjected to high dv/dt due to the very high switching speed of the SiC MOSFET modules. The selection of the most appropriate gate driver IC is made to ensure the best performance and full functionalities of the driver, followed by the circuitry designs of paralleled external current booster, Soft Turn-Off, and Miller Clamp. In addition to desaturation, a high bandwidth PCB-based Rogowski current sensor is proposed to serve as a more effective method for the shortcircuit protection for the high-cost SiC MOSFET modules.

Online Sensorless Position Estimation for Switched Reluctance Motors Using One Current Sensor

Abstract: This paper proposes an online sensorless rotor position estimation technique for switched reluctance motors (SRMs) using just one current sensor. It is achieved by first decoupling the excitation current from the bus current. Two phase-shifted pulse width modulation signals are injected into the relevant lower transistors in the asymmetrical half-bridge converter for short intervals during each current fundamental cycle. Analog-to-digital converters are triggered in the pause middles of the dual pulse to separate the bus current for excitation current recognition. Next, the rotor position is estimated from the excitation current, by a current-rise-time method in the current-chopping-control mode in a low-speed operation and a current-gradient method in the voltage-pulse-control mode in a high-speed operation. The proposed scheme requires only a bus current sensor and a minor change to the converter circuit, without a need for individual phase current sensors or additional detection devices, achieving a more compact and cost-effective drive. The performance of the sensorless SRM drive is fully investigated. The simulation and experiments on a 750-W three-phase 12/8-pole SRM are carried out to verify the effectiveness of the proposed scheme.

Fault diagnosis scheme for open-circuit faults in switched reluctance motor drives using fast Fourier transform algorithm with bus current detection

Abstract: Reliability of power converters is of crucial importance in switched reluctance motor drives used for safety-critical applications. Open-circuit faults in power converters will cause the motor to run in unbalanced states, and if left untreated, they will lead to damage to the motor and power modules, and even cause a catastrophic failure of the whole drive system. This study is focused on using a single current sensor to detect open-circuit faults accurately. An asymmetrical half-bridge converter is considered in this study and the faults of single-phase open and two-phase open are analysed. Three different bus positions are defined. On the basis of a fast Fourier transform algorithm with Blackman window interpolation, the bus current spectrums before and after open-circuit faults are analysed in details. Their fault characteristics are extracted accurately by the normalisations of the phase fundamental frequency component and double phase fundamental frequency component, and the fault characteristics of the three bus detection schemes are also compared. The open-circuit faults can be located by finding the relationship between the bus current and rotor position. The effectiveness of the proposed diagnosis method is validated by the simulation results and experimental tests.

Integrated switch current sensor for shortcircuit protection and current control of 1.7-kV SiC MOSFET modules

Abstract: This paper presents design and implementations of a switch current sensor based on Rogowski coils. The current sensor is designed to address the issue of using desaturation circuit to protect the SiC MOSFET during shortcircuit. Specifications are given to meet the application requirement for SiC MOSFETs. It is also designed for high accuracy and high bandwidth for converter current control. PCB-based winding and shielding layout is proposed to minimize the noises caused by the high dv/dt at switching. The coil on PCB are modeled by impedance measurement, thus the bandwidth of coil is calculated. At the end, various test results are demonstrated to validate the great performance of the switch current sensor.

Wavelet Packet Decomposition-Based Fault Diagnosis Scheme for SRM Drives With a Single Current Sensor

Abstract: Power converters are a key, but vulnerable component in switched reluctance motor (SRM) drives. In this paper, a new fault diagnosis scheme for SRM converters is proposed based on the wavelet packet decomposition (WPD) with a dc-link current sensor. Open- and short-circuit faults of the power switches in an asymmetrical half-bridge converter are analyzed in details. In order to obtain the fault signature from the phase currents, two pulse-width modulation signals with phase shift are injected into the lower-switches of the converter to extract the excitation current, and the WPD algorithm is then applied to the detected currents for fault diagnosis. Moreover, a discrete degree of the wavelet packet node energy is chosen as the fault coefficient. The converter faults can be diagnosed and located directly by determining the changes in the discrete degree from the detected currents. The proposed scheme requires only one current sensor in the dc link, while conventional methods need one sensor for each phase or additional detection circuits. The experimental results on a 750-W three-phase SRM are presented to confirm the effectiveness of the proposed fault diagnosis scheme.

Current sensor fault detection and isolation method for PMSM drives, using average normalised currents

Abstract: A new approach for current sensor fault detection and isolation (FDI) for permanent magnet synchronous motor (PMSM) drives is presented. Contrary to the classical approaches for sensors fault diagnosis, based on residual generation through observers or parity equations, the proposed technique uses the average normalised machine-phase currents. The main advantages of this approach are that it does not need any information about the PMSM or inverter models, and it involves low tuning efforts, that make it suitable for real-time implementation with good reliability. The good performance and the robustness of the proposed FDI approach are illustrated through experimental results.

Low-cost direct instantaneous torque control for switched reluctance motors with bus current detection under soft-chopping mode

Abstract: This study proposed a low-cost torque distribution function (TSF)-based direct instantaneous torque control (DITC) technique for switched reluctance motors (SRMs) by bus current detection under soft-chopping mode. A three-phase 12/8-pole prototype SRM is employed to analyse the phase currents and operation states, and a new converter connection with bus current sensor placement strategy is presented to replace the phase current sensors in each phase leg. Considering that the conventional bus current contains both the chopping current and demagnetisation current, the current sensor is placed in a new bus to remove all the needless demagnetisation currents. To obtain the chopping current information from the bus current for DITC implementation, pulse-width modulation signals with extremely short turn-off time are injected into the lower transistors to insert the chopping current detection states for brief intervals during each fundamental frequency cycle. The DITC scheme is implemented directly on the detected chopping currents from bus current based on a sinusoidal TSF. The proposed DITC system is more compact and low cost by using just a bus current sensor. The effectiveness of the proposed technique is verified by the simulation and experimental results.

A Method to Simultaneously Detect the Current Sensor Fault and Estimate the State of Energy for Batteries in Electric Vehicles.

Abstract: Recently, State of energy (SOE) has become one of the most fundamental parameters for battery management systems in electric vehicles. However, current information is critical in SOE estimation and current sensor is usually utilized to obtain the latest current information. However, if the current sensor fails, the SOE estimation may be confronted with large error. Therefore, this paper attempts to make the following contributions: Current sensor fault detection and SOE estimation method is realized simultaneously. Through using the proportional integral observer (PIO) based method, the current sensor fault could be accurately estimated. By taking advantage of the accurate estimated current sensor fault, the influence caused by the current sensor fault can be eliminated and compensated. As a result, the results of the SOE estimation will be influenced little by the fault. In addition, the simulation and experimental workbench is established to verify the proposed method. The results indicate that the current sensor fault can be estimated accurately. Simultaneously, the SOE can also be estimated accurately and the estimation error is influenced little by the fault. The maximum SOE estimation error is less than 2%, even though the large current error caused by the current sensor fault still exists.

State-of-charge and state-of-health estimation with state constraints and current sensor bias correction for electrified powertrain vehicle batteries

Abstract: Pragmatic approaches are proposed to enhance battery state estimation using Kalman filter (KF) and extended KF. Notable novelties introduced include: the use of state/parameter constraints, asymmetric equivalent circuit model behaviour, inclusion of nominal models, and current sensor measurement bias estimation and compensation. The so-called delta parameters are estimated to handle cell variations, aging, and online deviation of parameters. Strategic simplifications that enable the use of traditional KF algorithm are described. Unique filter structures are presented for state-of-charge and state-of-health estimation, the latter focuses on capacity and impedance estimation. The performance of the proposed approaches is demonstrated on experimental drive-cycle data designed for electric vehicle (EV) and hybrid EV applications.

A Sensorless Implementation of the Parabolic Current Control for Single-Phase Stand-Alone Inverters

Abstract: Parabolic current control is an attractive current control method with fast transient response and constant switching frequency. Due to the good dynamics of the parabolic current control, it can be employed in voltage source inverters to improve the system performance such as minimizing the distortion of current waveforms or voltage waveforms. To implement the parabolic current control, a current sensor is required, associated with the current conditioning circuit and parabolic carrier generators. Since the parabolic current control is based on the real-time information of the inductor current, any phase delay or propagation delay of the sensor itself and the conditioning circuitry, or limited resolution of parabolic carrier generators, could impact the current control performance. Since the parabolic current control compares analog signals to generate the required control signals, noise from the control board impacts the control precision as well. This paper will explore solutions to these problems. First, the inductor current of the voltage source inverter is analyzed and the parabolic current control strategy is studied, then a sensorless parabolic current control method is proposed. The new sensorless parabolic control method utilizes a current emulator to rebuild the inductor current on a microcontroller. To avoid a dc offset on the ac-side output voltage caused by the current emulator, an additional control loop in the current emulator is added. The effectiveness of the proposed methods is experimentally verified by the use of an H-bridge voltage source inverter.

An Active Life Extension Strategy for Thermally Aged Power Switches Based on the Pulse-Width Adjustment Method in Interleaved Converters

Abstract: The research on noninvasive incipient fault diagnosis of power converters is very critical to avoid strenuous periodic checkups and costly interruptions. In many of the research studies, on-state resistance of power MOSFETs is identified as the fault precursor, and suggested to be monitored online for prognosis. In this paper, a condition monitoring algorithm is proposed for power MOSFETs of interleaved converters and integrated with the conventional current loops. The proposed technique utilizes on-state resistance information of the switches to adjust the current reference of each interleaving leg. In addition, a pulse-width adjustment method is proposed to avoid one current sensor and current-control loop. With the proposed scheme, the thermal stress on the aged device can be reduced, and the overall lifetime of the converter can be extended. The proposed approach is verified on two-leg interleaved converters both in simulation and experimentally.

Current sensing using circularly birefringent twisted solid-core photonic crystal fiber.

Abstract: Continuously twisted solid-core photonic crystal fiber (PCF) exhibits pure circular birefringence (optical activity), making it ideal for current sensors based on the Faraday effect. By numerical analysis, we identify the PCF geometry for which the circular birefringence (which scales linearly with twist rate) is a maximum. For silica-air PCF, this occurs at a shape parameter (diameter-to-spacing ratio of the hollow channels) of 0.37 and a scale parameter (spacing-to-wavelength) of 1.51. This result is confirmed experimentally by testing a range of different structures. To demonstrate the effectiveness of twisted PCF as a current sensor, a length of fiber is placed on the axis of a 7.6 cm long solenoid, and the Faraday rotation is measured at different values of dc current. The system is then used to chart the wavelength dependence of the Verdet constant.

Kinetic inductance parametric up-converter

Abstract: We describe a novel class of devices based on the nonlinearity of the kinetic inductance of a superconducting thin film. By placing a current-dependent inductance in a microwave resonator, small currents can be measured through their effect on the resonator’s frequency. By using a high-resistivity material for the film and nanowires as kinetic inductors, we can achieve a large coefficient of nonlinearity to improve device sensitivity. We demonstrate a current sensitivity of 8pA/√Hz, making this device useful for transition-edge sensor (TES) readout and other cutting-edge applications. An advantage of these devices is their natural ability to be multiplexed in the frequency domain, enabling large detector arrays for TES-based instruments. A traveling-wave version of the device, consisting of a thin-film microwave transmission line, is also sensitive to small currents as they change the phase length of the line due to their effect on its inductance. We demonstrate a current sensitivity of 5pA/√Hz for this version of the device, making it also suitable for TES readout as well as other current-detection applications. It has the advantage of multi-GHz bandwidth and greater dynamic range, offering a different approach to the resonator version of the device.

Near-Optimal Sensor Scheduling for Batch State Estimation: Complexity, Algorithms, and Limits

Abstract: In this paper, we focus on batch state estimation for linear systems. This problem is important in applications such as environmental field estimation, robotic navigation, and target tracking. Its difficulty lies on that limited operational resources among the sensors, e.g., shared communication bandwidth or battery power, constrain the number of sensors that can be active at each measurement step. As a result, sensor scheduling algorithms must be employed. Notwithstanding, current sensor scheduling algorithms for batch state estimation scale poorly with the system size and the time horizon. In addition, current sensor scheduling algorithms for Kalman filtering, although they scale better, provide no performance guarantees or approximation bounds for the minimization of the batch state estimation error. In this paper, one of our main contributions is to provide an algorithm that enjoys both the estimation accuracy of the batch state scheduling algorithms and the low time complexity of the Kalman filtering scheduling algorithms. In particular: 1) our algorithm is near-optimal: it achieves a solution up to a multiplicative factor 1/2 from the optimal solution, and this factor is close to the best approximation factor 1/e one can achieve in polynomial time for this problem; 2) our algorithm has (polynomial) time complexity that is not only lower than that of the current algorithms for batch state estimation; it is also lower than, or similar to, that of the current algorithms for Kalman filtering. We achieve these results by proving two properties for our batch state estimation error metric, which quantifies the square error of the minimum variance linear estimator of the batch state vector: a) it is supermodular in the choice of the sensors; b) it has a sparsity pattern (it involves matrices that are block tri-diagonal) that facilitates its evaluation at each sensor set.

Load-current-based current sensor fault diagnosis and tolerant control scheme for traction inverters

Abstract: Based on analysing the load currents, a current sensor fault diagnosis method for three-phase voltage source inverters in high-speed railway electrical traction drive system is presented. Then, a fault-tolerant algorithm is applied to reconstruct the three-phase currents. This fault diagnosis and tolerant control approach is an extension of the normalised average currents method, which requires no additional hardware and permits much more robust diagnostics. Experimental results confirm the effectiveness and accuracy of the proposed algorithm. It is shown that such diagnosis method can locate the faulty sensor, identify the fault modes, and recover the drive system in a fundamental period which is important to avoid catastrophic consequences.

Self-Contained Wireless Hall Current Sensor Applied for Two-Wire Zip-Cords

Abstract: A self-contained wireless current sensor applied for two-wire zip-cords is proposed in this paper, which consists of a Hall sensor, a wireless module, and an energy harvester along with the power management circuit. The energy harvester is constructed from a current transformer, where an EE-type magnetic core with two arms is specially designed by making a slit in one arm to produce unsymmetric field distributions: the field with low flux density is used for sensing and that with higher flux density for energy harvesting. In the energy scavenging operation, the sensor can generate 4.3 $\mu \text{W}$ with a 217 $\Omega $ load resistor under 1 A zip-cord carrying current and supply power for the off-shelf Zig-bee nRF24LE1 wireless module to send one data for a time duration of about 5 min. In current-sensing operation, the sensor exhibits a sensitivity of 0.85 mV/A with a sensed current ranging from 1 A to 130 A.

An Efficiency-Enhanced Hybrid Supply Modulator With Single-Capacitor Current-Integration Control

Abstract: This paper presents a high-efficiency wideband hybrid supply modulator (HSM). We show that proper control of the average current from the class-AB linear amplifier (LA) and proper selection of the inductor value are essential to efficiency optimization. In line with the above criteria, a single-capacitor current-integration (SCCI) control method is proposed. Current integration is achieved by using a single capacitor, circumventing the need of the high-speed full-range current sensor required for conventional HSMs and reducing the design complexity greatly. The ripple current of the LA is controlled indirectly, and enhanced efficiency is achieved by enforcing the average output current from the LA to be around zero. A wideband LA is proposed to suppress the output voltage ripple. A proof-of-concept design using an inductor with an optimized value of 100 nH is fabricated in 130 nm CMOS technology. It switches at a peak frequency of 50 MHz, achieves up to 8% efficiency improvement when compared to recent works, and is able to track a $0.8\;{\text{V}}_\text{pp}$ sinusoidal signal with high fidelity up to 10 MHz. The measured output voltage ripple is reduced to below 8 mV. The peak conversion efficiency is 88.3% at the maximum output power of 23 dBm.

Switching power supply for RF power amplifiers

Abstract: The present disclosure describes a synchronized switching power supply for a radio frequency (RF) power amplifier. In some aspects, a synchronized power supply circuit comprises a first switch connected between a power rail and a first terminal of an inductor that is connected to an output of the circuit via its second terminal. The circuit also includes a second switch connected between a ground rail and the first terminal of the inductor, and respective gate drivers for the first and second switches. An amplifier of the circuit is connected to the power rail and has an output connected to the output of the circuit. A current sensor is connected between the output of the amplifier and the output of the circuit, with an output of the current sensor being connected to an input of a comparator. A delay circuit is connected between an output of the comparator and the first and second gate drivers, and may synchronize the power supply circuit.

A Novel Low-Cost Multicoil-Based Smart Current Sensor for Three-Phase Currents Sensing of Overhead Conductors

Abstract: This paper proposes a novel technique and algorithm for the simultaneous sensing of three-phase currents based on multiple air-core coils. The basic principle for the current measurement in one conductor using one and two air-core coils is derived, and a means of self-calibration is determined. In order to measure the three-phase currents in parallel overhead lines, a novel smart current sensor has been developed, consisting of four air-core coils located in close proximity to the conductors. Algorithms are derived, simulations and extensive experimental verification is conducted, and a first prototype is fabricated and tested. Measurement errors introduced by variations in sensor orientation and the effect of adjacent conductors are both analyzed. The proposed technique and algorithm promise a novel smart current sensor for three-phase currents, simultaneously sensing the overhead conductors, which are low cost, small in size, easy to deploy extensively, do not require clamping around the utility conductor, and have the capability to self-calibrate. Integrated with the wireless-sensor network technique, these smart sensors can be widely applied in dynamic state estimation, monitoring, and optimal operation of the distribution network, and will become an integral part of energy-management systems of future power distribution networks.

Power storage system

Abstract: PROBLEM TO BE SOLVED: To suppress the decrease in charging amount of an auxiliary device battery, accompanying an offset learning process of a current sensor during the rise in temperature.SOLUTION: A power storage system according to the present invention comprises: a heater operable to raise the temperature of a power storage device; a first DC/DC converter operable to output a power from the power storage device or from an external power source for charging the power storage device to an auxiliary device battery and the heater; a second DC/DC converter of which the output side is connected in parallel with the auxiliary device battery and the heater, and the input side is connected to the external power source or a solar panel provided on a vehicle; a current sensor operable to detect a charge/discharge current of the power storage device; and a controller operable to stop the first DC/DC converter from working and perform an offset learning process of the current sensor. When performing the offset learning process during power supply to the heater through the first DC/DC converter, the controller controls so as to operate the second DC/DC converter to supply a power output from the external power source or solar panel to the auxiliary device battery and the heater.SELECTED DRAWING: Figure 2

An Energy Saving System for a Beam Pumping Unit

Abstract: Beam pumping units are widely used in the oil production industry, but the energy efficiency of this artificial lift machinery is generally low, especially for the low-production well and high-production well in the later stage. There are a number of ways for energy savings in pumping units, with the periodic adjustment of stroke speed and rectification of balance deviation being two important methods. In the paper, an energy saving system for a beam pumping unit (ESS-BPU) based on the Internet of Things (IoT) was proposed. A total of four types of sensors, including load sensor, angle sensor, voltage sensor, and current sensor, were used to detect the operating conditions of the pumping unit. Data from these sensors was fed into a controller installed in an oilfield to adjust the stroke speed automatically and estimate the degree of balance in real-time. Additionally, remote supervision could be fulfilled using a browser on a computer or smartphone. Furthermore, the data from a practical application was recorded and analyzed, and it can be seen that ESS-BPU is helpful in reducing energy loss caused by unnecessarily high stroke speed and a poor degree of balance.

Phase Current-Balance Control Using DC-Link Current Sensor for Multiphase Converters With Discontinuous Current Mode Considered

Abstract: This paper presents a new phase current-balance control method of unbalanced phase currents in multiphase converters. The phase current reconstruction process, in which the sampled dc-link current from a dc-link current sensor is used to reconstruct the phase currents, is comprehensively investigated, taking account of both the region of duty ratio and the operating mode of the continuous current mode (CCM) and discontinuous current mode (DCM). DCM operation reveals that the phase current reconstruction cannot coincide with the average value of the respective phase current. Eventually, it is confirmed that this proposed balance control based on a circular chain control makes it possible to establish an exact current sharing among the phase currents all over the operating condition including the DCM. The actual phase currents do not show any distorted waveforms due to the multisamplings of dc-link current that do not provoke any extra switching of the converter switches at all. The validity and effectiveness of the proposed phase current-balance control are illustrated through the experimental results.

An Optical Fiber Sensor and Its Application in UAVs for Current Measurements.

Abstract: In this paper, we propose and experimentally investigate an optical sensor based on a novel combination of a long-period fiber grating (LPFG) with a permanent magnet to measure electrical current in unmanned aerial vehicles (UAVs) The proposed device uses a neodymium magnet attached to the grating structure, which suffers from an electromagnetic force produced when the current flows in the wire of the UAV engine Therefore, it causes deformation on the sensor and thus, different shifts occur in the resonant bands of the transmission spectrum of the LPFG Finally, the results show that it is possible to monitor electrical current throughout the entire operating range of the UAV engine from 0 A to 10 A in an effective and practical way with good linearity, reliability and response time, which are desirable characteristics in electrical current sensing

Design and development of DC high current sensor using Hall-Effect method

Abstract: This paper report a newly developed high DC current sensor by using a Hall effect method and also the measurement system. The Hall effect sensor receive the magnetic field generated by a current carrying conductor wire. The SS49E (Honeywell) magnetoresistive sensor was employed to sense the magnetic field from the field concentrator. The voltage received from SS49E then converted into digital by using analog to digital converter (ADC-10 bit). The digital data then processed in the microcontroller to be displayed as the value of the electric current in the LCD display. In addition the measurement was interfaced into Personal Computer (PC) using the communication protocols of RS232 which was finally displayed in real-time graphical form on the PC display. The performance test on the range ± 40 Ampere showed that the maximum relative error is 5.26%. It is concluded that the sensors and the measurement system worked properly according to the design with acceptable accuracy.

Apparatus and method for an electric power supply

Abstract: A battery-sourced electric power supply for use in electric drives, having at least three battery modules 5101-5112, each connected to at least one other battery module. Switches allow the electric connectivity between batteries to be changed. A battery subportion portion may be electrically connected in series or in parallel with a second battery subportion, or a battery portion can be bypassed. In a preferred embodiment the battery circuit is connected to an electric machine 5113, an auxiliary power bus 5114, a charging terminal 5115, and an electronic controller 5116. The device integrates the traction battery and power convertor into a single unit, removing the need for an inverter. The electrical circuit may also have a charge equilibration or charge equalization module, which itself may comprise a voltage sensor, and/or a current sensor. The electrical circuit each have one or more of the following: a voltage sensor, a temperature sensor, an acceleration sensor, a current sensor. Also claimed is a method for generating an electrical voltage for an electrical load by reconfiguring the connectivity of at least two battery subportions by switching connectivity states, allowing for voltage to be changed over time and containing sinusoidal segments similar to three-phase AC.

A modular, extendible and field-tolerant multichannel vector magnetometer based on current sensor SQUIDs

Abstract: We present the prototype module of our extendible and robust multichannel SQUID magnetometer system. A large multi-module arrangement can be implemented by using up to 7 modules. The system is intended for high-precision measurements of biomagnetism and spin precession. Further demanding applications are magnetorelaxometry and ultra-low-field nuclear magnetic resonance (ULF NMR), where pulsed magnetic fields of up to 100 mT are typically applied. The system is operated inside the Berlin magnetically shielded room (BMSR-2) and equipped with 18 magnetometers consisting of niobium (Nb) wire-wound pick-up coils. A total of 16 small pick-up coils with 17.1 mm diameter form a regular grid with individual channels arranged to ensure system sensitivity covers all three orthogonal spatial directions. Two large hexagonal pick-up coils with an equivalent diameter of 74.5 mm sensitive in z-direction surround the grid at two different heights and are suitable for the detection of deep sources. Each pick-up coil is connected to the input of a thin-film Nb SQUID current sensor via a detachable superconducting contact. The SQUIDs are equipped with integrated input current limiters. Feedback into the pick-up coils is employed to minimise crosstalk between channels. The current sensor chip package includes a superconducting shield of Nb. The field distortion of the prototype and a multi-module arrangement was analysed by numerical simulation. The measured noise of the small magnetometers was between 0.6 and 1.5 fT , and well below 1 fT for the large ones. Using a software gradiometer, we achieved a minimum noise level of 0.54 fT . We performed ULF NMR experiments, verifying the system's robustness against pulsed fields, and magnetoencephalographgy (MEG) on somatosensory evoked neuronal activity. The low noise performance of our 18-channel prototype enabled the detection of high-frequency components at around 1 kHz by MEG.