Certain aspects of the present disclosure provide methods and apparatus for closed-loop control of a system using one or more electron paramagnetic resonance (EPR) sensors located on-site. With such EPR sensors, a change can be applied to the system, the EPR sensors can measure the effect(s) of the change, and then adjustments can be made in real-time. This feedback process may be repeated continuously to control the system.

An electromagnetic (EM) receiver system for measuring EM signals. The EM receiver system includes a survey EM transmitter for generating survey EM signals within a first frequency range; a tracking EM transmitter for generating tracking signals within a second frequency range; and a receiver section including a receiver that measures both the survey EM signals and the tracking signals.

The present invention relates to the field of coal mine concealed fire zone detection, in particular to a coal spontaneous combustion downhole detection system and method based on a self-potential method. The coal spontaneous combustion downhole detection system comprises a self-potential detection apparatus and a self-potential processing apparatus; the self-potential detection apparatus comprises measuring electrodes, a reference electrode and metal anchor rods; the measuring electrodes are arranged on a top plate of a goaf roadway, are fixed to the metal anchor rods, and are in wireless connection with the reference electrode through the metal anchor rods; the self-potential processing apparatus comprises a data processing sensor for processing potential data and an imaging sensor for converting data into images; and the measuring electrodes and the reference electrode are in wireless connection with the data processing sensor.