Excitation Circuit With Negative Feedback for a Borehole 4He Optically Pumped Sensor Based on an ELM-Hammerstein Model

Stability in the emission intensity of a spectral lamp is an essential factor determining the performance of a4He optically pumped sensor (He-OPS). However, in an He-OPS, the stability of the lamp drive signal source is greatly affected by temperature. This is a huge obstacle to its application in borehole magnetic surveys, which have harsh conditions such as a confined environment and high temperatures. Hence, a real-time control excitation circuit with proportional integral derivative (PID) feedback regulation to enhance the stability of the emission intensity is proposed in this article. The instability of the luminous intensity was first analyzed theoretically and an extreme learning machine (ELM)-Hammerstein model was established. Then, instability was regulated in real-time using a programmable PID controller. Experimental results indicate that the designed excitation circuit can work at environment temperatures up to 75 °C and magnetic drift of up to 1.3 nT is suppressed. Therefore, the excitation circuit with PID feedback regulation is an effective and reliable way to improve measurement stability and has potential for utilization in extreme environment applications such as borehole magnetic field measurement to detect resources and monitor seismic activity.