Abstract
Abstract. Current data are an important input data for electrical prospecting data postprocessing. The existing current recorder is inadequate for continuous recording, precision, bandwidth, dynamic range, and input range. A new full waveform current recorder that is ideal for measuring current signal for electrical prospecting applications is presented. The new measurement principle enables the fabrication of a high-precision current sensor with an autonomous data logger as well as continuous measurement capabilities for full waveforms that are comparable to recent developments for electrical prospecting applications. The full waveform current recorder is capable of measuring current with bandwidth from direct current (DC) to 10 kHz, with a power spectrum density noise floor of 10 µA/rt(Hz) at 10 Hz. The current recorder has a dynamic range that is higher than 97 dB over a range of 100 A at peak, with time synchronisation error as low as ±0.1 µs. These features make new current recorder a promising technology for high-precision measurement with long-duration, autonomous data logging for field electrical prospecting applications.
Highlights
Electrical prospecting contains many branch methods, such as time-domain-induced polarisation (TDIP) (Fiandaca et al, 2012), spectral-induced polarisation (SIP) (Vanhala, 2010), direct-current resistivity (DCR) (Monteiro Santos and Elkaliouby, 2011), magnetotellurics (MT) (Cagniard, 1953), and controlled source electromagnetic surveying (CSEM) (Boerner et al, 1993a), which have been successfully applied on mineral exploration, hydrocarbons prospecting, and groundwater investigation
For the application of the controlled source audio magnetotelluric (CSAMT) method (Boerner et al, 1993b; Di et al, 2017), the current is not used as the input for data postprocessing, but the current data can provide a reference for the evaluation of the transmitter quality
The current recorder is connected close to the transmitter without any injection, and an internal GPS that accurately provides a pulse per second (PPS) signal allows the device to store a continuous series with high-precision time stamping, which is crucial for correlating and processing data from an EM receiver installed nearby
Summary
Electrical prospecting contains many branch methods, such as time-domain-induced polarisation (TDIP) (Fiandaca et al, 2012), spectral-induced polarisation (SIP) (Vanhala, 2010), direct-current resistivity (DCR) (Monteiro Santos and Elkaliouby, 2011), magnetotellurics (MT) (Cagniard, 1953), and controlled source electromagnetic surveying (CSEM) (Boerner et al, 1993a), which have been successfully applied on mineral exploration, hydrocarbons prospecting, and groundwater investigation. To meet the requirements for current measurement in high-power multifunction transmitters, which use PRS waveform and broad bandwidth CSEM, certain deficiencies in the input range, precision, bandwidth, and continuous recording should be addressed. Considering the above analysis, an acceptable current recorder should have the following characteristics: (1) a suitable input range for a high-power multifunction transmitter; (2) acceptable precision for amplitude measurement; (3) accurate and consistent time synchronisation while recording the current to decrease phase calculation error; (4) continuous current sampling and full waveform recording for current amplitude and phase variable. The development of current recorders mainly focuses on the accuracy of the amplitude, the accuracy of time synchronisation, broad bandwidth, and continuous recording at a large input range for full waveform recording
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