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AgTEM towed TEM electronics

AgTEM towed TEM electronics is only available at the discretion of our electronics provider and is specifically designed for Wallaby and Wallaroo. In contrast with TerraTEM and TerraTEM24, AgTEM towed TEM electronics is designed for continuous acquisition in walked use, including in-loop to some extent, and vehicle dashboard use, can efficiently regulate output voltages from 3.5 to 18V for efficient small loop operation, and allows for many loop connection options. Conventional TerraTEM and TerraTEM24 do not come standard with the continuous acquisition option but addition can be negotiated with Monex as can the efficient voltage regulation. AgTEM electronics is split into a transmitter, with or without small internal batteries that can operate the whole system for about one hour, a receiver, a dashmount or pivot mount touchscreen/computer, and optional large external batteries used for extended high power operation. In standard configuration, the transmitter and receiver are connected by a synchronization cable and power cable and the GNSS receiver can be one within the computer, or can be one with full view of the sky, on top of a vehicle cabin. In contrast, The TerraTEM and TerraTEM24 have all components, except batteries, within one box and must be positioned on a vehicle seat adjacent to the driver for operation and are not suited to continuosuly walked operation. AgTEM-electronics are designed to be backpackable with strain and rain protected connectors and ability to continue operating in rain. Flexible loop connectors facilitate rapid whole of system testing using shorted loop turns and loop interchanges.

Electronics and firmware in this product is made by our electronics provider but packaging is conducted by Groundwater Imaging Pty Ltd to tailor to towed TEM requirements. Warranty and service are provided by Groundwater Imaging Pty Ltd

AgTEM-electronics operate at 200Hz, 100Hz or 25Hz, or lower, full waveform frequency, which is equivalent to stacking frequencies of 400Hz, 200Hz or 50Hz as quoted by a competitor. These frequencies are for countries with 50Hz power. For 60hz power countries the frequencies are 240Hz, 120Hz and 30Hz, or lower. Realize that high frequency is good for reducing noise but low frequency is essential for imaging deeply in all but resistive terrain, and for some forms of movement noise removal.

AgTEM electronics continuously update display of data as coloured posted point maps and as decay curves with an all-important reference curve for gradual fine comparison of change during survey.

AgTEM receiver A/D conterters are 24bit Sigma/Delta type for low noise operation and are coupled with overload protection and signal amplification of 1x, 10x or 100x. The system is protected for operation under power lines. Pre-amplifiers positioned on receiver loops further add amplification, low-pass filtering, damping and reduction of systemic noise pickup in connection leads.

AgTEM-electronics operate from <1Amp (for test loops such as shown below) up to 45 Amps (practically about 40Amps). Ramp time is kept manageable using 200 Volt avalanch voltage to give ramps typically on Wallaby of 6 to 9 uS into single turn 6 x 6m loops. Higher avalanch voltage would add to late time waveform decay, electrocution danger, cost and weight while lower avalanch voltage would increase ramp times.

AgTEM-receiver is fully sealed with a pressure equalization vent and cross-case heat conduction coupled with internal fan-forced circulation. High quality A/D conversion and preamplification requires considerable power so the entire case is made of heat conducting aluminium such that operation in excess of 40 degrees celcius ambient temperature is feasible. This case can only be used rigidly fixed withon the transmitter loop but is fine at more than 1m outside of it. The receiver must not be fully packed into an additional box that prevents escape of heat if used in hot conditions.

AgTEM-transmitter is air cooled via an elaborate system designed to keep metal content, problematic when in or near transmitter loops, to a minimum. In an internal chamber, air circulation is fan forced and heat generating components and heat absorbers are fixed to heat sinks that sink heat through a 'firewall' to a fan-forced ventilated tunnel connected through the battery compartment which is open to the atmosphere via the rain protected cable entry port and another rain protected vent. 

AgTEM input power can be supplied either by: 

- 2 x 7AmpHr 12.8V LiFePO4 batteries commonly used in security systems, 20 of which can be carried in hand luggage on commercial aircraft,

- 25.8V (nominally 24V) 54AmpHr to 120AmpHr LiFePO4 batteries suitable for continuous operation for a full 12 hour day (at up to full power with the 120AmpHr option), or

- 2 x any 12V (or 12.8V) batteries of opportunity as can be sourced at remote localities.

 For further interim details please see the AgTEM, Wallaby and Wallaroo pages or contact us because many details and features not listed are under development and/or subject to negotiation. For instance, features of dual transmitter operation and multiplexed dual transmitter loop outputs and continuous current adjustement are pending completion as of November 2024. In the photos below, see all the hardware is capable of these options but firmware still is not ready. Linear time gate storage, for improved noise post processing, and operation at up to 625 kHz sampling frequency (in just one or two receiver channels simultaneously due to data storage limitations) have been partially tested and can be negotiated for commercial release. Similarly, negotiation can occur on facilitated testing of GNSS time pulse synchronization for continuous survey with fully disconnected receiver and transmitter including Monex transmitters of up to 200Amps. In this form large fixed hand laid loops may be used with roving backpacked AgTEM-receivers and walked loops such as the large but very light collapsable Wallaroo Z-component receiver loops in front of the operator balanced across operator shoulders by a pair of smaller orthogonal X and Y component loops behind the operator. Such GNSS synchronization has been available and tested on the Monex products for many years. Airborne use of AgTEM electronics is restricted by 3rd parties.

Links & Documents

  • AgTEM
    • Airborne EM Compared With Land Based And Waterborne Systems