from Terraplus

The KT-20 offers a complete handheld solution for mineral exploration, geological sampling, core logs or soil science. The instruments ability to record Magnetic Susceptibility, Conductivity/ Resistivity, Density, Induced Polarisation and Geospatial Position enables the Exploration Geophysicists to map and characterise samples effortlessly. The KT-20 supports a number of different sensors in order for the instrument to be optimised for a particular application. Both the coil shape and frequency can be varied by changing the sensor.

KT20 with circular dual frequency coil. Image courtesy of Terraplus.

Each instrument is supplied with a pre-installed calibration curve. The conductivity calibration is based off a multi-point algorithm to ensure accurate measurements between inductive and galvanic methods. The magnetic susceptibility calibration curve is derrived from samples with containing various concentrations of magnetite, enabling the KT20 to calculate an estimated direct iron ore concentration (%). Alternatively operators are able to formulate and save their own calibration curves.

The KT-20’s unique design enables users to interchange between the circular, rectangular or large 3F-32 field coil on the fly. The circular sensor has a large surface area and is recommended for grassroots exploration and measuring samples larger than 66 mm. Conversely, the rectangular sensor is ideal for measuring cores with diameters smaller than 66 mm.

The KT-20 S/C is available with two dual-frequency sensors: 1/10 kHz or 10/100 kHz. Those focusing on magnetic susceptibility measurements will benefit from the 1/10 kHz sensor because the 10 kHz frequency provides a higher sensitivity, whilst the 1 kHz frequency reduces the influence of a sample’s conductive properties on the measurements, in addition to providing a greater depth penetration (although with a reduced sensitivity). The 10/100 kHz is advantageous for conductivity measurements because the 100 kHz frequency increases the meter’s sensitivity to 0.1 S/m, while the 10 kHz has a greater depth penetration (although with reduced sensitivity).

Coil Types

  • 1/10 kHz Dual-Frequency Sensor (circular or rectangular designs)
  • 10/100 kHz Dual-Frequency Sensor (circular or rectangular designs)
  • 10 kHz Single-Frequency Circular Sensor (circular design only)
  • 10 kHz Single-Frequency Curved Sensor for Magnetic Susceptibility Measurements (available only in dedicated BQ, NQ, HQ and PQ diameters)

The 3F‐32 sensor has a 32 cm diameter and features three frequencies that have been carefully selected to provide certain benefits for magnetic susceptibility and conductivity measurements. The 3F‐32 sensor is equipped with a telescopic pole and arm support enabling users to easily and comfortably take measurements while standing or walking. The KT‐20 with 3F‐32 sensor is an ideal instrument for field research. It can take a single measurement at a specific location, or continuously collect data to map an entire area. A GPS receiver is integrated into the KT‐20 console to provide location coordinates with the data. It also has a built‐in high resolution digital camera to visually document any sample of interest.

Induced Polarisation measurements require the samples to be placed sample holder similar to a vice. The device is portable so samples can be processed and measured at base camp. The IP/Resistivity sensor can be supplied as a Standard and Pro model.

The Standard model calculates total chargeability (M_x) using two methods: 20 windows and Mx fit. The first measures total chargeability using the traditional 20 windows method. The second, Mx Fit, is an algorithm that measures total chargeability using several thousand windows instead of 20. The benefit of Mx fit is that it provides increased accuracy and confidence in the measurements.

The Pro model enables the user to analyse decay curves with up to 16,000 data points for any measurement time. Through these data points the decay curve is studied to calculate total chargeability (M_x) and initial chargeability (M_ip). Users can also customise their own chargeability windows (M_x_user) and time periods (t1 and t2). Furthermore, an extra early delay time (as fast as 2 ms after turn-off) allows the Pro model to collect data much earlier than before, providing users with new capabilities to improve their interpretation. The KT-20 IP Pro model includes all of the same capabilities as the Standard model.

Application Notes

Precision agriculture

The intensive nature of agricultural farming can result in a large amount of spatio-temporal variation in soil. Magnetic susceptibility can be used to detect iron-containing minerals which are found in soil, sediment and rocks. An elevated presence of heavy metals (eg from high traffic volumes) can be detected using magnetic susceptibility measurements. These heavy metals on agricultural land can affect food quality and safety; hence this method is becoming important for monitoring environmental pollution. The magnetic properties of soils have also been linked to the organic matter content, making this of particular interest to precision agriculture farmers.

The conductivity component can provide information about soil properties that affect crop productivity. These include organic matter level, salinity and drainage conditions. The porosity and hence also the density are influential factors too, as this will determine the volume of water that can be held in the pores. And finally the measured conductivity may be affected by colloids, specifically those associated with organic matter.

Mineral exploration

The KT-20 has the ability to accurately measure magnetic susceptibility, which is used extensively to determine the magnetic properties of rocks. This is vital for mineral exploration as magnetic susceptibility is related to the concentration and composition of magnetisable material contained in a sample. Magnetisable material includes magnetite, hematite, iron, titanium oxides and clay minerals (chlorite, smectite and glauconite). It can also display an estimated iron ore concentration (%) through the pre installed calibration curve.

The conductivity aspect of the KT-20 is particularly useful in mineral exploration because the target ore minerals generally have a high conductivity compared to the rock types with which they are associated. Metallic ore minerals can significantly affect the bulk resistivity/conductivity of a sample, even in small quantities.

The induced polarisation measurement with the KT-20 gives a dimensionless quantity known as chargeability. These measurements are influenced by minerals which conduct by electron flow, including pyrite and graphite. Clay minerals may also affect the IP measurements however this would be of a smaller magnitude.


Magnetic susceptibility in archaeology can be used to locate traces of previous human habitation, for example building foundations, field systems and areas of burning. The remains of a fire can affect magnetic susceptibility because silt particles and iron oxides can be transformed into very magnetic oxides through burning, and when the organic matter in soil burns it can change hematite to magnetite. Thus increased magnetic susceptibility hotspots could be due to large fires, hearths and kilns. If spikes are present in vertical sections of magnetic susceptibility data, this would indicate a burned layer. Magnetic susceptibility surveys are often used as a precursor to more in depth magnetic surveys. It is an effective way to determine areas of potential archaeological activity. The IP resistivity of samples can provide information on the presence of disturbed clay in an area which has previously been occupied by humans.


Magnetic susceptibility measurements can efficiently be used on soil and sediment samples to monitor anthropogenic pollution. These measurements can be used to identify polluted areas, and then to map these areas. Since the magnetic susceptibility is sensitive to ferromagnetic elements such as nickel, lead and zinc the KT-20 can be used to monitor pollution around industrial sites – both past and present. Heavy metal elements (iron, copper, manganese and nickel) have been shown to produce a correlation with magnetic susceptibility, indicating it is possible to use these as proxies for contamination.


Can I use the KT-10/KT-20 to measure small chips, pebbles, shavings, or powder samples (for example, drill chips from reverse circulation drilling)?

Yes. With some preparation, both the KT-10 and KT-20 can be used to measure the magnetic susceptibility and/or conductivity of small chips, pebbles, shavings, or powder samples. In order to make an accurate measurement, the samples should be formed into a bulk sample that is larger than the KT-10/KT-20’s sensor (i.e. larger than the 66 mm diameter for circular sensors) with a thickness of at least 5cm (~2 inches). The samples can be aggregated in a thin plastic bag or glass container (e.g. Petri dish).

What are calibration and reference pads? Do I need one for my KT-10/KT-20?

Calibration/reference pads are used as a check source to verify the accuracy of measurements taken by the KT-10 and KT-20 systems, whether for magnetic susceptibility, conductivity, or IP/resistivity. Calibration pads have the added benefit of allowing users to recalibrate their magnetic susceptibility measurements. Although they’re not required, these pads can prove to be useful tools in validating your measurements. Many groups have a policy of testing their KT-10/KT-20 units at the beginning and end of each work day. These pads are particularly useful when multiple KT units are being used on a project to confirm that each of them is measuring a similar value.

A variety of different calibration/reference pads are available depending on the method being measured. Each pad comes with a test certificate and is compatible with a range of different models. All of the pads are compatible with the KT-20 system, subject to the type of sensor being utilized, and all Flat magnetic susceptibility and conductivity pads are compatible with the KT-10 system. Although the pads are designed for the KT-10 and KT-20 systems, they can also be used with other instruments. Magnetic Susceptibility Calibration Pads

Magnetic Susceptibility Calibration Pads

Magnetic Susceptibility Calibration Pads

Conductivity Reference Pads

KT 10 & KT 20 Conductivity reference pads

IP/Resistivity Reference Pad

A dedicated reference pad, the IP-T10, is also available to verify the various measurement parameters shown below of the KT-20’s IP/Resistivity Module.

IP/Resistivity Reference Pad

Note Measurement values are influenced by external factors, such as temperature, environment, and the operator’s technique during the measurement sequence (e.g. the pressure applied on the sample during measurement). This may lead to slight differences observed between the measurement and the nominal value indicated for each pad.

What is the conductivity sensitivity for the various KT-10 models and KT-20 sensors?

Refer to the charts below for the range of conductivity sensitivities available.

KT 10 Cond Sensitivity

The conductivity sensitivity for the KT-20 system is dependent on the sensors being used with the KT-20 console. See below for a breakdown of the conductivity sensitivities available with each applicable KT-20 sensor:

KT 20 Cond Sensitivity
What is the depth penetration for the KT-10 and KT-20 system?

The depth penetration for the KT-10 and the KT-20’s standard sensors is approximately 4cm, with 90% of the readings coming from the first 2cm of a sample. The KT-20 can achieve greater depths when combined with the 3F-32 large diameter sensor. The 3-frequency (1/10/100 kHz), 32cm diameter (3F-32) sensor has a depth penetration of +/– 32cm (subject to the electrical properties of the soil, the frequency used, and the size and characteristics of the source being measured) and is recommended for agriculture, archaeology, and environmental investigations.

What is the magnetic susceptibility sensitivity for the various KT-10 models and KT-20 sensors?

Refer to the charts below for the range of magnetic susceptibility sensitivities available.

KT 10 Sensitivity chart

The magnetic susceptibility sensitivity for the KT-20 system is dependent on the sensors being used with the KT-20 console. See below for a breakdown of the magnetic susceptibility sensitivities available with each applicable KT-20 sensor:

KT 20 Sensitivity
What sensors are compatible with the KT-20 system?

There are a variety of sensors compatible with the modular KT-20 system. For measuring magnetic susceptibility and/or conductivity, the following sensors are available:

KT 20 sensor options

Other options include an IP/resistivity sensor for measuring chargeability and resistivity (available with either a small or large sample holder to facilitate measurements for various sample sizes) and a density scale assembly for measuring the density of a sample through water displacement.

What upgrades are available with the KT-10 and KT-20 system and how do they work?

All “Remote” upgrades are available upon purchase or can be added remotely via an online firmware upgrade, eliminating the need to send the unit back to Terraplus. Remote upgrades are accessed by entering an unlock code (provided by Terraplus) on the GeoView software or, in the case of the KT-20, on the device itself. Any upgrade added after the initial purchase is subject to an upgrade fee.

Note that all KT-20 upgrades apply to the console itself, rather than the individual sensors. For example, once a KT-20 console has been upgraded with the Plus functionality, all applicable sensors connected to the console will have access to the upgrade – including sensors purchased at a subsequent date.

KT 10 & KT 10 Upgrades