Frequently Asked Questions

About RM Frobisher

Our contact details are here.

Yes. RM Frobisher (1986) Ltd. accept payment by Credit or Debit Cards on our website. (We use 'Stripe' to process your payment.)

RM Frobisher (1986) Ltd use ‘’ to process debit and credit card payments. We also accept ‘BACS’ and ‘CHAPS’ bank transfer payments in UK pounds, USD United States Dollars and Euros. Please contact us for prices in other currencies.

If you would like to see our products you could visit us at our offices in Barnsley, South Yorkshire. (Please make an appointment or check that we are available before visiting.) We have an area close by where you can use a unit. RM Frobisher visit shows and have stands at archaeology conferences where we have samples you can handle see Meet Us for more information about where we will be this year.

Yes. We sell all our products and components individually. Check our website or contact us for a price list.

Yes. The TAR-3 uses standard 4mm gold plated jack plugs and can be used with any manufactures frame and probes. We would be happy to advise or produce adaptor leads to suit your current frame and probes.

We recognise the value of having agents and/or resellers. Please contact us if you would like to become an agent or reseller.

Yes. Our products meet the essential requirements of many countries and we are willing to ship (at your cost) to any destination. If we have a reseller or agent in your country, we may direct you to them as they would be better placed to offer support.

Yes, we would welcome resellers. Please contact us so that we can come to an arrangement regarding supporting our products and supporting you in your efforts.

Yes, but the unit must be shipped to you! If you are buying on behalf of a friend please let us have their details so we can register the unit to them. This will enable us to let them know about updates and allow us to carry out any repairs under warranty.

No, but we do offer a ten percent rebate to customers (companies or individuals) who purchase more than one unit at the current list price. The rebate reflects the savings we make by selling to one person or company. The rebate is available on purchases of multiple units and on the purchase of more units at a later date. (This does not apply to accessory kits)

Our products contain one of the latest 32bit ARM Cortex based processors, capable of running at speeds of up to 48MHz. The processor features built in Digital Signal Processing functions (DSP) allowing it to perform complex Fast Fourier Transform (FFT), Infinite Impulse Response (IIR), and Finite Impulse Response (FIR) calculations in a single instruction. This enables unwanted 50/60Hz mains “hum” to be removed using modern Digital Signal Processing techniques, giving it unrivalled power and performance.

We at RM Frobisher consider ourselves to be experts at interfacing equipment together. Please contact us with your requirements. This is an area that we wish to develop and are actively seeking partners.

Yes. We can produce one-off, customised, equipment. Producing customised equipment helps us at RM Frobisher increase our knowledge and understanding. A word of caution: One offs or the first off can be expensive as the cost of development is not spread over tens or hundreds of units. Please contact us with your problem or ideas, we may be able to help or suggest ways of solving your problem.

We at RM Frobisher are committed to ensuring that all our products are backward compatible with previous versions.  Our goal is to use the same mountings, plugs, sockets, cables (and pin outs), power supplies, and SD Cards (including data formats) in all of our products (all of the external features of our products).

The internal software, DSP techniques, and hardware design may evolve, be updated, or improved as new components become available (or as components become obsolete and are updated).

Note RM Frobisher may modify, change, redesign, alter or withdraw from sale its products at anytime.

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DFG-1 Magnetic Gradiometer

No! There are only a few settings and it takes less than 60 seconds to zero. The sensor does not need to be aligned. Once you have entered your settings they are remembered by the DFG-1 unit and reloaded ready for use when you switch the DFG-1 on.

The DFG-1 and Sensys FGM series sensors do not have a warm up time. Modern electronic techniques and components have eliminated the need to allow the equipment to warm up. We do recommend that you avoid subjecting the equipment to sudden thermal shocks just before use. (Such as moving the unit from a heated room to a cold outdoor environment or from an air conditioned environment to a hot one.) If there is a difference between the storage temperature and the operating environment you should allow the temperature of the unit to stabilise before using it. Fifteen minutes is sufficient.

The DFG-1 Magnetic Gradiometer's battery lasts for twelve hours after charging.

We keep the DFG-1 in and associated equipment in stock! There are three types of sensor. Sensors are usually available in five working days. Please contact us for details of sensor lead times.

The sensor does not need aligning! The design of the sensor eliminates the need to align it.

The output is compatible with

DW Consulting's TerraSurveyor and Snuffler

Data can be imported directly from the SD card. If required the data can be exported from Snuffler in different formats enabling it to be used with other software.

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TAR-3 Resistance Meter

No! There are only two setting the user may have to change:

1. The grid size in metres
2. The number of readings per metre

In many cases the default settings may not have to be changed! The advanced electronics and Digital Signal Processing (DSP) techniques automatically adjust the unit to obtain optimum performance.

The TAR-3 is Resistance Meter. It measures the resistance between the P1 and P2 probes and using the value of the injected current and records the measured (apparent) resistance. If the user has recorded the probe separation and offsets the TAR-3 results can be converted to resistivity.

The 'Factory Default' setting is 4mA. If the P1 and P2 probe resistance is very high, or the resistivity of ground being measured is high, the TAR-3 unit will reduce the current in stages to 2mA, 1mA or 0.5mA before reporting an error. Conversely, if the resistance being measured is very low the injected current is increased, up to a maximum of 8mA. This is one of the features of the TAR-3 that make it simple to use.

The TAR-3 has been designed with the user experience in mind.

The TAR-3's light weight minimises user fatigue, enabling operators to use the unit for extended periods. The shape of the TAR's handle allows users to change their grip and the rounded shape has no "Hard" corners to injure the operator's hands. The TAR-3 has a 32mm diameter grip to reduce the pressure on the operator's hands. The TAR-3's slim probes (8mm) reduce the force needed to insert them into the ground minimising operator fatigue.

For users who are not of average height, the frame of the TAR-3 is available in custom lengths. Please contact us with your requirements.

The TAR-3 is uses a lightweight Aluminium Alloy for its frame and high power lightweight Lithium Iron batteries, making it the lightest Resistance Meter in its class.

You can't measure the input impedance of the P1P2 voltage measuring circuit directly, as the full impedance is only developed when the circuit is powered up and actively measuring. The P1P2 probes are shorted together periodically (many times per second) to reduce the polarisation of the probes.

Voltages in excess of 60V will damage the TAR-3! If your TAR-3 comes into contact with voltages greater than 60V report yourself to the relevant health and safety body! If your TAR-3 is damaged by voltages greater than 60V consider yourself lucky - you could have been damaged or killed!

Nothing bad will happen! You can short any combination of probes together without causing any damage. The voltage probes P1 and P2 can measure voltages higher than the maximum produced by C1 and C2. Shorting C1 to C2 results in the voltage dropping so that the current flowing is the set current.

Yes. The TAR-3 unit uses standard 4mm gold plated jack plugs and sockets and can be used with any controller. Please let us know what unit you have and what connector and adaptors you require. We would be happy to advise or produce adaptor leads to suit your existing equipment.

The TAR-3 does not have an operating frequency. The internal electronics of the TAR-3 are digital and use the Digital Signal Processing (DSP) features of the embedded processor. To prevent electro chemical polarisation of the probes the polarity or the probes is switched between readings but 50Hz and 60Hz signals are digitally filtered from the result using advanced digital signal software techniques.

The maximum current injection voltage is limited by safety regulations. The voltages of the TAR-3 are classed as Safety Extra Low Voltage (SELV) which limits them to a maximum of 42.4Vac or 60Vdc.

WARNING Voltages above 42.4Vac or 60Vdc are no longer legal if they can be touched by a finger.

The input impedance of the Voltage measuring probes P1P2 is very high, in the order of 100,000,000,000 Ohm, 100,000 Mega Ohm, or 0.1 Tera Ohm. (That's 10 to the power 11 Ohm). The TAR-3 uses electrometer grade components and design techniques for its input circuits which have been tested with very high impedance voltage sources to confirm the input impedance.

Gold! 4mm jack plugs and sockets have more gold contact surface area than waterproof connectors. The standard (and military spec) connectors have a limited open/close, connect/disconnect, life span. Gold plated 4mm jack plugs have a longer life as they have a much greater surface area and the plugs orientation changes with each insertion which extends their life further.

The TAR-3 uses a 32bit processor and 18.5 bit Analogue to Digital Converters (ADC) with a range of 262,144 (as opposed to 2047 for 12bit systems) . Using precision electronics in the analogue circuits it is possible for resistance measurements to have a standard deviation of 0.12% of the reading (better than one in eight hundred). The current between C1 and C2 and the voltage across P1 and P2 are determined using the full 18bit (plus sign bit) range of the ADC and are processed using modern digital signal processing techniques (DSP) using the processor's built in DSP functions and hardware to produce a reading that is unaffected by 50Hz (and 60Hz) mains "Hum".

To put the accuracy in to perspective. 0.12% of a ton of water (1000kg) is 1.2kg which is about two pints.

The output is compatible with

DW Consulting's TerraSurveyor and Snuffler

Data can be imported directly from the SD card. If required the data can be exported from Snuffler in different formats enabling it to be used with other software.

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Selecting 'Line Mode' disables the normal 'Grid Mode' and configures TAR-3 Resistance Meter for measuring pseudosections in Line Mode - see Line Mode Section Kit for details

No! You can make your own probes and cables.

The probes must be made from stainless steel, other metals may produce Galvanic Voltages that are too large for the TAR-3 system. You will also need two long leads with at least one 4mm connector per lead. You can buy crocodile clips online and at many electrical suppliers.


No! You can use four probes, but you will have to insert them multiple times at the same spot which may cause problems with some readings. On a damp overcast day this is not problem. On a dry day pushing the probes deep into the ground to reach moist (conductive) soil can be tiring.

The TAR-3 Resistance Meter measures the Apparent Resistance (R) in Ohm (Ω). You can convert the measured resistance into resistivity (ρ, in Ωm) using the Wenner equation:


where a is the probe separation in metres (m). This version of the equation is for when the depth of the probes is small compared to the probe separation (a)

The 'DAT' output file saves the results in resistivity (Ω.m).

No! This is a manual system. You must move the crocodile clips (or probes) between each reading. This takes time and effort but it is a low cost solution!

Electrical resistivity tomography  (ERT)

The results file saved to SD Card is compatible with Geotomo Software’s RES2DINV.

The TAR-3 can be used with the Wenner array probe configuration

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MULTI-5 Option FAQ

The TAR-3's MULTI-5 option is a factory fitted PCB, Ten Way MILL specification socket and software upgrade to the standard TAR-3 unit and a separate enclosure with inputs for the TAR-3' injection current (Red socket) and voltage measurement input (Blue socket) It has file Input/output sockets (D,E,F,G, and H) that can be programmed to form a sequence of readings such as (DE), (DH), (HD), (GH) .... There can be up to 14 steps in a probe sequence.

A Probe Sequence contains the steps (measurements) the TAR-3 unit takes for each reading in the grid.

The sequence (DG),(DE),(ED) connects the 'C' socket to the &aposD' probe and the 'P' socket to the 'D' probe. When both probes make contact with the ground and current flows from probe 'D' to the remote 'C' probe the TAR-3 records the voltage between the remote 'P' probe and the 'G' probe. The TAR-3 unit then switches to the 'DE' probes and takes a second reading.

Note The third probe combination 'ED' swaps the 'CP' compared to 'DE'

The  'Probe Sequence' is stored in a text file on the TAR-3's SD card. It can be edited using a text editor such as MicroSoft's Notepad™. The probe sequence can also be created (and edited) using the TAR-3 unit.

The current EAC GUIDELINES FOR THE USE OF GEOPHYSICS IN ARCHAEOLOGY recommend that the remote probes are at least 30*'Probe spacing' distant from the traveling probes.

We suggest that the remote probes a place at the following distance from the edge of the grid

Be consistent, it is better to site the probes further away than too close.

Recommended Remote Probe Distance for each Probe Spacing
Cross Bar Distance (m)
Standard Cross Bar (0.5m) 15m
Extension Bar (1.0m) 30m
Array Bar (1.5m) 45m

In Wenner's 1916 work he recommends that the two sets of probes should have the same spacing. This is not possible when using the MULT-5 unit

Be consistent, we suggest the following spacings.

Suggested Probe Spacing
Cross Bar Spacing(m)
Standard Cross Bar (0.5m) 0.5m
Extension Bar (1.0m) 0.5m
Array Bar (1.5m) 0.5m

By using a 0.5m remote probe separation, all readings taken with the output of the MULTI-5 unit traveling probes set to 0.5m will meet the requirements of the current EU (UK) guidelines and be consistent with the results obtained using the standard 0.5m cross bar. Traveling probe separations of 1.0m and 1.5m will not meet Wenner's requirements but will have the same offset error factors.

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The TAR-3 GNSS Mode is an extra, factory fitted, PCB enabling a TAR-3 unit to receive NEMA 0183 GNSS data sentences transmitted by your satellite positioning system via its RS232 serial communication port.

No! The TAR-3 unit does not contain a Global Positioning System Satellite (GNSS) receiver. The additional PCB is to connect the TAR-3 to a GNSS system.

The TAR-3 unit has a three way 'MIL' spec socket that mates with the plug on the supplied cable. The other end of the cable has bare wire ends (Ground and TAR-3 Signal IN [GNSS signal OUT]). We supply 9 way DSUB solder bucket connectors.

You will have to solder on a connector that mates with your GNSS unit to the cable supplied. (Two wires)

A TAR-3 GNSS Mode system can connect to any system that outputs NEMA 0183 Data sentences via RS232 cables/signals.

The TAR-3 GNSS unit can record any ASCII data string with a '$' starting character and terminating with a 'LF' character. If the data string contains a checksum character the TAR-3 calculates the  received strings checksum and compares it with the transmitted checksum.

The TAR-3 can read and store ten NEMA 0183 sentences per second (10Hz) which is the maximum NEMA sentence output rate. The maximum length of a NEMA 0183 data sentence is 82 characters.

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TAR-3 Wheel Mode FAQ

The TAR-3's Wheel Mode allows users to push the TAR-3 along continuously measuring the apparent resistance of the ground and log the results to the SD Card every 0.25m (four readings per metre).

The TAR-3 wheel mode consists of the latest TAR-3 software and additional hardware.

1. The TAR-3 Spiked wheels (two off) and,

2. An additional factory fitted PCB

No! The Wheel Mode PCB can only be fitted by RM Frobisher (1986) Ltd. If you already have a TAR-3 unit we can fit a Wheel Mode PCB to it.

No! Wheel Mode and GNSS Mode have and extra PCB fitted to the TAR-3 and we can only fit one PCB to a TAR-3 unit.

TAR-3 Wheel Mode unit are made to order. We hold stocks of TAR-3 units, Wheel Mode PCBs, and spiked wheels. It usually take ten working days to from the receipt of your order to assemble, test, and ship a wheel Mode unit.

You can walk at up to five miles per hour (8 kph, 2.25ms-1) and stop and start while taking readings.

No! The TAR-3 Wheel Mode Spiked Wheels can only be used with a RM Frobisher TAR-3 unit.

No! The Wheel Mode unit contains strong magnets!

We recommend that you do not place Magnetic Gradiometers close to the Spiked Wheels.

No! There are limitations to where you can use the TAR-3 Wheel Mode.

The ground should be moist, not too hard and relatively flat. If the ground is too hard or dry the spikes cannot make contact with conductive soil. If the soil is too hard or dry you may have to use the normal probes. In extreme conditions even the probes may not be able to make contact with the conducing soil.

Two. The TAR-3 wheeled unit has two spiked wheels. They replace the traveling probes when measuring the grounds resistance using the twin probe method.

The wheels are attached to a standard TAR-3 frame in place of the TAR-3's probes. The wheel spacing is 0.5m - the same as the probes.

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RM Pro Cart System FAQ

No, due to the high value of the RM Pro Cart System you cannot purchase it online. You can order a system and pay a ten percent deposit online and the balance before delivery.

If you use a credit card to pay a deposit towards the cost of a system and pay the rest with another payment method (BACS, cheque or cash)  your credit card provider will guarantee the whole amount of the purchase if: "The item you’re buying costs more than £100 and less than £30,000".  Your purchase is covered by "Section 75 of the Consumer Credit Act 1974"

Our credit card processor charges a percentage of the total amount. This can exceed £800 on the total system cost, which would have to be added to the original price. By charging a refundable ten percent deposit we can keep our costs (and prices) low and your money is protected by "Section 75 of the Consumer Credit Act 1974"

This is a UK law - overseas buyers should check with their credit card provider for a similar provision in their own country's laws.

Plywood, Delrin®, and Nylon!

The RM Pro Cart is made from non-magnetic materials and contains no metallic components. The cart does not contain any metal!

The Plywood is marine grade to BS 1088:2018 The machined parts are coated with a microporous coating to provide additional protection from the elements.

Delrin is manufactured by DuPont™ and is a high-performance acetal homopolymer (Polyoxymethylene POM) which is an ideal material for parts designed to replace metal as it combines low-friction and high-wear resistance with the high strength and stiffness.

Nylon was first produced by DuPont but is now produced by many companies. All the nuts and bolts used in the RM Pro Cart are manufactured using 'Nylon 66' because of its toughness.

Molybdenum disulfide (MoS2) filled Delrin is used for the bearings. It has a low coefficient of friction and good wear resistance which makes it an excellent choice for low speed, low load applications such as the RM Pro Cart

Plywood is a much maligned material. It is supplied in a wide range of qualities: from 'disposable' grades used in packing crates through to engineering, structural grades used by us. The marine grade used by RM Frobisher has known and consistent mechanical properties. it is strong and tough.

The cart can be packed flat; you can stand on the parts without damaging them. You can place them flat on the floor of your vehicle and stack other equipment on them. If you manage to break one of the plywood components it can be repaired or replaced onsite  - just visit your local 'DIY' store (you can use unbroken part as a template).

Should the need arise - spare parts are available from us.

We use custom brackets machined to a fine tolerance to fit the sensors. The sensors are then held in place by friction and an elastic 'bungee' cord. We buy a UV stabilised braided polypropylene sheathed cord in bulk rolls from a dedicated supplier but replacement cord is available on-line and at many local shops.

The fittings at the end of the cord are held in place with a knot - commercially produced fittings often use magnetic steel crimps!

Do not be tempted to use ready made cords as they may be magnetic!

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Battery Information

Yes, Li-Ion-Ion batteries do cost more than NiMH or NiCd batteries but they have less 'charge memory' and are more efficient than NiMH batteries when charging. 80 to 90 percent of the charging current is stored compared to approximately 60% for NiMH batteries. They charge much faster for a given input current which means less time waiting!

Our products have no special storage requirements. Like all electronics they should be stored in a dry location at temperatures between -20 Celsius and +30 Celsius: Long term storage above 30 Celsius is not recommended

We recommend that that units are stored with the back panel removed and the storage case slightly open. This is to enable the foam and case to dry – if the unit has been used in damp/humid conditions any moisture in the sealed case can condense on the pcb, which over months and years may cause corrosion.

Li-Ion batteries are charged in two stages “Constant Current” and then “Constant Voltage”. During the second stage the current flowing into the batteries drops as the batteries’ voltage rises to the that of the charger. As the voltage rises the charging current drops to zero. The final milli-Volt rise is takes a long time in comparison to the rest of the charging schedule. “Topping Up” or saturation charging is squeezing the last one percent (or less) of charge into the Li-Ion cells.

Users can switch the charger off and omit the “Topping Up” if they want to as it’s unlikely that they will need the last one percent (or less) of battery charge 99% of the time.

Li-Ion batteries are expensive, need a dedicated charging circuit and may have to be declared when shipping or travelling with them but their advantages far outweigh their disadvantages. Li-Ion batteries’ power to weight ratio makes them the best choice for modern equipment. The batteries in the TAR-3 last for up to twenty hours and only weigh 100g (less than four ounces) that’s about the same weight as ten and a half one pound coins or thirteen Euros. As the TAR-3 has to be picked up 400 times per twenty metre grid the saving in weight does matter. The built-in dedicated battery charger in RM Frobisher’s products uses any 5V USB power supply or socket

Yes, the voltage can drop slightly after charging. This is often referred to as “relaxing” or “settling”. The voltage drop can be around 0.1V. You will quickly develop a “Nose” for how long the batteries last for you. Don’t be too worried about battery life. They last a long time and can be charged up enough in 30 minutes to last a few hours. The battery voltage / charge relationship is not linear. At the nominal voltage 3.7V large changes in charge only give small changes in the battery’s measured voltage. As a rule of thumb charge the unit if the battery voltage is 3.7V or less.

The batteries can also ‘self discharge’ or go ‘flat’ over a few weeks – this is normal if the unit is left for a few weeks it will need a full charge before using. After a day’s use it will only need a few hours charging. Always allow time for an overnight charge if you haven’t used the unit for a few weeks.

When powering up the TAR-3 check the battery status. If the voltage is too low, a warning is displayed and the unit should be recharged (TAR-3 units will power down after 20 seconds). If during use the battery voltage drops below 3.7V, 'BAT' is displayed at the top right-hand corner of the LCD display. The unit will still function until the end of the grid.

It depends on usage and how long you use the unit per day. All batteries fitted by us are guaranteed for two years. In our experience the batteries fitted in a unit used two or three days per week for six to eight hours and charged before each use will last over five years.

Yes. See (Downloaded on April, 9th, 2020) (Downloaded on September, 8th, 2016) and… (Downloaded on December, 10th, 2020)

The TAR-3 contains two 9.5Wh Li-Ion batteries that are fixed in position in a tough plastic case. Net weight 50g each. A TAR-3 may be carried in hand luggage or in “check-in” (hold) luggage.
The DFG-1 contains One 20Wh Li-Ion twin cell battery that is fixed in position in a tough plastic case. Net weight 100g. A DFG-1 may be carried in hand luggage or in “check-in” (hold) luggage.

We ship the DGF-1 and TAR-3 according to :

'Section II in Packing Instructions 967 and 970' for UN3481. We are not required to attach a 'lithium battery mark' to the packaging. We may attach a UN3481 label if asked to do so by the shipping company.

WARNING Do not crush, heat, incinerate, short circuit, dismantle or immerse in any liquid that may vent or rupture the batteries.

No. The built in charger stops charging when the batteries are fully charged. Leaving the charger on charges the batteries and then enters maintenance mode. During the following weeks or months the charging circuit monitors the voltage of the batteries and will charge them as they self discharge. It is not recommended, or environmentally friendly, to charge the unit for long periods (weeks) as the external USB supply will consume energy and the TAR-3 unit consumes around 150mW when in standby mode during charging.

The our TAR-3 and DFG-1 use two two LI-ION 3.7V 2600mAh battery cells with a charge voltage of 4.2V; fully discharged at 2.75V and a nominal capacity of 2600mAh each.

N.B. The operational temperature for Li-Ion batteries is -20C to +60C but the temperature range for charging is zero Celsius to +45 Celsius. Do not charge in freezing conditions!

No! Opening the unit will invalidate your warranty! If your unit is still under warranty contact us as the batteries are covered by our warranty and we will replace them. If your unit is out of warranty then we recommend that you return it to us. We will check your unit and update the software if required. During battery replacement we will also replace the waterproof seal. Replacing the batteries is not for the fainthearted as the batteries are sealed in place with a specialist silicon sealant (NOT bathroom sealant) and the terminals are soldered to the circuit board using resin free solder to prevent corrosion. Using the wrong solder or sealant can reduce the life of your unit and will reduce it’s performance. The circuit boards are lead free and require solder that most users do not have. A low wattage, temperature controlled soldering iron is also required. It is unlikely that most users have access to the correct equipment.

The units may be recharged at any time. Li-Ion batteries do not have a 'memory' like other rechargeable batteries and the built in charger will charge and then maintain the charge in the batteries without damaging them.

Batteries that have been left for several months or a year or more and have completely self discharged will take ten hours to charge. After a day’s normal use the TAR-3 will typically require four and a half hours charging (or less).

The DFG-1 uses much more power than the TAR-3 and takes eight to ten hours to recharge.

The battery can be recharged with any USB power supply or port. Our TAR-3 and DFG-1 products have a built in Li-Ion battery charger and only requires a five volt 500mA supply. Any USB power source can be used.

  • A mains USB supply,
  • a USB hub,
  • a 12V car to USB 5V adapter, or
  • a standard USB port.

How long is a piece of string? The battery life depends on many factors. Tests have shown that the TAR-3 can take one measurement per second for over eighteen hours, over sixty-five thousand readings or one hundred and sixty 20m by 20m grids. That’s a lot of readings!

The DFG-1 battery lasts for twelve hours after a full charge. You can attach a 'Power Bank' and charge the battery while using the DFG-1

The exact battery life will depend on;

  • the ambient temperature,
  • the age of the batteries, and
  • the rate of measurement.

Lithium Ion Batteries should NOT be charged when the temperature is below zero degrees Celsius (when it is freezing).

Yes, USB Power Packs can be used to charge the DFG-1 and  TAR-3  - just like mobile phones and tablet devices!

Note You can charge and use the DFG-1 at the same time, but you cannot charge and use the TAR-3 at the same time

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SD Card and Results

The SD Card and results are compatible with Microsoft Windows (XP to 10 and 2012) including mobile versions, RT and Phone. Results can also be transferred to Android, Linux, and *BSD based PCs, tablets and phones. Apple PCs, phones and devices are also seamlessly supported! The results are stored in a plain text file containing only ASCII characters

You do not need a cable to transfer your results are transferred between the meter and your PC without having to install any software, drivers, and without cables. No "Com" ports are required!

Some files contain binary data and are for the internal use of the unit. Only. *.TXT files are in plain text (ASCII) and can be opened (or imported) by many programs. The *.SET files are used by the unit to store setting information and should not be changed. DAT files are binary files containing your results. When using the TAR-3's 'Line Mode' the *.DAT file contains the results ready to use with RES2DINV.EXE. The *.SWP file contains binary data - you cannot read the contents.

No. We do supply replacement parts, but any card will work

New cards need to be formatted with a FAT32 file system and initialised before they can be used. Most cards are supplied formatted with a FAT32 file system but most cameras reformate the card with an incompatible file system. The card will work with the TAR-3 and can be used by most PCs and Tablet devices after formatting and initialisation using a PC. The FAT32 file system is propriety and owned by Microsoft©

No. Units are supplied with a Micro SD Standard capacity card with a Normal Speed (NS) rating. Should the SD card be damaged it can be replaced with readily available replacements.

Don't panic!

The memory card socket is a "Push/Push" socket. To remove the card push it in until you here a "click" the card will then be pushed out of the socket by an internal spring. The card socket has an "anti-flyout ramp" which prevents the card flying out and getting "lost" in the case. Once pushed and allowed to spring out the card can be removed.

If you switch the unit off in the middle of a grid the results for that grid are lost. Saved and completed grids are unaffected. If you "End" the grid the results are saved and the unit powers off.

Results are transferred between the meter and your PC without having to install any software, drivers, and without cables. No "Com" ports are required!

Results are available in plain text comma separated values (CVS) format and can be viewed or edited without specialist software. The results can be edited using Windows Notepad, Word, Excel, Vim, or OpenOffice.

Our products use standard Multi Media or Secure Digital memory cards. The same type used in your camera or phone. You can swap cards between grids allowing results to be analysed while continuing to take readings. Swapping cards allows results to be "archived" without the need for a PC. You can copy results to your phone, camera or tablet. We recommend cards of one, two, four or eight gigabyte you do not need to use high speed cards.

The TAR-3 displays the resistance in Ohms. The resistance is calculated using the current flowing between C1 and C2 and the voltage measured across P1 and P2. This is the raw, or apparent, resistance. It does not take into account the geometry of the probes ie Weiner or Twin probe arrays.

The data files are in plain text with a header and the data in Comma Separated Value (CSV) format. Please let us know how you want the data to be formatted. We have a library of scripts that can manipulate the data into any format!

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Common Features

No. Setting are saved automatically and reloaded on power up. The settings can be returned to their factory default value by the user.

This is normal. Status messages are written to the screen during normal operation and updates or clears them when the unit starts a new step. During startup the unit goes through its startup tests and displays the current status message. When the test is completed a new message is displayed. For example, during start up the MMC Memory Card's File Allocation Table is checked and initialised. During this process the LCD will display "MMC FAT Init" (Please wait). If the control unit "hangs" at this point it means that the Multi Media (Secure Digital) Memory card is missing, faulty or incorrectly inserted in the card reader. When the card is inserted the message is cleared and the unit will continue.

There are two sets of five buttons on the front of the unit and one button ON button just below the LCD display and an OFF/Reset button under the access cover.

Switches the unit OFF and resets the unit. (Located underneath the access cover next to the USB charging connector)

On the top of the meter (below the LCD Display), powers the unit up.

The two sets of five buttons allow the user to operate the unit with either their left and/or right hand.
Our products are "Menu Driven" in that the option groups are scrolled through and the desired options selected. The groups options can then be scrolled through and the required setting selected. The selected setting can then be changed - Increased or Decreased before it is Selected or Entered. Back/Previous/Up Button Increase Button Enter/OK/Select Button Decrease Button.

RM Frobisher aim to produce reliable equipment at affordable prices. To do this we manufacture in volume and try to have a stable product design. This helps us maintain quality and our competitive prices. Our software is thoroughly tested and has the functions required to carry out surveys accurately and reliably. We recognise that our products donot do everything (they are not designed to) but if you have a request for a feature that would be useful to many users please let us know. The unit may already have the capability or it may be possible to incorporate it in updates.

Yes! We do. Unfortunately (or fortunately depending on your point of view) when products work as expected, just like the last time it was used, users do not ask questions or contact us. We would love to share users' experiences. Please send us a link to your work or website.

The LOAD DEFAULTS option replaces all of the user settings with the factory default values. This is how the equipment is supplied. Users cannot change the default values (they are fixed when the unit is manufactured).

When the unit powers up it checks the SD Card for completed GRIDS and sets the GRID No. to the first unused GRID No. - You can only delete data files using a PC.

Yes! RM Frobisher (1986) Ltd' meets or exceeds the current guidelines. You can download a copy here

This is normal. When running the unit writes information to the screen almost continuously. Most of the messages are overwritten before they can be seen - every milli-second (mS) or so. Some information may take longer to overwrite and be displayed for tens of mS. Writing the results to the SD/MMC card is relatively slow and formatting a SD or MMC card can take up to thirty seconds. The information written to the screen is the current status message

The two line LCD Display used on the TAR-3 was selected in preference to a colour LCD display because it has a low power consumption, which extends battery life, it's usable in bright sunlight and readable over a wide range of viewing angles.

Words in all capitals like "ENTER", "BACK" and "SAVE" use the same capitalisation as used on the LCD display. Words in capitals are selectable options . Words that have an initial capital letter or contain one or more capitals are used in a restricted manner and can be found in the glossary.

The Cursor is only visible when the TAR expects an input from the user. The Cursor is not visible when the TAR-3 is taking a measurement or writing data to the Memory Card.

The LCD Cursor is the black flashing rectangular box on the LCD display.

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