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 ‘Stripe.com’ 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 www.rmfrobisher.co.uk 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.
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.
TAR-3 Resistance Meter
No! There are only two setting the user may have to change:
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 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.
TAR-3 LINE Mode
Yes, they do cost more than NiMH or NiCd but they have less “charge memory” and are more efficient than NiMH when charging 80 to 90 percent 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.
es, 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 relation ship 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 can still function but consider ending the grid and saving the results
It depends on usage and how long you use the unit per day but all batteries fitted by us are guaranteed for two years. In our experience the batteries in a unit used two or three days per week for six to eight hours and charged before each use can last up to five years (or longer).
- http://www.iata.org/whatwedo/cargo/dgr/Documents/lithium-battery-update.pdf (Downloaded on March, 28, 2015)
- http://www.britishairways.com/cms/global/pdfs/lithium_battery.pdf (Downloaded on September, 8, 2016) and
- http://www.dhl.com/content/dam/downloads/g0/express/shipping/lithium_batteries/lithium_batteries_int… (Downloaded on March, 28, 2015)
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.
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 products 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!
Yes – but we don’t recommend it. 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 may 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. If you must replace the batteries yourself, contact us, we will help get you up and running again and we have a list of parts and instructions to help you.
Update (June, 2015)
Having visited sites and seen the equipment available to users (soldering irons, etc.) I recommend that users do not change the batteries themselves! (TA)
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. Both 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.
WARNING Do not charge below zero degrees Celsius (when it is freezing)
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.
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!
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. The card will work with the TAR-3 and can be used by most PCs and Tablet devices after formatting and initialisation.
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 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.
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)
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.
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.
RM Frobisher (1986) Ltd © 2020