Geonics EM61-MK2

Overview

EM61-MK2A (lower coil and shorting plug)

The EM61-MK2 is a time domain metal detector used to locate ferrous metals. Most often, it is used to locate unexploded ordnances, also known as UXOs, at armories although it can be used for other applications such as utility locating and searching for underground storage tanks. A highly sensitive instrument with great resolution, the EM61-MK2 can find a 55 gallon drum can be detected at depths of over 3 meters!

The user can pull or push the EM61-MK2 as it records data from three or four, user-selected time gates. These time gates measure the response decay rate, supporting both the characterization and limited discrimination of targets. Typically, target responses result in a large defined peak.

EM61-MK2 Configurations

The EM61 comes in a variety of configurations. The original EM61 configuration, the EM61-MK2, requires the user to wear a backpack. Its coil is made of fiberglass. While purely anecdotal, the original fiberglass coils seem to be the most stable units when performing static back ground tests.

The EM61-MK2A, known as the army designation, improved on the original EM61-MK2 configuration in that its battery and electronics mount inside of the coil instead of on a backpack worn by the user. Therefore, the operator need not lug the electronics on his or her back. Further, resin encapsulates the coil, making it more watertight.

The EM61-MK2HP (high power) modification to the EM61 boosts its power and signal. The EM61-HP uses a much larger battery and increases the signal of the standard EM61 coil by eight times and will increase the response by 45 to 80% depending on the size of the target.

The EM61HH-MK2 (hand held) is different than the other EM61 units in that uses a 17cm round coil on a staff as opposed to the 0.5m x 1.0m rectangular coil used by the other EM61s. The user must wear a backpack with the electronics and battery like the EM61-MK2. The staff can be carried by strap or mounted on a wheel set. The EM61HH-MK2’s smaller coil allows greater sensitivity to smaller objects that are shallow. For example, a single 20mm projectile can be detected to a depth greater than 0.5 m. If one wants to compare it to the EM61-MK2 and EM61-MK2A, a 55 gallon drum can be detected at a little more than 2 meters.

EM61-MK2 Towed Arrays

Multiple EM61-MK2, EM61MK2A, and the EM61-MK2HP units can be connected together to create an array for larger coverage over a survey area. These arrays are often 3 units (1 master unit and 2 slaves) and are towed behind a vehicle. Besides a cable connecting the electronics together to work in unison, often a power cable is included to power all three electronics from one deep cycle battery.

EM61-MK2 Considerations

Before renting, customers needs to decid what configuration (or if a towed array) will be best suited for their target. In addition, they should decided whether they need to measure 3 or 4 time gates. If they only need three, they may decide to run a bottom coil with shorting plug instead of using both a top and bottom coil.

Individual EM61 units can be run in auto, wheel, or manual mode. Automatic mode means the instrument is run in free mode and collects data at a user selected rate per second. This can be good for searching areas or used in conjunction with a GPS antenna. Wheel mode uses an odometer to trigger readings. Although seldom used, some prefer wheel mode when performing a survey with line and station numbers. Manual mode is used with a trigger located on either the data logger cable or electronics. All EM61 renters are assumed to be using the auto mode unless they specifically request a wheel set with an odometer or data cable with a trigger.

When renting an EM61, it is imperative to manage batteries. EM61s are extremely sensitive to voltage stability and decay. Further, customers inadvertently under charge EM61 batteries. All EM61 batteries from geonicsrental.com are 12volt, 12 amp hour batteries. This means that depending on the charger’s amperage that the the battery will take 6-12 hours to fully charge.

Typical EM61 Packing List

1 x Electronics Assembly (Back Pack or A type)
1 x Upper Coil Assembly (if requested)
1 x Lower Coil Assembly
4 x Coil spacers (if upper coil is requested)
1 x Shorting plug (if only using a lower coil)
1 x Cable (connect upper and lower coil)
2 x Cable (lower coil to electronics assembly)
2 x Cable (electronics assembly to data logger)
1 x Handle
1 x Trailer Kit (two wheels)
2 x Battery Packs for EM61
2 x Battery Chargers for EM61
1 x Data Logger
1 x Battery Charger for Data Logger
1 x Flash Card Reader
1 x USB Flash Drive with Manuals and Software
1 x GPS Mount (if requested)
2 x Shipping Cases*
*EM61 MK2A Coil Box (43x26x14, 115lbs) – most often provided with “A” configuration
*EM61 MK2 Coil Box (43x26x10, 100lbs) – most often provided with original configuration
*Wheel Box (23x23x23, 85lbs)

Dimensions and weights will vary depending on contents of specific orders.

User Manuals

EM61-MK2 and EM61-MK2A Specifications

Bottom coil: Air-cored coil, 1 x 0.5 m in size, coincident with EM source
Top coil: Air-cored coil, 1 x 0.5 m in size 28 cmabove main coil
Maximum Output: 10 000 mV
Dynamic Range: 18 bits
Time Gates: Four gates of bottom coil response only, centered at 256, 406, 706 and 1306μsec; or, three gates of bottom coil response at
256, 406 and 706μsec, with one gate of top coil response at 706μsec, after T/O time.
System Controller: Allegro field computer with 486 AMD processor, 24-line LCD display with 40 characters per line.
Acquisition Speed: Up to 16 records (4 time gates per record) per second
Data Storage: 24MB solid state memory for up to 1,000,000 records; extended memory, optional
Power Supply: 12 V rechargeable battery for 4 h continuous operation
Operating Weight & Dimensions:
Backpack: 8 kg; 60 x 30 x 20 cm
Coil Assembly: 14 kg (23 kg trailer mode)
Bottom: 100 x 50 x 5 cm
Top: 100 x 50 x 2 cm

EM61-MK2HP Specifications

Time Gates: Four gates of bottom coil response only, centered at 261, 376, 527 and 727 μs; or, three gates of bottom coil response at 261, 376 and 527μsec, with one gate of top coil response at 527μsec, after T/O time.
System Controller : Allegro field computer with 486 AMD processor; 24-line LCD display with 40 characters per line
Acquisition Speed: Up to 16 records (4 time gates per record) per second
Data Storage: 24 MB solid state memory for up to 1 000 000 records; extended memory optional
Power Supply: Two 12 V/16 Ah rechargeable batteries or 12 V/10 Ah rechargeable battery (for low power operation only)
• 2 h continuous operation in full power mode
• 7 h continuous operation in low power mode
• 2 h continuous operation in low power mode (small battery)
Operating Weight & Dimensions:
Backpack: 21 kg; 60 x 30 x 20 cm
Coil Assembly: 14 kg (23 kg trailer mode)
Bottom: 100 x 50 x 5 cm
Top: 100 x 50 x 2 cm

EM61-MK2HH Specifications

Time Gates : Four gates of bottom coil response only centered at 147, 263, 414 and 613μs; or three gates of bottom coil response at 147, 263 and 414μs with one gate of top coil response at 414μs sec after turn-off time
System Controller: Allegro field computer with 486 AMD processor, 24-line LCD display with 40 characters per line.
Acquisition Speed: Up to 16 records (4 time gates per record) per second
Data Storage: 24MB solid state memory for up to 1,000,000 records; extended memory, optional
Power Supply: 12 V rechargeable battery for 4 h continuous operation
Sensor Size: 33 x 20 cm
Wheel Mode Resolution: 0.1 or 0.2 meters, switch selectable
Weight:
With wheels 7.5 Kg
Without wheels 2.8 Kg
Length:
Minimum 130 cm
Maximum 180 cm