Name of System: Crone Pulse EM (PEM).
Method Employed: TDEM (Time-domain electromagnetics) or TEM (Transient EM).
Survey Types:
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· Surface - DEEPEM, Large In-Loop, Moving Loop, Moving Coil - 3 components.
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· Borehole - 3D Borehole PEM - 3 components are measured and oriented.
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· Underground - 3D Borehole PEM - including flat or up-dipping holes.
Measured Quantity: Rate of change of magnetic field in nanoTesla/second (same as nV/m2).
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or magnetic field in pT (with SQUID surface sensor)
Receiver: Fully digital (input is digitized before stacking) with 25 bit dynamic range (150 dB).
Channels (Gates):
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· Typically 20 logarithmic channels in off-time and 1 during ramp (PP).
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· Can read entire ramp and off-time in single sweep.
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· Operator can select from several built-in tables:
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- 10, 20, or 30 chns (single, double, triple density) e.g. 42 channels and PP for 150 msec time base.
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- 45 channels 4.5 usec wide covering the end of ramp and start of off-time.
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- 45 channels 40 usec wide covering ramp and start of off-time.
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- 200 channels user selectable
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· Programmable channel positions in the field.
Stacking: 1 to 32768 stacks with spike rejection.
Gain Control: Automatic software control (no selection or correction required).
Rx Operation: Menu-driven software. Large 16x40 character LCD. Full alphanumeric keyboard.
Display: 256 x 128 pixel scrollable graphic LCD for decay curves and profiles in the field.
Data Handling: Solid state storage; multiple files; all files can be appended at any time.
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Plot, list, sort, delete data. RS232 transmission of all data or only certain files.
Synchronization: Radio, cable, or crystal clock
Current Waveform: Bipolar on-off square waveform with exponential turn-on and ramp off.
Time Base: Off-time plus ramp time.
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· 8.33, 16.66, 50, 100,150 and 300msec for 60 Hz noise rejection
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(equivalent base frequencies of 30, 15, 5, 2.5, 1.67, 0.833 Hz.)
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· 10.0, 20.0, 50.0, 100.0, 150 and 300msec for 50 Hz noise rejection
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(equivalent base frequencies of 25, 12.5, 5, 2.5, 1.67, 0.833 Hz.)
Ramp Time: The time required for the current to turn off.
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· 500, 1000, or 1500 usec selections for precisely controlled linear turn-off ramps.
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· "fast ramp" option turns current off as quickly as possible for a given loop size and current
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(2 usec or less to a few hundred usec).
Transmit Loop:
· Single turn loop of any dimension (less than 100m x 100m to greater than 2km x 2km).
· Multi-turn 14m diameter loop for near-surface Moving Coil surveys.
Tx Output Current:
· 30 Amps max at 160 Volts for 4.8 kWatt system.
· 20 Amps max at 120 Volts for 2.4 kWatt system.
Tx Output Voltage:
· 48 to 240 Volts continuously adjustable for 4.8 kWatt system.
· 24 to 120 Volts continuously adjustable for 2.4 kWatt system.
Tx Safety features: Transmitter automatically shuts off when loop is opened. Also shuts off with high instrument temperature and overload. Fuse and circuit breaker overload protection.
Borehole Probes: 32 mm diameter.
Pressure-tested for depths of 2500m or more.
X, Y components oriented with tilt sensors or 3-axis magnetometer and 3-axis accelerometer.
Operating Temperature: -40°C to 50°C
