Using the Geonics EM31

Battery Check

1. Set MODE switch to OPER position and rotate RANGE switch to BA TT position.

2. If meter reads above ±4.4 then batteries are in good condition (C size)

Initial Set-up

1. Using Identifying labels, attach transmitter coil tube.

2. Set MODE switch OPER and cheek the zero reading. Set the RANGE switch to least sensitive position (1,000 mS/m)

3. The tolerance for this test is ±1 mS/s. To adjust reading use the DC ZERO CONTROL, located under front panel. Remove battery pack to gain access to the controls.

4. Turn instrument off and attach receiver coil tube

Equipment Functional checks

1. Set RANGE switch to 100 mS/m. (if reading on the meter is off-scale, i.e. >100 mS/m, set to 1000 mS/m.

2. Set MODE switch to OPER position and adjust the inphase meter reading to zero using the COARSE and FINE COMPENSATION controls. Tolerance +0.1 ppt.

3. To check the phase of the instrument, set the MODE switch to PHASE position. Note meter reading and rotate the COARSE control one step clockwise. If the conductivity meter reading remained the same (tolerance ±0.2), the phase is already correct. Return COARSE control to its original position.

4. If there is a difference in the readings, with the COARSE control in its original position, adjust the PHASE potentiometer about Ľ turn clockwise. Repeat the phase test. If the difference in readings has decreased, repeat procedure or if the difference has increased, the PHASE potentiometer should be rotated counter-clockwise.

5. N.B. Always remember to set the COARSE control back to its original position. This can be confirmed by checking that the inphase meter reads zero with the MODE switch set to OPER.

6. To check the sensitivity of the instrument, set MODE switch to COMP position and rotate COARSE control clockwise one step. The conductivity reading should change between 22 to 26 mS/m.

Operating Procedure

1. Position instrument so that it rests on the hip. Set MODE switch to OPER position and rotate RANGE switch so that the conductivity meter reads in the upper two-thirds of the full range.

Vertical Dipole
Reading panel on top
Effective depth of exploration =6m

Horizontal Dipole
Reading panel is facing horizontally
Effective depth of exploration =3m

Using the Polycorder DL720/31 data logging system

Battery check

Switch on logger and at MODE prompt press 0. Use arrow keys to select BA TTERY, then press Enter

Initial Setup

Switch on logger and at MODE prompt press 0. Use arrow keys to select EM31, press ENTER
SET CLOCK (y/n): N (if yes, the program will abort and you will have to re-run EM31)
FILE: Enter filename (Use Shift keys to select letters)
PHASE Q/I/B: B Select what parameter to record (Quadphase/Inphase/Both)
MODE V/H/B: B Select which dipole orientation to record (Vertical/Horizontal/Both)
ORIENTA TIONS 1/2: 1 Select 1 or 2 orientations to record (different heights or orthogonal)
OPERATOR: Enter operator's name (not mandatory, press ENTER to skip)
COMMENT: Enter comment (not mandatory, press ENTER to skip)
AUTO (Y/N): N Select N for normal operation
LINE: Enter line number, then ENTER
DIR W/E/S/N: Select direction of the line (Conventionally N or S)
START STATION: Enter start station, then ENTER
INCREMENT: Enter station increment, then ENTER (the units here are irrelevant)

CONNECT THE LOGGER TO THE EM31 WHEN EM31 IS IN THE OPER POSITION and Press ENTER to start logging

REVIEW DATA MODE Press 6 (To review previous station information)
COMMENT Press 7 (enter comment then ENTER)
NEXT STN Press 5 (automatically skips a station)
NEW SEGMENT Press 1 (if you have to skip a large section)
NEW LINE Press 4 (Enter line no & Start stn. Enter '-'increment for reverse direction)
MEMORY Press 2 (See how much room is left on logger)
ESC Press ESC (Only use when finished logging)

Downloading the data from the Polycorder to your PC
1. Run DAT31 program on the PC and select COPY FILES FROM POLYCORDER (MOD-720)
2. Set Polycorder to MODE 5-2 and check that:
baud rate = 9600
data bits = 8
parity = N
mating call carriage return (CTRL 0 1 3)

3. Press ESC

4. On PC, Enter filename to store data: - Enter Hxxx file created in logger (CAPITALS), press RETURN

5. Set Polycorder to MODE 2-2 - Select corresponding file on polycorder press ENTER. And then press RETURN on PC.

6. Repeat procedure for Data files (D prefix)

7. Return to main menu (PC) and select CONVERT DL55 TO DAT31 FORMAT. Enter Hxxx filename and both the Hxxx and Dxxx files will be converted to xxx.G31 file format.

8. Use appropriate option to convert to Surfer format

Warning

Do not fill up logger completely with data as this will lead to problems downloading. If there is insufficient memory, delete all unwanted data files. If there is still a problem, delete the EM31 program from logger. When downloading is complete, refer to manual for re-installation of EM31 program.

Last updated by Tim Young (Tim.Young@GeoArch.demon.co.uk) 1st October 1998.