Ohmega Ω USER'S MANUAL - Allied Associates Geophysical, Ltd.
Contents
1. J 1Eo Associates G E O P H Y S ICAL L IMITED A Ohmega Q Resistivity Meter USER S MANUAL Concept House 8 The Townsend Centre Blackburn Road Dunstable England LU5 5BQ Tel 44 0 1582 606 999 Fax 44 0 1582 606 991 e mail info allied associates co uk Allied Associates Geophysical Ltd Ohmega 2 WARRANTY 1 Allied Associates Geophysical Ltd AAGL products are fully tested in our workshop both during construction and after completion and are dispatched in full working condition Instruments are guaranteed for 12 months from the date of dispatch from the factory liability being limited in accordance with clause 9 of the General Conditions for the Supply of Plant and Machinery for Export UN Economic Commission for Europe Geneva 1953 2 When unpacking please check the contents against the packing list and inspect for damage and malfunction of any kind In the case of any defect inform the carrier immediately and report in full to AAGL or their local agent the extent of the damage Await their reply before taking any further action except in exceptional circumstances 3 Should a fault be identified that cannot be remedied on site within the guaranteed period consult with AAGL Normal procedure will be to return the unit or complete system if necessary carriage paid to AAGL for inspection and repair or replacement free of charge provided the fault has not been due to misuse 4 As far as pos2. in Fig 4 a mA a Volts b Time Fig 4 The OHMEGA Q SIGNAL a Transmitted signal variable Periodicity b Received signal Here the attenuated and modified signal is superimposed on slowly varying earth currents It is sampled over times A B and C Ohmega Manual Rev E 0506 Page 11 Allied Associates Geophysical Ltd Ohmega 2 The on period is sampled for only the last 4 5 of the on time e g 0 8s in 1 0s An example of the received signal in the presence of electrical ground noise is shown in Figure 3b This figure also illustrates the processing technique used to extract a value of the required potential difference from the received signal here shown superimposed on a slowly varying earth current The signal is digitally sampled over times A B and C and the amplitude calculated as Va Vc 2Vb 4 The on off ratio is 2 5 1 and the sample unsampled ratio during any ON period is 4 1 This is to allow any coupling and IP affects to die away before sampling takes place When a number of cycles are averaged the microprocessor calculates the potential difference from successive sets of three ON periods ABC BCD CDE giving values Vat Vc 2Vb 4 Vb Vd 2Vc 4 etc When conditions are adverse e g a low signal ground noise ratio apparent as a lack of consistency in the readings use higher current settings that do not cause a GAIN ERROR and average over 16 cycles Gain errors are usual
3. 06 999 Fax 44 0 1582 606 991 e mail info allied associates co uk Ohmega Manual Rev E 0506 Page 15 Allied Associates Geophysical Ltd Ohmega 2 CERTIFICATE OF CONFORMITY Product ALLIED OHMEGA earth resistance meter Serial NO oo ccc cece eee eeeeeee Date of Shipment cece cece cece scene sean eeae ees EMC 89 336 EEC Generic EN50081 1 Light Industrial Emissions EN50082 1 Light Industrial Immunity Tests Applied BSEN 55011 Class B Radiated Emissions BSEN 61000 4 4 Fast Burst Transients to Level 2 Light Industrial BSEN 61000 4 2 Static Discharge to Level 2 Light Industrial Category 3 PASS BSEN 55011 Class B Conducted Emissions N A battery only Low Voltage Directive 73 23 EEC N A below 50V AC Machinery Directive 98 37 EEC N A no moving parts We on behalf of Campus International Products Ltd confirm the Product described above meets the requirement in all respects Allied Associates Geophysical Ltd Concept House 8 The Townsend Centre Blackburn Road Dunstable England LU5 5BQ Tel 44 0 1582 606 999 Fax 44 0 1582 606 991 e mail info allied associates co uk Associates PHY SICGAL LiMt TE D Ohmega Manual Rev E 0506 Page 16 Allied Associates Geophysical Ltd Ohmega 2 Alllied Associates Geophysical Ltd USER MANUAL COMMENTS SHEET Please note on a copy of this form any suggestions for improvement or any errors found in this manual Please return the f
4. 0Q 7 Select the number of readings to be averaged using the Cycles button This will depend to a great extent on ground noise Start with 4 readings and increase or decrease depending on the consistency of the readings obtained 8 Select Resistance and press the GO button The display will initially indicate the voltage gain being used in the measurement setting Gain GS Anes Baa G 5 indicates the amplifier gain setting These are x5 x0 5 x0 05 and x0 005 Ina noisy environment high and varying SP values may cause the amplifier to saturate during the averaging The display will show GAIN ERROR Change Cungu Ohmega Manual Rev E 0506 Page 10 Allied Associates Geophysical Ltd Ohmega 2 In this case reduce the current to bring the signal within the operating range The display will then indicate the successive averages of the resistance bleeping each time during the process At the standard setting the instrument takes 2 15 to complete a set of 4 readings A three figure resistance will show with the decimal point approximately placed followed by Q or mQ If the potential and current connections have been incorrectly connected a negative sign will precede the digits This can also be due to ground conditions 9 If the switching circuits operated by the current or mode buttons on the top panel are faulty the display will read MODE ERROR 2 4 THE SIGNAL The transmitter uses commutated DC to produce the signal shown
5. 1 0 5mA Cycles 2 3 Check battery volts If the battery is below the operating voltage the display will read BATTERY LOW Reduce Current Ohmega Manual Rev E 0506 Page 9 Allied Associates Geophysical Ltd Ohmega 2 4 If the external temperature is above 40 C or below 0 C take steps to bring the temperature within the operating range Check the temperature regularly since in tropical sunshine it may well rise above the danger level Note that although the instrument will operate below 0 C it is not designed for work under exceptionally low temperature conditions 5 Check the SP voltage Use the MODE switch to put the instrument into the Self Potential mode Make a few measurements to see how it is varying by pressing the GO switch and noting the results obtained The amplitude and rate of change of the SP will affect the readings at low resistance values and determine the instrument settings required to optimise accuracy 6 Select the current setting using the mA button Normally start at 2mA and keep as low as possible consistent with obtaining good repetition If ground conditions are such that the instrument cannot deliver the required current or there is an open circuit it will read CURRENT ERROR Check Electrodes Decrease the current and or water the electrodes to improve ground contact Experience shows that when operating multicore cable systems accurate measurements are obtained with contact resistances below 200
6. ABLE Bedfordshire England LU5 5BQ Printed in Great Britain Ohmega Q is a registered trademark of Allied Associates Geophysical Ltd Ohmega Manual Rev E 0506 Page 3 Allied Associates Geophysical Ltd Ohmega 2 WARRANTY 2 CONTENTS 4 i GENERAL DESCRIPTION OF THE OHMEGA Q RESISTIVITY SYSTEM 5 1 1 The Ohmega Q 5 1 2 Power Booster 5 2 THE ALLIED OHMEGA Q 6 2 1 Construction 6 222 The Controls and Connections 6 2 2 1 ON OFF Switch 7 2 2 2 GO button 7 2 25 mA current button 7 2 2 4 MODE button 7 2 2 5 Number of Cycles 8 2 2 6 Sample Time 8 2 2 7 Alpha Numeric Display 8 2 2 8 External Power Supply 9 2 2 9 Manual Control 9 2 2 10 External System Connection 9 2 3 Making Measurements 9 2 4 The Signal 11 2 5 Power Supply 12 2 6 Battery Charger 13 2 7 Instrument Parameters 13 3 OHMEGA SPECIFICATIONS 14 4 i EC CERTIFICATES OF CONFORMITY 15 D USER MANUAL COMMENT SHEET 17 Ohmega Manual Rev E 0506 Page 4 Allied Associates Geophysical Ltd Ohmega 2 GENERAL DESCRIPTION OF THE SYSTEM 1 1 THE OHMEGA Q The OHMEGA Q is a high quality earth resistance meter capable of accurate measurement over a wide range of conditions lt has a maximum power output of 18 watts manual selection of current in steps up to 200 mA a choice of sample time signal length averaged and three frequency settings The receiver incorporates automatic gain steps which provide a range of measurements from 0 001Q to 360kQ The instr
7. DE and mA buttons are pressed simultaneously the sample time or signal length can be changed as shown below APLHA NUMERIC DISPLAY The 80 character 4x20 liquid crystal display indicates the parameters selected and the measurement details as the survey progresses See Figure Three The display can be backlit by pressing Mode and Cycles simultaneously The light automatically switches off after one minute if no activity is sensed during this time Fig 3 Ohmega Q Display and Electrode Terminals Ohmega Manual Rev E 0506 Page 8 Allied Associates Geophysical Ltd Ohmega 2 EXTERNAL POWER SUPPLY An external 12V power supply may be connected through the socket Chrg Ext See Fig 5 A connecting lead is supplied for this purpose It is important to remember the correct polarity when connecting to an external supply n EA Do not connect to a car battery while itis being charged MANUAL CONTROL The red and black coloured current and potential terminals marked P1 P2 C1 C2 are situated on the front panel See Figure Three Single core cables may be connected to these terminals for measuring earth resistance 2 3 MAKING MEASUREMENTS 1 Check that the instrument is correctly connected to the current and potential cables See Fig 7 When the manual Offset Wenner system is used the current and potential terminals are connected to the Offset Wenner system switchbox 2 Switch on Display shows MODE Resistance
8. ig 2 Two OHMEGA Q front panel showing Operation Buttons Ohmega Q Manual Rev E 0506 Page 6 Allied Associates Geophysical Ltd Ohmega 2 All the external controls together with the liquid crystal display are situated on the top front panel of the instrument They are fully waterproof The controls are shown in Figure 2 and are described below In addition to the ON switch and the GO or initiate measurement button there are three other buttons marked mA Mode and Cycles See Figure 3 ON OFF Select to switch the instrument for operation or to switch the instrument off GO Press this button to start measuring with the previously set parameters mA Current The button marked mA is used to select the desired current in milli amps The current is increased each time the button is pressed in the following steps The current value selected is indicated on the display MODE The button marked MODE selects the type of measurement The display will indicate the following sequence of options as appropriate Resistance Self potential Battery Volts Ohmega Manual Rev E 0506 Page 7 Allied Associates Geophysical Ltd Ohmega 2 NUMBER OF CYCLES The button marked Cycles selects the number of readings to be averaged This can be from 1 to 16 Details of how the signal is processed to obtain a single measurement of ground resistance are given in Section 2 4 of this manual SAMPLE TIME If the MO
9. ly due to sudden increases in ground noise saturating the system If the area is generally very noisy it may be necessary to operate at the longest cycling time In extreme conditions i e measuring very low resistances against a background of large amplitude and varying SP highly inconsistent readings may be obtained In this case it is necessary to put the instrument into the computer command mode and vary the sampling parameters until satisfactory results are obtained See Section 3 2 5 POWER SUPPLY The Ohmega Q uses sealed gel cell batteries 7 AH at 12V Under average working conditions e g 10 offset soundings per day at 5mA recharging every 2 working days would be safe practice Electrical imaging uses more drain on the batteries and so the instrument should be charged overnight during survey operations Should it be necessary to be away from a mains power source for more than a few days the instrument can be operated using an external supply A 12V car battery which can be recharged from a vehicle can be used in an emergency A separate lead is supplied which can be clipped is onto the battery Be sure to check the polarity before connecting to the instrument Do not run the vehicle engine while the instrument is connected to the battery as transients from the alternator can damage the transmitter circuitry Ohmega Manual Rev E 0506 Page 12 Allied Associates Geophysical Ltd Ohmega 2 2 6 BATTERY CHARGER Thi
10. orm to Graham White Alllied Associates Geophysical Ltd Concept House Blackburn Road DUNSTABLE Bedfordshire LU5 5BQ ENGLAND Manual Title Rev Number Comments Ohmega Manual Rev E 0506 Page 17
11. pply GENERAL Weight Electrode capacity Allied Associates Geophysical Ltd Concept House 8 The Townsend Centre Blackburn Road Dunstable England LU5 5BQ Tel 44 0 1582 606 999 Fax 44 0 1582 606 991 e mail info allied associates co uk Ohmega Manual Rev E 0506 18W 0 5mA to 200 mA 8 45 4 25 2 85 1 to 16 O 180V with auto gain averaging 22MQ 360KQ 0 0010 80 character alphanumeric liquid crystal Rechargeable sealed gel cell 7 AH 12V 6kg 2 Current 2 Potential Page 14 Allied Associates Geophysical Ltd Ohmega 2 CERTIFICATE OF CONFORMITY Product Charger for ALLIED OHMEGA Q earth resistance meter Serial NO acceca Date of Shipment cc cee eee e sees seen eene ews EMC 89 336 EEC Generic EN50081 1 Light Industrial Emissions EN50082 1 Light Industrial Immunity Tests Applied BSEN 55011 Class B Conducted Emissions BSEN 55011 Class B Radiated Emissions BSEN 61000 4 4 Fast Burst Transients to Level 2 Light Industrial BSEN 61000 4 2 Static Discharge to Level 2 Light Industrial Category 1 PASS Low Voltage Directive 73 23 EEC N A below 50V AC Machinery Directive 98 37 EEC N A no moving parts We on behalf of Allied Associates Geophysical Ltd confirm the Product described above meets the requirement in all respects Allied Associates Geophysical Ltd Concept House 8 The Townsend Centre Blackburn Road Dunstable England LU5 5BQ Tel 44 0 1582 6
12. s operates from 240V or 115VAC The maximum current output is such that batteries can be left on indefinitely without suffering any damage Charging time from full discharge is 16 hours If storing the Ohmega Q for a long period of time recharge the battery every month Failure to do so will result in irreversible damage to the battery NOTE if the meter is operated while the battery is being charged the charger is automatically disconnected 2 INSTRUMENT PARAMETERS The suggested values below have been selected to produce measurements with the minimum of power The operator can increase the speed of the survey by reducing the current on time to 1 second or less If this is done it is likely that the current will have to be increased to 1 2 or 5 mA depending on the electrode spacing used If unstable measurements are obtained the current should be increased In low resistivity conditions the current should be increased further Check the waveform to make sure that a good voltage signal is being detected In noisy conditions either the current on time or the number of cycles should be increased Ohmega Manual Rev E 0506 Page 13 Allied Associates Geophysical Ltd Ohmega 2 ALLIED OHMEGA Q SPECIFICATIONS TRANSMITTER Maximum power output Current range Square wave repetition Number of readings averaged RECEIVER Input voltage range Input impedance Measurement range Low pass filter Display Power su
13. sible use original case and packaging material for return of the instrument Equipment is on occasions subject to very rough handling during transit and AAGL cannot be liable for damage due to faulty packing 5 It is the responsibility of the customer to notify AAGL or their agent of defect or damage to the equipment within a reasonable time of receipt We would recommend that any defect or omission should be notified verbally but with written confirmation no more than 72 hours after receipt of the product 6 AAGL Associates Geophysical Ltd will take all necessary steps to rectify any failure which is deemed the responsibility of the manufacturer as quickly as possible 7 No liability against consequential loss can be accepted under any conditions Thank you for purchasing the Allied Ohmega Q Resistivity Meter Allied Associates Geophysical Ltd Concept House 8 The Townsend Centre Blackburn Road Dunstable England LU5 5BQ Tel 44 0 1582 606 999 Fax 44 0 1582 606 991 e mail info allied associates co uk Attn Graham White Technical enquiries Attn Norman Bell Sales enquiries Ohmega Manual Rev E 0506 Page 2 Allied Associates Geophysical Ltd Ohmega 2 Copyright 2006 Allied Associates Geophysical Ltd All rights reserved including the right of reproduction in whole or in part in any form Published by Allied Associates Geophysical Ltd Concept House 8 The Townsend Centre Blackburn Road DUNST
14. ument is powered by a large capacity rechargeable battery providing several days of use without recharging in average terrain conditions The OHMEGA Q is housed in an impact resistant steel case 1 2 POWER BOOSTER Starting in AUGUST 2000 the power booster is fitted as standard to all Ohmega Q systems providing current capacity to 200mA Ohmega Manual Rev E 0506 Page 5 Allied Associates Geophysical Ltd Ohmega 2 THE GEOPULSE OHMEGA Q 2 1 CONSTRUCTION The OHMEGA Q is housed in an impact resistant Pelican case and is fully water resistant The various units are mounted below the front panel and the whole instrument can be removed from the case by unscrewing the plate The transmitter receiver controls and display occupy the full area of the instrument front panel The Ohmega Q is supplied with 4 stainless steel electrodes four 100m cables on lightweight reels and a battery charger The design of the Ohmega Q allows for the construction of a basic resistivity meter and incorporation of bower booster now fitted as standard 2 2 THE CONTROLS AND CONNECTORS o Ohmega 2 s Ait4d gt m gt a T v ao Se a aes a eN E p P 4 p e y Ap DaN Ki lt y i 5 TES g ie O On A P k sVe a e s A g ad z EAA ai Taca A 1 4 o gt f 4 ip eee ed 4 yea e Ass eS a g g Mode mA Cycles Go F
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