Freelance Gephysical Consultants Ltd

SAMPLE HARDWIRED SIMILARITY ANALYSIS


SERCEL VE464 and PELTON VIBPRO HD VCU DATA

Freelance Geophysical Consultants Ltd.can remotely fetch and analyzed hardwired similarity data from Sercel VE432, VE464, Pelton HD, etc and provides with full comprehensive report about the performance of each vibrator and the timing differences.

• VibPro/Encoder – The sweep generator located in the recorder responsible fortransmission of the timing sequence, generation of the correlation pilot and output ofthe vibrator attributes transmitted from the vibrator electronic, via radio, at thecompletion of each sweep.

• VibPro/Decoder – The vibrator electronics located in each vibrator responsible forgenerating the vibrator reference and controlling the ground force. This unit alsocalculates performance attributes which are transmitted back to the recorder at thecompletion of each sweep.

• Correlation Pilot – Signal generated in the VibPro/Encoder and recoded on anauxiliary channel and used for correlation of the seismic data.• Vibrator Reference – Signal generated in the Vibpro/Decoder and used to controlthe vibrator ground force during the sweep.

• Baseplate Signal – Signal recorded by an accelerometer mounted on the vibratorbaseplate.

• Reaction Mass Signal – Signal recorded by an accelerometer mounted on thevibrator mass.

• Weighted Sum – The calculated signal used to approximate the actual vibratorground force on the earth. It is calculated by multiplying the mass of the baseplateby the baseplate acceleration and summing it with the product of the reaction massacceleration and the mass of the reaction mass.

• Hardwire – Similarity test used to compare the vibrator output with the correlationpilot. All signals coming from the vibrator are recorded through line electronics.• Taper – Region of the sweep where the amplitude varies from 0 to the maximumand generally is based on a cosine function. Pelton defaults to a cosine taper.

The start time betwen each vibrator should not exceed more than 50 microseconds and thisis measured between the vibrator reference with the correlation pilot.

On a vibrator, seven signals are especially of interest:- Signals from the sensors:

- Macc : Mass acceleration

- BPacc : Baseplate acceleration

- MLVDT : Mass LVDT

- VLVDT : Valve LVDT

- The command : TM (Torque Motor current)

- The resulting signal and the reference:

- GF : Ground Force (Massmass „e Macc + MBP „e BPacc)- Ref : Pilot signal

All these signals can be accessed using Birddog Box or Sanwich Box and/or internal recorder capabilities.

With Sercel VE432 and VE464,the Reference is the signal used by the DSD to generate the Ground Force.system. The Ground Force is based on the Mass acceleration and Baseplate acceleration.

The Baseplate acceleration is usually weak at low frequencies and increases with the sweep frequency. The Mass acceleration, for its part, is quite constant.The acceleration signals are derived from the Torque Motor signal (TM).


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