7.Dpg master slave operation
See note (*)
A convenient way of reducing the cost of field operations consists of using two recording trucks in parallel, recording a greater number of traces without increasing the number of vibrators. One recording truck is used as "Master" and the other as "Slave".
Each recording truck is equipped complete with an acquisition system and a DPG.
One of the recording trucks is used as "Master" unit and the other as "Slave".
The DPG in the Master unit does not only perform the standard function (controlling all DSDs and generating a reference signal), but it also controls the DPG in the Slave unit.
The DPG in the Slave unit needs to be configured with the "DPG-Slave" software (PCMCIA card). It is then seen as a DSD from the Master DPG. Once the "DPG-Slave" software is loaded into a DPG, the function of the Slave DPG consists of generating a reference pilot signal synchronous with the Time Break. A Slave DPG does not control any DSD.
An example of Master/Slave configuration is shown on next page, involving two recording trucks.
The Slave DPG receives a DSD-like address (#29 to 32) from the Master DPG. Once addressed by the Master DPG, the Slave DPG acts as a DSD. It receives the t0 parameter and t0 Sync from the master DPG. On the first correct reception of a t0 parameter, the DPG generates a relay contact closure (EXTGO signal). This relay contact closure is used in the recording truck to start the recording.
The time denoted T on the timing diagram may vary from one recording system to another.
In order to keep the time between the Firing Order and the Time Break to a minimum, and to cause the Slave recording truck to initiate the 'Waiting for TB' sequence just before the Sync is decoded, giving rise to the TB, you may need to adjust the number of T0 parameters to be transmitted, by modifying the 'T0 Repeat time' parameter. Try different values until the best possible cycle is achieved.
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8.Navigation
The navigation is an option that can be implemented on the VE432. The two new operation modes are shown in the options setup of the operation environment:
- Slip Sweep navigation
These two options require a stack of one, the input of the SPS S file, and a DGPS in each vibrator.
8.1Implementation
A license free microwave radio (2.4 GHz, 200m range) needs to be installed in each vibrator that allows communications within a fleet.
The DSDs need to be slightly modified:
- A modified NAV plug need to be installed and connected to the DVC board's Ethernet socket inside the DSD.
- A cable connects the microwave radio and the DGPS to the NAV plug.
In each fleet, one microwave radio needs to act as a master (an external switch allows this), usually the one of the leader.
With this option, as soon as the leader is ready (pad down), it queries each of the other DSDs in the fleet to see if they are ready using the micro wave radio. When they are ready, they send their GPS position to the leader. As soon as all the vibrators are ready, the leader computes the COG of the fleet and sends this location with the ready message to the DPG.
The DPG relays the message to the SN388 HCI that displays the location of the fleet in the Positioning environment (see the example below). This allows the system to identify this location and to shoot automatically the corresponding VP. VPs can be shot in any order by any fleet.
In the operation environment, there is no delay to setup, and the GO button remains gray until the ready is received. Everything is started at maximum speed.
Example of fleets display before acquisition is launched in the
positioning environment in navigation mode.
With no DSD network, the fleet location displayed correspond to the
location of the leader vibrator.