Earth Data PR6-24 Portable Field Recorder Description

The Earth Data PR 6-24 Portable Field Recorder can be used in hostile environments and is ideal for rapid deployment by unskilled personnel. It is suitable for seismic profiling, after shock studies, noise measurements, MT studies and single station micro seismic networks.

140 dB DYNAMIC RANGE

The PR 6-24 incorporates Earth Data’s proprietary 7th order Sigma-Delta technology. This provides a signal to noise ratio of 140 dB at sample rates up to 100 Hz rising to 150 dB at 10 Hz. Even at 1000 Hz the signal to noise ratio is still 130 dB. Data is recorded as 32 bit words to accommodate this high dynamic range.

DUAL SAMPLE RATES

Two sample rates can be selected for recording. When using three channels, these two sample rates can be anywhere between 1 Hz and 1000 Hz. When using six channels, the secondary sample rate must be a simple division of the primary rate. This is useful for real-time monitoring at a low sample rate, whilst recording both sample rates to disk.

As an example, when the primary rate is 1000 Hz, the permitted secondary rates are 500, 250, 200, 100, 50, 40, 20 and 10 Hz.

INTERNAL ARCHITECTURE

The PR6-24 incorporates a 3 or 6 channel digitizer/buffer, a LINUX based rugged PC, an internal GPS receiver and a removable disk unit. All internal units are specified for operation over a wide temperature range. The removable disk unit comprises a 2.5" disk within a weather-sealed housing and incorporates a temperature sensing and heating system which ensures that the hard disk can be operated even with external temperatures of -20 °C. The unit is intended to be used with an external GPS antenna which disciplines the internal time base.

The standard antenna is a 3 V miniature magnetic type. An optional 5 V “bullet” type with a 20 m cable is also available.

FLEXIBILITY

The PR6-24 can be supplied as a 3 or 6 channel unit. The internal digitizer can be directly connected to a radio modem enabling continuous near real-time data transmission whilst at the same time recording to hard disk. Interfaces include real-time serial monitor, serial modem, Ethernet plus optional USB and IrDA. All software and firmware can be remotely updated, avoiding costly return to factory or dismantling.

RECORDING FEATURES

The hard disk, with a minimum capacity of 20 GB allows more than six months of continuous recording of three channels at 100 Hz. Assuming a compression ratio of 2:1 this period can be doubled. When the disk is full the oldest data is normally replaced with new data and at any time the previously recorded data is available by downloading via the Ethernet connection or by simply changing the disk. Disk changes and Ethernet downloads can be undertaken without interrupting the acquisition process.

A comprehensive window recording function allows the unit to remain in low power shut down until the requested time is reached. In addition, an STA/LTA trigger can be used to generate a trigger log file for easy location of events within the recorded data.

Burst mode recording enables high sample rate data to be collected for short periods, whilst recording continuously at a lower rate.

PROGRAMMING THE RECORDER

All recorder parameters are set by an '.INI' file which can be copied to the hard disk from a pre-configured setup prior to deployment or configured during deployment using any web enabled client such as a PDA or Laptop that supports ethernet, usb, bluetooth or wireless lan connection.

The web interface enables channel configuration (such as sample rates), GPS Power mode, GPS Status, Recorded Data files and communication parameters to be set up and monitored whilst the recorder is running to ensure everything is working as intended.

Earth Data provide two Windows based utilities "Modmon32" and "PView" that provide more complex digitizer diagnostic monitoring utilities and recorded data file analysis respectively.