The DM24 accepts power from lines in its DATA OUT port. This is a Güralp standard 10-pin combined serial/power interface, a cable for which can be obtained from Güralp Systems. A standard 12V DC power supply is recommended.
The DM24 is configured for use with Güralp Systems feedback sensors, which can be connected directly to the SENSOR A and SENSOR B ports. No further configuration of the sensor is necessary; the input ports carry sensor power, four channels of differential velocity, mass position and calibration signals. The AUXILIARY port allows you to measure and digitize environmental parameters, e.g. local temperature, pressure, or signals from other scientific instruments.
In addition, two pins on the AUXILIARY port allow you to input signals for a fourth, full-rate 24-bit data channel. This channel is digitized continuously, but is interrupted when you calibrate the instrument, so that the DM24 can return the calibration signal on a stream with a different name. When calibration is over, the fourth channel returns to digitizing the external source.
If you prefer, you can attach any seismometer with balanced differential output to the signal inputs of the DM24. You will need to make up a cable to connect the relevant pins of the SENSOR A or B port to your instrument(s). See Section 8.1, page 113, for details of the connector used.
If you have only one sensor, you should attach it to the SENSOR A port, since only this port can be used to send control signals to it (e.g. mass locking and unlocking). The SENSOR B port can therefore only be used for sensors which do not require remote control signals, such as Güralp accelerometers or the CMG-6 series of medium noise instruments. The 4-channel model of the DM24 does not have a SENSOR B port.
On a stand-alone DM24, the digital ports are located on the opposite side to the analogue ports:
DM24mk3-digital-inputs
The DM24 outputs data through its DATA OUT port. This is a standard RS232 serial link, outputting data in GCF format according to the particular configuration of the instrument. The DM24 has a default baud rate of 38,400. You can change this later using the BAUD command or from Güralp Systems' control, acquisition and monitoring software package, Scream! (see chapter 4).
A GPS connector is also provided on the front panel for attaching to a GPS receiver. GPS signals are sent to both digitizers simultaneously, but only the one to which it is directly attached can control the GPS system.
The DATA IN port can be used to access the digitizer's console over a direct serial link, or for inputting additional data streams for transmission in GCF format.
Finally, the DM24 can be supplied with an optional USB client interface for connecting to a PC. When this is present, the USB port acts as a direct replacement for the DATA OUT or console port, and appears as an additional serial port to your computer. You can configure which port is replaced from the digitizer console (see chapter 5).
The optional IEEE.1394 (“FireWire”) ports on the DM24 may be used to download data onto a compatible hard disk. The unit can be supplied either with standard FireWire connectors or with robust mil-spec plugs (see Section 8.5, page 117, for pinout details).
DM24mk3-inside
Before you can use the disk, you will need to reset it. The DM24 saves data on the hard disk in a special format, so you cannot use your PC's operating system to reset the disk.
You can use the DM24 itself, Scream!, or gcfxtract software to reset the disk. For instructions on using Scream! and gcfxtract, please see the documentation for these software packages, or their on-line help.
To reset a FireWire disk with the DM24:
Power up the DM24, and connect it to your computer's serial port.
Open its terminal console. To do this using Güralp Systems' Scream! software, right-click on the digitizer's icon (once it appears) and select Terminal.... From a Güralp DCM, issue the command minicom -n port-number.
Issue the command DISKMENU. You will see the message
Plug in FireWire cable
Plug in your disk. The DM24 will output (on the console) information about the disk as soon as it is detected.
Within the next 7 seconds, press any key to bring up the disk menu.
Press R to reset the disk.
When the reset is complete, remove the disk.
You will now be able to download data onto the disk when required.
When the DM24 is ordered in borehole form, it is supplied with a surface interface unit for installation at the top of the borehole. This unit takes the single data cable from the downhole digitizer and provides standard connections for other equipment.
DM24BH-surface-control-unit-corner
The connectors provided are:
a SENSOR connector - a 10-way mil-spec socket carrying serial data, GPS and power to the sensor;
a GPS connector for attaching to your GPS receiver; and
a POWER / HOLELOCK connector which can either be connected to a source of 12 – 30 V power for supplying to the borehole instrumentation (including sensors), or to a Holelock Control Unit for driving the sensor's hole lock motors. It is not usual to power the sensor and hole lock simultaneously; once the hole lock is engaged, you should remove the Holelock Control Unit and cabling so that the sensor cannot be removed.
On the reverse side, a standard 9-pin RS232 connector is provided for connecting to a PC running Scream! using a straight-through serial cable.
There is also a three-pin mains (outlet) plug, which can power the downhole instrumentation from 110 – 250 V AC as required.