Guralp Systems Limited


1. Introduction 2. Assembling the instrument 3. Installing the 40TB in a borehole 4. Calibrating the 40TB 5. Connector pinouts 6. Connector pinouts 7. Specifications 8. Revision history

Section Index: 2.1. Unpacking and packing 2.2. Handling notes 2.3. Assembling the 40TB 2.4. Disassembling the instrument 2.5. Control units 2.6. Operating the hole lock

Chapter 2. Assembling the instrument

2.1 Unpacking and packing

The 40TB seismometer is delivered in a single transportation case, with the sensor system and hole lock mechanism (if ordered) packed separately. The packaging is specifically designed for the 40TB and should be reused whenever you need to transport the sensor. Please note any damage to the packaging when you receive the equipment, and unpack on a clean surface.

The package should contain:

The sensor is securely packed, and you will need to remove most of the foam packing before it can be removed.


2.2 Handling notes

The 40TB is a sensitive instrument, and is easily damaged if mishandled. It will not stand vertically upwards without support, and should not be operated until it has been securely installed in a borehole casing. If you are at all unsure about the handling or installation of the device, you should contact Güralp Systems for assistance.

2.3 Assembling the 40TB

The 40TB is delivered in separate sections, which need to be assembled before the instrument can be installed in a borehole. It is recommended that you perform these steps with the help of at least one other person.

Important: Make sure your environment is clean and dust free before assembling the unit. Stray fibres or particles cause damage to the “O”-ring seals between the components and may render the sensor unusable. Do not remove the protective caps on the ends of each unit until you are ready.

2.4 Disassembling the instrument

When the instrument is recovered, you may want to disassemble it. To do this, reverse the steps above, bearing in mind the following points:

2.5 Control units

The 40TB is operated from the surface through various control units. All the 40TB's functions can be accessed through one or other unit. Most can be removed from the site once the instrument is ready for use.

Some of these control units are optional and may not have been supplied with your installation. Their functions can be duplicated either by applying voltages directly to control lines (see appendixes for pinout information) or through a connected Güralp digitizer such as the CMG-DM24. The DM24 digitizer is able to pass commands to the instrument from a Data Communications Module (DCM) or a computer running Güralp Systems' Scream! software, allowing you to access all of the instrument's functions remotely.

The breakout box

The breakout box is normally placed where the signal cable emerges from the borehole. It provides connectors for attaching the various other control units, supplies power to the instrument and relays output signals to a recorder or digitizer.


To calibrate the instrument, the Calibration enable line must be activated. This operates a relay which allows a calibration signal to flow through the transducer feedback coil. This provides an extra force acting on the sensor masses, producing a corresponding deflection in the output signal, which can be analysed by a control computer to extract the seismometer's response characteristics.

Most Güralp instruments are manufactured with active-low Calibration enable lines. However, instruments with active-high calibration can be manufactured on request.

The handheld control unit

This portable control unit provides easy access to the seismometer's control commands, as well as displaying the output velocity and mass position (i.e. acceleration) on an analogue meter.

Signal meter

The upper section of the HCU contains a simple voltmeter for monitoring various signals from the instrument.


You can calibrate a 40T sensor through the HCU by connecting a signal generator across the yellow and green CALIBRATION SIGNAL inputs and setting the adjacent switch to ON. The sensor's response can now be monitored or recorded, and calibration calculations carried out. See Chapter 4, page 22, for full details.

Remote null option

If you have ordered a 40T with the remote null facility, you can zero its mass position offsets from the HCU.

Banana plugs

The remainder of the HCU provides connections for each of the signal lines from the instrument, for attaching to your own equipment as necessary.

The inclinometer monitor unit

The borehole sensor system can operate successfully in boreholes with a tilt angle up to 3.5 °. To check that the instrument is installed suitably close to the vertical, a two-axis inclinometer is installed within the sensor housing. The inclinometer monitor unit is used as a visual guide to the sensor's tilt only, and should not be used if precise attitude information is required.

To measure the attitude of a 40TB instrument:

If you need to use the outputs of the inclinometer for some other purpose, you can also connect a multimeter to the banana sockets on the inclinometer monitor unit.

2.6 Operating the hole lock

The hole lock, if fitted, can be extended and retracted using the hole lock control unit:

Caution: The hole lock may be using high-voltage mains (outlet) power.

Engaging the hole lock

To extend the jaw of the hole lock:

Disengaging the hole lock

To retract the jaw of the hole lock:

Manual operation

If you prefer, you can operate the hole lock by applying voltages directly to the sensor.


1. Introduction 2. Assembling the instrument 3. Installing the 40TB in a borehole 4. Calibrating the 40TB 5. Connector pinouts 6. Connector pinouts 7. Specifications 8. Revision history