Guralp Systems Limited


1. Introduction 2. First encounters 3. Installing in a borehole 4. Calibrating the 3V / 3ESPV 5. Inside the 3V / 3ESPV 6. Connector pinouts 7. Specifications 8. Revision history

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

Chapter 2. First encounters

2.1 Unpacking and packing

The 3V and 3ESPV seismometers are 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 instrument and should be reused whenever you need to transport it. Please note any damage to the packaging when you receive the equipment, and unpack on a clean surface. The package should contain:

2.2 Handling notes

The 3V and 3ESPV are sensitive instruments, and is easily damaged if mishandled. It 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 instrument

The instrument is delivered in separate sections, which need to be assembled before it 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 Control units

The 3V and 3ESPV are operated from the surface through various control units. All the instrument 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.

For deep-borehole installations (over 50 m) we recommend that you use a breakout box with internal line drivers, to ensure that logic signals are reliably transmitted to the sensor. Contact Güralp Systems for advice.

Note: The breakout box looks very similar to other Güralp breakout boxes. However, its internal wiring is different from that used for some other instruments. For this reason, if you are using several instrument types, you should mark each breakout box clearly so that it is always used with the correct instrument.

Surface control units

Most newer 3V and 3ESPV units have state-of-health (SOH) electronics installed within the sensor housing, which manage the instrument's mass control functions. In some installations, however, these electronics are installed at the surface, in a dedicated control unit. This unit provides the same connectors as the breakout box, but is rather larger. In addition to the SOH electronics, it contains a differential input to differential output amplifier, and a fuse to protect the internal DC–DC converter against polarity reversal. Its connectors are the same as those on the breakout box, except that

The surface control unit is supplied with a 3 m cable as standard. This can be extended up to 100 m without compromising signal quality. The sensor uses amplifiers with high common mode rejection to ensure the signal to noise ratio is maintained over this distance. Individually shielded twisted-pair cabling must be used for the sensor outputs, control lines and power supply. If you need to make up a suitable cable, you should confirm the cable type with Güralp Systems.

The push-button switches which operate the sensor's control commands (mass locking, unlocking, and centring) are housed beneath waterproof lids. You must release the fixing screws holding the lids down before you can initiate any commands.



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.

Mass locking and unlocking

The instrument is delivered with its sensor mass locked, so that they will not be damaged in transit. You should lock the mass whenever you need to move the instrument.

To unlock the instrument, hold down the ENABLE and UNLOCK buttons (or the UNLOCK switch on a surface control unit) for at least six seconds. The sensor's microcontroller will free the mass and ready it for use. Once this is done, the controller automatically starts a centring cycle. If you issue an UNLOCK command when the mass is already free, the instrument will attempt to lock the mass first, and then unlock it in sequence as normal.

To lock the instrument, hold down the ENABLE and LOCK buttons (or the LOCK switch) for at least six seconds. The sensor's microcontroller will lock the vertical sensor mass. The instrument is now protected against accelerations up to 10g, and is ready for transportation.


To centre the instrument, hold down ENABLE and CENTRE buttons (or the CENTRE switch) for at least six seconds. If the masses are locked, the microcontroller will do nothing. Otherwise, it attempts to zero the output of the sensor. Inside, a motor-driven adjuster presses a small spring lever against the boom until the mass position output indicates an offset close to zero.

After successful centring, the mass position outputs should be in the range 0.1 – 0.8 V. If the centring process leaves the mass position outputs above ±1.1 V, start another centring cycle. You will probably need to perform several rounds of centring before the masses are ready.

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.


The HCU provides

Signal meter

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

Calibration and control

You can calibrate a 3V or 3ESPV sensor through the HCU by connecting a signal generator across the yellow and green CALIBRATION SIGNAL inputs and turning the CAL ENABLE dial to V. The sensor's response can now be monitored or recorded, and calibration calculations carried out.

The section of the HCU below the calibration lines controls the instrument's mass control system. To initiate locking, unlocking, or centring, hold down the ENABLE switch on the HCU together with the appropriate switch for the command you want to issue for at least six seconds.

Banana sockets

The remainder of the HCU provides useful 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. You should check the inclination of the instrument before unlocking the sensor masses, since too great a tilt can damage the components.

To measure the attitude of a 3V or 3ESPV 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.

2.5 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. First encounters 3. Installing in a borehole 4. Calibrating the 3V / 3ESPV 5. Inside the 3V / 3ESPV 6. Connector pinouts 7. Specifications 8. Revision history