Chapter 3. Assembling the instrument
3.1 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 seismometer, in sections;
a cable to join the sensor to the breakout box;
the breakout box;
the hole-lock control unit;
a cable strain relief mechanism;
a Hand-held Control Unit (HCU) for monitoring sensor outputs and calibration, if ordered;
a calibration data sheet;
this manual.
The sensor is securely packed, and you will need to remove most of the foam packing before it can be removed.
3.2 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.
Do not bump or jolt any part of the sensor when handling or unpacking.
Keep the sonde sections vertical wherever possible. Carry them by hand and store in a safe rack. Never drag or roll the sonde.
When the sensor is vertical, keep it securely tied down. If the sensor system topples over, you must inform Güralp Systems.
Keep all the parts of the sensor system protected and clean so that they can be joined together securely. Store in the original packaging if possible.
Do not kink or walk on the data cable (especially on rough surfaces such as gravel), nor allow it to bear the weight of the sensor.
Do not connect the instrument to power sources except where instructed.
3.3 Assembling the 40TB
The 40TB is delivered separated from the hole-lock unit, so needs 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.
Caution: 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.
Ensure that the “O”-ring seals on the hole-lock and sensor sections are clean and well greased.
Stand the hole-lock module on the ground with the packing cap at the top. Support it to prevent it from falling over. This can be done either by using an assistant to hold the casing steady, or by strapping it to a support such as a bench leg.
Remove the packing caps from the top of the hole-lock and the bottom of the sensor unit. Beneath the caps are connectors for the hole-lock wiring.
Hold the sensor above the hole-lock unit and join the connectors. Ensure that the connector is fully pressed together and correctly aligned. The wires are fairly short, so you will need a second person to hold the instrument whilst you connect them. Take care not to scratch the other components when attaching the connectors.Align the hole-lock unit with the NORTH mark on the sensor housing. Doing this will allow you to check the approximate orientation of the sensors at a glance.
Push the sensor unit into the hole-lock housing, twisting to align the holes.
Fit twelve M3×8 cap screws into the holes in the joint flange.
When all twelve screws are fitted, begin to tighten them with a ball-ended Allen screwdriver. Tighten evenly, working round the instrument in several passes, until the two sections are securely joined together.
If you are using a single-jaw hole-lock unit, attach skids or studs to the sonde as appropriate for your installation, using the fastenings provided.
3.4 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:
Make sure you only undo the screws that are necessary to disassemble the instrument, and not the ones which hold each module together. Each joint has several sets of screws holding it together. Only one set from each joint needs to be undone—the set which was added during assembly.
When you detach the sensor from the hole-lock module, do not yank them apart, since doing this will damage the connectors inside. Insert flat-head screwdrivers either side of the seal, and carefully lever both sides up simultaneously so that the modules remain parallel. You will need someone to support the upper module as you do this.
When the two parts are separated, tilt the upper one to gain access to the connectors, and disconnect them without scratching the other components.
3.5 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 pin-out information) or through a connected Güralp digitizer such as the GüralpDM24. 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.
3.5.1 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.
The SENSOR connector is a 32-way military-specification bayonet plug, and should be connected to the borehole instrument with the cable provided.
The RECORDER connector is a 26-way military-specification bayonet plug. This should be connected to an analogue data recorder or stand-alone digitizer. In systems using down-hole digitizers, this is replaced by a 10-way military-specification bayonet serial connector for attaching to a Data Communications Module (DCM), modem or other communications link.
The CONTROL connector is a 26-way military-specification bayonet plug intended for connecting to an external controller or Hand-held Control Unit. It has the same pin out as the RECORDER connector.
The POWER connector is a 10-way military-specification bayonet plug, which should be connected to a source of 12 – 30 V DC power, for supplying to the borehole instrumentation. When operating the hole-lock, you should remove the power cable from here and connect the Hole-lock Control Unit to this connector. Because of the high voltages employed, the hole-lock circuitry is entirely isolated from the rest of the electrical systems in the sensor and surface unit; it is not usual to power the sensor whilst using the hole-lock.
3.5.1.1 Calibration
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.
3.5.2 The hand-held 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.
3.5.2.1 Signal meter
The upper section of the HCU contains a simple voltmeter for monitoring various signals from the instrument.
To monitor the signal outputs, switch the dial to V, N/S or E/W LOW VEL according to the component you want to monitor.
To monitor the mass position outputs, switch the dial to V, N/S or E/W MASS POS.
You can set the range of the meter with the RANGE switch. When switched to 10 V, the meter ranges from –10 to + 10 V (as marked.) When switched to 1 V, the range is –1 to +1 V.
3.5.2.2 Calibration
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.
3.5.2.3 Mass controls
To zero any offset of the instrument’s mass positions a centre operation can be remotely triggered by holding down both 'enable' and 'centre' switches simultaneously.
3.5.2.4 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.
3.6 Operating the hole-lock
The hole-lock, if fitted, can be extended and retracted using the hole-lock control unit:
Warning: The hole-lock may be using high-voltage mains (outlet) power.
Connect the hole-lock control unit to the HOLELOCK POWER connector of the breakout box, and to a mains power supply. Alternatively, connect a 12 – 24 V DC power supply across the input terminals of the hole-lock control unit.
Warning: Do not connect both DC and mains power at the same time.
Caution: The hole-lock control unit supplied in regions with 220 V AC mains power differs from that supplied for 110 V AC mains power. You should ensure that you provide the correct voltage to the hole-lock control unit, otherwise damage may result to the sensor.
Power down the sensor. The hole-lock will only function whilst the power is off, to avoid injecting current transients from the mains power supply into the sensor electronics.
If you are using a deep-borehole hole-lock control unit, set the dial to zero.
3.6.1 Engaging the hole-lock
To extend the jaw of the hole-lock:
Hold the switch on the hole-lock control unit in the EXTEND JAW or + position. If you are using a deep-borehole control unit, there will be an additional dial compared to the unit pictured; turn this until the built-in ammeter reads around 0.1 A.
When the arm makes contact with the borehole casing, the current will drop slightly. Continue holding the switch in the EXTEND JAW position.
When the lock arm reaches its fully extended position, the motor will automatically stop and the current will drop to zero. If using a deep-borehole unit, return the dial to zero.
If the current has not dropped quite to zero after 30 – 40 s of operation, release the switch, wait a few seconds, and push it back to the EXTEND JAW position briefly. If the arm is not completely extended, you will see a surge of current. If the current remains constant, the jaw is at its maximum reach.
Once the sensor is locked in place, it is recommended that you remove the hole-lock power cable and control unit from the site. Without power, the hole-lock will not be able to retract, and the sensor will be secure.
3.6.2 Disengaging the hole-lock
To retract the jaw of the hole-lock:
Tension the load bearing cable, to take up any slack.
Hold the switch on the hole-lock control unit in the RETRACT JAW or – position. If using a deep-borehole control unit, also turn the dial until the built-in ammeter indicates 0.3 – 0.5 A. More current is drawn retracting the arm, because the motor is now working against the spring.
When the lock arm reaches its fully retracted position, the motors will automatically stop and the current will drop to zero. If using a deep-borehole unit, return the dial to zero.
3.6.3 Manual operation
If you prefer, you can operate the hole-lock by applying voltages directly to the sensor.
To extend the jaw, connect the Hole-lock Motor pin on the sensor (or on the breakout box's HCU or RECORDER connectors) to a +12 V power source, and the Hole-lock Motor Return pin to 0 V.
To retract the jaw, reverse the polarity so that the Hole-lock Motor Return pin is at +12 V and the Hole-lock Motor pin is at 0 V.