Chapter 3. Setting up the CMG-6TC

3.1 Introduction

The CMG-6TC is delivered in a single transportation case. The packaging is specifically designed and should be reused whenever you need to transport the instrument.

Note any damage to the packaging when you receive the equipment and then unpack, ensuring the following are present:

• The seismometer;

• The thermal insulation jacket;

• The calibration and installation sheet.

• The connection cable (which contains a DC-DC power converter); and

• The attachable North/South alignment tool, if ordered

The instrument is factory set to the customer-specified response mode. To change the response mode before deployment, carry out the procedure detailed in section 4.

3.2 Handling notes

• Avoid bumping or jolting the instrument when handling or unpacking.

• Do not kink or walk on the cables (especially on rough surfaces such as gravel) or allow any cable to bear the weight of the instrument.

• Do not connect the instrument to power sources, except where instructed.

• Do not ground any of the signal lines from the sensors.

3.3 Deployment

• Stand the instrument on bedrock where possible or, at least, deep in well-compacted subsoil. Remove all loose material from the mounting surface as this will ensure good contact between the instrument and the surface.

• Align the instrument along the North/South axis using the indicators engraved on the top cover or the optional alignment tool (an extended pointer which locates into the two recesses in the top cover).

• For best results, level the instrument using the adjustable feet and bubble level. The instrument can stand unsupported and function on a surface tilted by up to 10°. If buried, the instrument will still function with a tilt of up to 20° but the quality of the output signals will be compromised.

• Lock the adjustable feet in position using the knurled brass locking nuts. The feet are locked when the knurled nuts are tight against the base of the instrument.

• Install the thermal jacket to protect against temperature fluctuations.

• Referring to the instrument pin-outs in Appendix A on page 13:

  • Connect the instrument to suitable digitiser, such as a CMG-CD24 or CMG-DM24.

  • Connect the instrument to a 9-36 VDC power supply.

• Allow a few seconds for the instrument's processor to boot

• The instrument is now operational and transmitting data.

• Allow 4 minutes for the instrument to auto-centre.

  Note: Güralp systems can supply breakout boxes, cables, digitisers and software for data conversion and analysis.

  Note: If you are using a Güralp Systems digitiser, refer to the digitiser manual for details on how to set up the digitiser to receive data.

• If installed in a hole, the instrument can be sealed in a plastic bag (to keep it clean) prior to infilling.

• After installation, the instrument and mounting surface will slowly adjust to the local temperature, and settle in their positions. This typically takes around four hours from the time installation is completed.

3.4 Re-centring

The CMG-6TC automatically centres its masses at power up and should not normally require re-centring. If however, the sensor's position changes due to earth movement or if the ambient temperature changes dramatically, re-centring can be triggered by connecting pin U to pin Y:

• If pin U is connected to pin Y for between one and five seconds, the processor will switch temporarily to one-second response mode and check the mass positions. If they average more than 25% of full-scale, automatic re-centring is initiated.

• If pin U is connected to pin Y for between five and ten seconds, the processor will check the mass positions in the currently selected response mode and initiate automatic re-centring if they average more than 25% of full-scale.