Guralp Systems Limited
MAN-050-0004 - 5T Compact Accelerometer

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1. Preliminary Notes 2. Introduction 3. Installation 4. Calibration 5. Inside the 5T Compact 6. Connector pin-out 7. Specifications 8. Revision history

Section Index: 3.1. Unpacking and packing 3.2. Initial testing 3.3. Installing the sensor 3.4. Removing offsets from the 5T Compact 3.5. The hand-held control unit

Chapter 3. Installation

3.1 Unpacking and packing

The 5T Compact accelerometer is delivered in a single cardboard box with foam rubber lining.

The packaging is specifically designed for the 5T Compact and should be re-used 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:

Place the accelerometer on a clean surface and identify:

If you need to request the sensor production history, you will need to quote either the serial number of the sensor or the works order number, which is also provided on the calibration sheet.

3.2 Initial testing

To test the 5T Compact before installation, you will need a power source which can deliver >100 mA at 10 to 36 V to cover initial transients and a digital voltmeter (DVM) with 1 and 10 V ranges. Also ensure that the supplied cable is connected with the correct polarity.

To make it easier to measure the output from the sensor, you can use a Hand-held Control Unit or an improvised interface box, which can be manufactured from a screw clamp connector block. This will simplify the connections to the appropriate connector pin outputs.

If the performance so far has been as expected, the instrument may be assumed to be in working order and you may proceed to install the unit for trial recording tests. In many cases, there will be a slight offset to the readings. This can be compensated for after installation, by adjusting potentiometers (see Section 3.4).

3.3 Installing the sensor

You will need a hard, clean surface such as a concrete floor, to install the 5T Compact.

If you are in any doubt about how to install the sensor, you should contact Güralp Systems.

3.3.1 Temporary installations

5T Compact sensors are ideal for monitoring vibrations at field sites, owing to their ruggedness, high sensitivity and ease of deployment. Temporary installations will usually be in hand-dug pits or machine-augered holes. Once a level base is made in the floor, the accelerometer can be sited there and covered with a box or bucket. One way to produce a level base is to use a hard-setting liquid:

If you prefer, you can use quicker-setting plaster or polyester mixtures to provide a mounting surface. However, you must take care to prevent the liquid leaking away by “proofing” the hole beforehand. Dental plaster, or similar mixtures, may need reinforcing with sacking or muslin.

3.3.2 Installation in Hazardous environments

The fully enclosed, aluminium case design of the 5T Compact instrument makes it suitable for use in hazardous environments where electrical discharges due to the build up of static charge could lead to the ignition of flammable gasses. To ensure safe operation in these conditions, the metal case of the instrument must be electrically bonded ('earthed') to the structure on which it is mounted, forming a path to safely discharge static charge.

Where electrical bonding ('earthing') is required during the installation of a 5T Compact instrument, the central mounting hole that extends through the instrument should be used as the connection point. This is electrically connected to all other parts of the sensor case. Connection can be made by either a cable from a local earthing point terminated in a 8mm ring tag or by the mounting bolt itself.

3.4 Removing offsets from the 5T Compact

Once installed the sensor needs to be as level as possible to ensure the output offset is minimised. Levelling is carried out by adjusting the feet until the bubble level on the top of the sensor has the bubble completely within the scribed ring.

When power is applied to the 5T Compact, offset adjustments are carried out automatically.

For more information about the effects of offsets and how to avoid them, visit http://www.guralp.com/minimizing-sensor-offsets/.

Should there be a need to reset the offsets, the simplest method is to power cycle the sensor. If this is not possible the following methods can be used.

3.4.1 Manual offset removal

Early versions of the 5T Compact had a port in the sensor lid to allow for manual offset adjustment. If the sensor has a knurled screw cover then there is a manual offset adjustment option.

After the cover is installed, the accelerometer outputs may drift until the system establishes temperature equilibrium with its environment and the sensor settles down in its position. If required, the offset adjustment can be repeated to achieve a better output offset. With experience, it should be possible to reduce the output level to less than ±1 mV.

3.4.2 Removing offsets using a terminal connection

Note: this method will only work for the instrument connected to the sensor A port on a digitiser.

Open a terminal window for the required sensor and enter the command:

CENTRE MONITOR

or

CENTER MONITOR

The current offset values will display. Once the process has completed the Scream! status window will display (in green):

CENTERING COMPLETE

Note: if you enter the command CENTRE or CENTER the process will still take place but the mass position values will not display.

3.4.3 Removing offsets using a third party digitisers

To remove offsets while using third party digitisers, connect pin U on the sensor connector to pin Y (see section 6). Note that the sensor must be powered while performing this operation.

The connection between pins U and Y must be maintained for seven seconds before the centring function is activated. The connection must then be released. Centring will continue for as long as is required after the connection is broken,

3.5 The hand-held control unit

The 5T Compact can be supplied with an optional hand-held control unit (HCU). This is a portable device which provides easy access to the seismometer's controls, as well as displaying the output acceleration on an analogue meter. The 5T Compact uses the same HCU as Güralp 5TB and 40T instruments but there are a few differences. The output from the 5T Compact is acceleration not velocity so, to view the high gain acceleration, select the 'HIGH VEL' switch and to select the low gain acceleration select the 'LOW VEL'. The 5T Compact also doesn't output the mass position and has no electronic centring so these parts of the HCU should be ignored.

3.5.1 Signal meter

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

3.5.2 Calibration

You can calibrate a 5T Compact 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 15, for full details.

When you have finished calibrating, switch the ON/OFF switch back to the OFF position.

3.5.3 Open-loop response

The next section of the HCU contains a dial marked CENTRING SELECT and two switches. The CENTRING SELECT dial and the switch next to it have no effect on 5T Compact instruments: the 1 SEC VEL / BB VEL switch is used to enable open-loop response mode.

To place the instrument in this mode, move the switch to 1 SEC VEL. The feedback loop will be broken, allowing the masses to move freely. To return to normal operation, move the switch back to BB VEL.

3.5.4 Banana sockets

Beneath the CENTRING SELECT dial (which is not applicable to 5T Compact instruments) are connections for each of the signal lines from the instrument, for attaching to your own equipment as necessary.

PreviousNext

1. Preliminary Notes 2. Introduction 3. Installation 4. Calibration 5. Inside the 5T Compact 6. Connector pin-out 7. Specifications 8. Revision history