Guralp Systems Limited
MAN-050-0005 - CMG-5TD - Operator's Guide

PreviousNext

1. Preliminary Notes 2. Introduction 3. Quick start 4. Setting the gain 5. Operation 6. Calibration 7. Connector pin-outs 8. Specifications 9. Revision History

Section Index: 4.1. Disassembly 4.2. Jumper configuration for low gain operation 4.3. Jumper configuration for high gain operation 4.4. Reassembly

Chapter 4. Setting the gain

The built in 5T sensor has a very large dynamic range. In order to exploit the whole of this range, two separate outputs are available, one with high gain and one with low gain. Normally, the high gain outputs are set to output a signal 10 times stronger than that from the low gain outputs. Only one set of outputs – low gain or high gain – is sent to the digitiser; the selection of which output to digitise is made using internal jumpers.

Note: To change the gain, it is necessary to open the instrument. This work must be carried out in a clean environment in order to prevent contamination of the mechanical components by air-borne dust.

Caution: The CMG-5TD include components which can be damaged by electrostatic discharge (ESD). Always work on a properly grounded dissipative surface and wear a suitable grounded wristband. Ground yourself by touching an earthed conductor before handling any of the circuit boards.

4.1 Disassembly

In order to change the gain-setting jumpers, remove the instrument's lid as follows:

Looking down into the body of the instrument, you will see a small printed circuit board mounted on an aluminium disc. This board contains the gain-setting jumpers, which are coloured red to aid identification.

Each component (vertical, North/South and East/West) has two associated jumpers (one for each leg of the differential connection) and these must always be moved in pairs. It is possible to select different gains for different channels but this is rarely desirable. Consult the markings on the printed circuit board and the pictures below to select the desired gain.

4.2 Jumper configuration for low gain operation

Arrange the jumpers as in the picture below:

4.3 Jumper configuration for high gain operation

Arrange the jumpers as in the picture below:

4.4 Reassembly

Once the desired gain selection has been made, reconnect the ribbon cable and gently lower the lid onto the instrument, taking care not to knock the electronic assemblies or snag any cables. Ensure that the lid is rotated to the correct orientation using the marks you made previously and then gently ease it over the 'O'-ring seal and into place. Secure using the six small screws and, finally, replace the large pressure release screw.

PreviousNext

1. Preliminary Notes 2. Introduction 3. Quick start 4. Setting the gain 5. Operation 6. Calibration 7. Connector pin-outs 8. Specifications 9. Revision History