Guralp Systems Strong Motion User Manual

Strong Motion
User Guide

User guide

Part No. MAN-SMO-0001

Designed and manufactured by
Güralp Systems Limited
3 Midas House, Calleva Park
Aldermaston RG7 8EA
England

Proprietary Notice: The information in this
manual is proprietary to Güralp Systems Limited
and may not be copied or distributed outside the
approved recipient's organisation without the
approval of Güralp Systems Limited. Güralp
Systems Limited shall not be liable for technical
or editorial errors or omissions made herein, nor
for incidental or consequential damages resulting
from the furnishing, performance, or usage of this
material.

Issue F 2008-07-18

Strong Motion User Guide

Table of Contents

1 Introduction...........................................................................3

1.1 Firmware changes..............................................................................3

2 Digitiser Configuration............................................................5

2.1 Update firmware, upload infoblocks...................................................5

2.2 System identity..................................................................................5

2.3 Basic setup.........................................................................................6

2.4 Enable strong motion mode...............................................................7

2.5 Common scenarios.............................................................................8

3 Viewing Results....................................................................10

3.1 The Unified Status Packet................................................................10

3.2 The Strong Motion Packet................................................................11

3.3 Viewing Packets...............................................................................11

3.4 CMG-STA-DISP Display Unit..............................................................12

4 Calculation Details................................................................13

4.1 Low Latency Waveform Data...........................................................13

4.2 Types of Strong Motion Result..........................................................15

5 Revision history....................................................................17

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1 Introduction

The CMG-DM24mk3 digitiser is capable of performing several
calculations useful for strong motion study. This document
details the setup and operation of the strong motion mode.

The strong motion results are computed and transmitted in
real-time, in parallel with waveform data.

IMPORTANT: Users of the CMG-DM24mk3 machine may be
familiar with the Guralp Systems software package “Scream”.
This software is currently not compatible with strong motion
mode. Scream's configuration dialog must not be used to
configure the digitiser once strong motion mode is enabled,
and it cannot be used to view strong motion data. However,
Scream can still be used to examine the raw data waveforms,
and to open terminal mode on the digitiser.

To follow the instructions in this document, it will be useful to
examine these documents as well:

● Information blocks (each digitiser and instrument pair

must have an information block containing the calibration
values, allowing the strong motion results to be
calculated in ground units):

http://www.guralp.com/articles/20060315-howto­information-blocks/support

● The DM24 manual (and in particular the section on

commandline): http://www.guralp.com/products/DM24/

1.1 Firmware changes

v.103 build 68

This build causes unified status packets (enabled with
+monitor) to revert to deprecated CD status packets. Unified
status packets are required for operation with the CMG-DCM
and must be re-enabled after the upgrade with the
“uspmonitor” command.

v.103 build 70

This build causes the 20sps low latency data output to be
turned off by default (it is still computed for the strong motion
calculations, but not transmitted). To re-enable the data, issue

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Strong Motion User Guide

the “LLstreams enable” command. The data may be turned off
at any time with “LLstreams disable”.

This build also fixes several bugs connected with strong
motion:

● Sometimes, only half of the low latency data was output

(e.g. there would be data for 00:00:00, 00:00:02,
00:00:04 but not for 00:00:01, 00:00:03 etc.). This was
triggered by a GPS sync occuring while the DM24 was
creating such a block.

● Sometimes, there were 21 data samples transmitted in a

low latency block. This was another manifestation of the
GPS sync occuring while creating the block.

● The first SM packet was computed using incorrect values

as the infoblock had not been interpreted yet.

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2 Digitiser Configuration

Below is a set of commands, including sample output, that
should be used to set up the DM24. Commands that should be
typed are emphasised.

Bring up terminal mode on the digitiser. This can either be
done with Scream or with the data-terminal command on a
CMG-DCM or CMG-NAM. You should be presented with a
message similar to the following. Hitting <enter> a couple of
times will ensure the session is responsive.

LW A80800 CMG-3T Command Mode
0 blocks in buffer | 256 blocks free
Guralp Systems Ltd - DM+FW v.103 mgs 17/10/07 (Build 60)
ok_A808

2.1 Update firmware, upload infoblocks

Ensure that the firmware on the CMG-DM24 is up to date. At
the time of writing, the latest versions are Bootloader 1030,
DSP 1060, and system 1.03b70. Later versions will be
backwards compatible. You can follow the instructions at:

http://www.guralp.com/articles/20060914-firmware­DM24mk3/support

Also upload an info block (or two blocks if you have a two­instrument digitiser). Instructions are at:

http://www.guralp.com/articles/20060315-howto-information­blocks/support

2.2 System identity

Now, set the system identity. This gives the System and
Stream IDs of the generated GCF data.

resetlabels ok_A808
set-id

System Identifier { LW } ? 5 characters : LW
Serial # { A80800 } ? 6 characters : A808
LW A80800 CMG-3T ok_A808

If you have a 2-instrument CMG-DM24, you should enable a
second serial number for the second instrument. This is
required otherwise the 2nd info block will not be emitted by the
digitiser. This is achieved with the “serial2” command.

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Strong Motion User Guide

serial2

Secondary Serial # { 0 } ? 6 characters : B808 B80800 ok_A808

GSL recommend that the system identifier is set to the digitiser
serial number, and that the stream identifier is set to the last
four digits of the sensor serial number.

2.3 Basic setup

These steps should be followed to ensure the digitiser behaves
as expected:

6 sensor-type

Sensor type set to CMG-5TD ok_A808

adaptive

Adaptive Storage : Circular ok_A808

erasefile

Are you SURE you want to delete ALL Flash Data? Y/Ny
Erasing ALL 65.5MB
\ 49.1MB
64MB Flash Memory Buffer : 0 Blocks Written 0 Unread 65,536
Free
Oldest data [16] Blank
Read point [16] Blank
Latest data [16] Blank
File Replay [16] Blank ok_A808

normal compression Optimum Compression ok_A808
0 1 bandpass 10.0->90.0HzBandPass ok_A808
3 highpass

HighPass at 1000 sec ok_A808

“6 sensor-type” tells the digitiser that it is connected to a
CMG-5T. This does not alter data acquisition, or the behaviour
of the system, but merely disables some commands, such as
mass lock/unlock, which are not used with strong motion
instruments. The sensor-type command applies only to Sensor
A. Use the command “explain sensor-type” to get a list of
additional sensors.

“adaptive” turns on adaptive mode, in which the digitiser's
internal flash is used as a temporary buffer should data not be
acquired by a connected system. Other digitiser modes such as
FIFO or Direct are also compatible. Consult the DM24 manual to
determine which mode is the most appropriate for you. When
switching into this mode, the command “erasefile” is used to
clean the flash memory, which may contain stale data.

The “compression” and “bandpass” commands are required for
correct operation of lowlatency mode. The “highpass”
command introduces a highpass filter at 1000s, which has the
effect of removing DC offset from the sensor's output. This

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