OPERATIONS AND INSTALLATION MANUAL
MODEL S102 SEISMOMETER
Engineering Acoustics, Inc.
933 Lewis Dr., Suite C
Winter Park, FL 32789
1. UNPACKING AND INSPECTION
1a. Unpacking
The Model S102 Seismometer with external power supply, interface cable and hex key wrench
are packaged together in the shipping box. Open the box and note how the instrument
components have been packed. We recommend that this packing arrangement be duplicated
whenever the instrument is transported.
1b. Inspection and Identification of Key Parts
REFER TO DRAWING 160X0005 FOR IDENTIFICATION OF KEY PARTS.
(The letters in the square brackets can be used to locate the part from the drawing)
Remove and inspect the seismometer, power supply and cables. Note that the cable on the power
supply has a 5-pin connector that plugs into the 5-contact power receptacle [A] at one end of the
seismometer. The interface cable has an 8-pin connector that plugs into the 8-contact signal
receptacle [B] next to the power receptacle. These connectors will be mated to their respective
receptacles during the installation.
Identify the locking nut [C1] and black knurled nut [C2] on each leveling screw at the base of the
unit. During installation the seismometer will be leveled using these screws which will then be
locked in place. Also, note the bubble level [D] located on the top rail that indicates whether the
seismometer is level.
Locate the three white nylon transit screws [E1] and locking nut [E2] on the ends of the
seismometer. During shipping, these screws are tightened to lift the pivot off the bearings [G] and
secure the position of the reference mass [H]. These screws will be backed off during installation.
Identify the small spring tension adjustment screw [J] near the top of one end bulkhead. During
installation, this is adjusted (using the hex key wrench provided) to set the equilibrium position of
the reference mass.
If damage is noted contact the carrier to file a shipping damage report. If necessary, contact
Engineering Acoustics for authorization to return a unit.
2. INSTALLATION AND SET-UP
2a. Suitable Locations for the Seismometer
There are a number of considerations that must be weighed when selecting the site for the
seismometer. The following guidelines will help ensure the most effective operation of the S102
Seismometer:
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Dry indoor location on cement slab of ground floor
Area where the unit can remain in unattended operation for an extended period of time
Thin carpeting or linoleum covered floors are acceptable
At least 50 feet from motor vehicle traffic
Area free of direct air flow from heating/cooling vents
Temperature in the 65 to 80 degree F range
Minimum of 20 feet from doorways, metal cabinets or where people frequently walk
Secure area, free from tampering or movement by untrained personnel
Access to power from grounded power receptacles, supplying 105 to 120 V ac
At least 20 feet away from the computer operating site
In some installations, it will be impossible to avoid air drafts and rapid temperature fluctuations
associated with heating and cooling of the building. It may be necessary in this case to place a
wood or glass enclosure over the seismometer. Two small semicircular cutouts in the enclosure
will be necessary to accommodate the power and signal wires, allowing the enclosure to rest onto
the floor without gaps. Make sure that the walls of the box are not in contact with the instrument.
2b. Installation
Two wrenches and a digital voltmeter are required in addition to the hex key wrench provided:
• A 7/16” open-end wrench for use with the locking nuts on the leveling screws
• A 3/8” open-end wrench for use with the nylon locking nuts on arm locking screws
• A digital voltmeter (DVM) that resolves 0 to 3.00 volts DC with +/- 0.01 V accuracy
Set the seismometer on the floor at the selected operating site. Loosen the 7/16" locking nut on
the leveling screws on the base of the unit. Observe the position of the bubble indicator and
rotate the knurled nuts on the leveling screws until the bubble located in the black ring indicates
that the instrument is level. Tighten the locking nuts on all three leveling screws and check the
bubble level. Repeat the adjustment if necessary until the instrument is level.
Plug the power supply cable into the 5-contact receptacle on the end bulkhead. Plug the interface
cable in the 8-contact receptacle. Uncoil the cable and route the free end to the computer. At the
free end, connect the positive lead of the dc voltmeter to the tinned conductor of the blue wire
and the negative lead to the tinned conductor of the black lead. Set the meter to read dc voltage
and to resolve 0 to 3 volts dc. The meter will be used to read a voltage that is proportional to the
distance between the reference mass and the position sense coil located below the reference mass.
Plug the power supply into a 110 V ac / 60 Hz wall outlet receptacle that accepts three prong
(grounded) plugs. Do not use three-prong to two-prong (cheater) adapters when powering either
the seismometer, data logging recorder or computer operated digitizer. The dc voltmeter should
now read between 1.0 and 2.5 volts.
If the voltage is not present, check that the power is on at the outlet receptacle, the voltmeter
leads are connected to the appropriate conductors and that the connectors are properly mated
to their respective receptacles on the unit. If a problem is experienced at this point, do not
continue with the installation – contact EAI for assistance.
If the meter reading is between 1.0 and 2.5 volts, locate the two nylon transit screws on the end of
the unit that has the connectors. Using a 3/8” end wrench, loosen the locking nuts on the screws
and begin backing the screws out equally, both at the same time. Notice that as the screws are
backed out, the pivot locates into the v-groove bearings. Continue backing the screws out until
they are clear of the pivot bar. At the other end of the instrument, loosen the locking nut and
back the nylon screw until it is free of the circular reference mass. Verify that all three screws are
free of the pivot arm/reference mass assembly. The nylon transit screws should not be removed
from the bulkheads.
Caution!
The seismometer can be damaged if roughly handled with the transit screws backed out.
The dc voltmeter reading usually changes, once the pivot arm is free to find its equilibrium
position. Insert the hex hey in the spring tension adjustment set screw (above the connectors) and
turn the screw clockwise to increase the dc voltage reading or counterclockwise to decrease the
voltage reading. Adjust the screw to obtain a voltage reading between 1.5 and 1.7 V dc. This
completes the installation adjustments. Refer to Section (4d) for monthly adjustment information.
Note that whenever the seismometer is picked up or moved to a new operating site, the transit
screws must be returned to their original locking positions, following the above procedure in
reverse order. Make sure the screw is engaged into the reference mass before bringing the two
screws onto the pivot bar. Once the arm is locked, tighten the locking nuts to secure the
screws.
2c. Connection to Computer/Recorder
The output of the seismometer is usually recorded using a computerized system that employs a dc
analog to digital converter to digitize, store and display the incoming analog time series from the
seismometer. The output can also be viewed on a chart recorder that accepts dc inputs.
Identify the input signal terminals of the digitizer/recorder. If the digitizer has a single-ended
input, connect the black lead the common terminal and the white lead to the positive input
terminal. If a digitizer/recorder with differential input is used, connect the shield to common, the
white lead to the + input and the white with blue stripe lead to the – input. If a chart recorder is
used, set the sensitivity to the 1 V dc scale and center the pen on the paper. Make sure that
unused leads on the interface cable are insulated and not touching other wires or the digitizer
frame.
Observe the displayed signal. Walking near the unit should be indicated as a series of rhythmic
pulses on the display. Note also that walking more than 15 feet away from the seismometer will
produce pulses that are quite low in level and may be obscured by the background noise of the
earth.
2d. Interface Cable Color Code
Wire Color
Black
Function
Common
White
White with Blue Stripe
Seismometer output signal
Complement of seismometer
output signal
Displacement signal
Field calibration control
Blue
Blue with White Stripe
Interconnections
Negative lead of DVM and
common terminal of digitizer
Digitizer input
See text
Positive lead of DVM
See text
3. OPERATION
3a. Operation and Observations
When installed and interconnected per the previous section of this manual, the seismometer
should be fully operational.
There are a number of observations and measurements that can be made with the seismometer.
The primary signals observed will be the seismic signals from local and distant (teleseismic)
earthquakes. These signals will comprise compressional (P-waves) which travel at the greatest
velocity through the earth and are usually the first signal observed. Shear (S-waves) travel at a
slower velocity through the earth and arrive after the direct P-wave. The P and S “body” waves
may contain both direct and reflected paths through the earth's interior. The last waves to arrive
are surface conveyed Love and Rayleigh waves. Surface waves travel along a great circle path
from the source to the observer.
The Model S102 Seismometer resolves the vertical component of earth motion all three types of
waves. Travel-time tables are available from texts on seismology. These tables present travel
times for the various wave components as a function of angular distance between the source event
and observer. Using the S-P time interval alone, it may be used to do a preliminary estimate of
distance if these two wave components can be correctly identified.
Information on individual seismic events is available from the USGS via the Internet. Using the
information on the source location, the angular distance from your station to the source can be
calculated using spherical trigonometric relationships. Reference to the travel-time tables will
enable the recorded wave components to be identified as direct or reflected P or S wave
components. This exercise will enable the careful observer to learn the wave appearance for the
various components.
The background vibrational noise of the earth will also be observed, especially during large -scale
storms. These “microseismic” signals have their origin in wind-driven surface waves on oceanic
coastal regions, shallow seas and on the larger inland lakes. Microseismic noise often contains
individual and overlapping wave “packets” that have sinusoidal wave shape, 6 to 9 second period,
build to a maximum amplitude over a few cycles and decrease in amplitude over many cycles.
3b. Some Suggested Internet Site Links
The Internet site and MichSeis Newsletters of the Department of the Geological Sciences at the
University of Michigan are an excellent source of information on using data from the
seismometer. The Internet home page address is http://www.geo.lsa.umich.edu/MichSeis. This
site has links to the USGS for recent earthquake activity reports and other sources of earthquake
information. Information on storms at sea is available from the U.S. Navy at
http://www.152.80.202/wam.html.
4. CALIBRATION, CARE AND MAINTENANCE
4a. Calibration
Factory calibration is performed on each S102 seismometer, and consists of direct measurement
of the displacement sensitivity, linearity and overall frequency response. The instrument
sensitivity is well controlled and should be stable over many years of operation.
EAI has included a means by which the user may perform an in-field calibration to verify that the
seismometer is continuing to operate with the original sensitivity. When activated, the field
calibration circuit applies a precision current to the feedback coil to create a small but controlled
displacement of the reference mass. This mechanical displacement is detected and appears at the
output of the seismometer as a transient pulse which decays to within 1% of full scale within
about 90 sec. The blue with white stripe insulated lead in the interface cable is used to activate
this function. There are two means of activating the calibration function. The lead may be driven
with a TTL compatible digital output from the digitizer. The circuit is off for a digital "1"; a
digital "0" activates the calibration function. In either case, the "0" or "1" must be latched
continuously in the selected state. The alternative is to either connect or disconnect the blue with
white stripe wire to the shield wire using a toggle switch. The seismometer reference mass is
displaced while the contacts in the switch are closed and returned to its neutral position as the
contacts are switched open. Two pulses will result, one at the beginning and one at the end of the
calibration control signal. Equal amplitude pulses indicate proper operation of the mechanical
suspension system for the reference mass, free of mechanical stiction and non-linearity.
4b. General Trouble Shooting Procedure
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Check that the power supply and interface cable are properly mated with the appropriate
receptacles and that the power supply is powered.
Verify the three white nylon screws are backed out free of the reference mass and pivot arm
assembly.
Verify the displacement output voltage is in the operational range and make appropriate
spring tension adjustment as necessary.
Make sure that unused leads on the interface cable are insulated and not touching other wires
or the digitizer frame.
If problems persist, it could be a faulty connection to the A/D converter or its mating connector.
The signal level from the seismometer can be read directly on a sensitive DVM. During periods
of no earthquake activity, the output signal is a slowly changing signal in the range from +3 to -3
dc millivolts. If this signal is observed at the digitizer/recorder input, the problem is in the
digitizer, operating software or in the recorder.
4c. Cleaning
When moving or working with the seismometer, return the transit screws to their locked
position and protect the clear exterior tubing from sharp object that may cause scratching.
The exterior of the tubing may be cleaned if required with an anti-static spray that is compatible
with plastics. The spray, commonly available at stores which sell computer related products, may
be applied to a soft cloth which is used to wipe the surface to remove smudges.
Do not use other cleaning materials on the acrylic plastic tube as they may damage the
surface.
4d. Monthly Adjustment
It is good practice to periodically verify that the dc displacement signal has remained within the
operational limits of 1.3 to 1.9 Vdc on a monthly basis. If an offset has occurred, use the hex key
wrench to readjust this setting to 1.5 to 1.7 V dc as described in the installation section (Sec.2b).
4e. Technical Support
For problems that cannot be resolved following instructions in this manual, contact Engineering
Acoustics, Inc as described below, giving a full description of the problem.
Mail Address:
Engineering Acoustics, Inc.
933 Lewis Dr., Suite C
Winter Park, FL 32789
Facsimile:
(407) 645-4910
e-mail:
[email protected]