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How it works
The HS-3 is designed to detect horizontal motion of the Earth’s surface, based on the classic ‘Lehman’ pendulum design. This comprises a 700mm long boom, with a heavy brass weight at one end, swinging about an axis that is close to vertical. The HS-3 uses tungsten carbide roller bearings for the pivots, which ensures negligible friction and pendulum periods of up to 20s.
As the ground and instrument frame move in response to seismic waves, the pendulum tends to remain stationary. Consequently, seismic motion is recorded in terms of movement between the two parts of the electronic sensor - one part that is fixed to the mass (B), the other fixed to the instrument’s frame (A & C).
HS-3 SEISMOMETER
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The HS-3 incorporates a sensitive capacitance displacement sensor of a type normally only found in high-end, professional instruments. Our design is totally digital, meaning that the drift encountered in analogue electronic components is completely eliminated.
As an added feature, the HS-3 incorporates electronic feedback-centering of the beam, continually compensating for slow shifts of the pendulum due to ground tilt. This signal is transmitted along with the seismic motion, allowing records to be made of Earth tides. A temperature sensor is also incorporated.
| Technical Specification | |
| Concept: | Carbon fibre, Lehman pendulum, with tungsten carbide roller pivots. |
| Levelling: | Manual and remote electronic levelling. Bubble & electronic levels. |
| Sensor: | Digital, symmetric, differential capacitance detector. Internally damped. |
| Natural period: | 5-20s set by calibrated thumb screw. |
| Electronics: | Fully integrated. |
| Max. sensitivity: | 1 count = 3nm/s (approx.) |
| Reading rate: | 3/s, 6/s, 12/s and 24/s |
| Gain: | x1, x2, x4, x8, x16, x32 |
| Dynamic range: | 24 bit. |
| Feedback (tilt): | 16 bit. |
| Temperature: | 0.1°C resolution |
| Communications: | RS232 over 5m cable (supplied). |
| Dimensions: | H=346mm, L=780mm, W=520mm. |
Software and Communications
A custom version of the popular AmaSeis data logging program is provided for the charting, recording and analysis of HS-3 seismic data. AmaSeis can also export and import quake event files in standard SAC format for exchange with other enthusiasts around the world.
A set of useful utilities are also included on the CD, together with a free version of the BBC Basic for Windows programming language, plus source code for all the utilities. The key program is Mission Control, used to help level and configure the HS-3. Watch the video to learn more.
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Sample of a BBC Basic program |
Mission Control |
| Open-source utilities provided: | |
| Termite | A simple terminal program |
| Mission Control | Set-up and control program |
| Slogger | A simple data logger |
| Rate Computer | Program to measure HS-3 data rates |
| Microsize | Empirical modelling of microseisms |
| Macrosize | Empirical modelling of earthquake events |
By experimenting with these Basic programs you will discover how easy it is to communicate with the HS-3, receive data and create your own seismic data plots.
The HS-3 is controlled by a simple one-letter command set:
| HS-3 COMMAND SET | |||
| Description | Code | Type | Key |
| Device? | 97 | Byte | a |
| Reading Rate 1 (3Hz) | 98 | Byte | b |
| Reading Rate 2 (6Hz) | 99 | Byte | c |
| Reading Rate 3 (12Hz) | 100 | Byte | d |
| Reading Rate 4 (24Hz) | 101 | Byte | e |
| Gain=1 | 102 | Byte | f |
| Gain=2 | 103 | Byte | g |
| Gain=4 | 104 | Byte | h |
| Gain=8 | 105 | Byte | i |
| Gain=16 | 106 | Byte | j |
| Gain=32 | 107 | Byte | k |
| Output Polarity Normal | 108 | Byte | l |
| Output Polarity Reversed | 109 | Byte | m |
| Levelling Servo to Centre | 110 | Byte | n |
| Levelling Servo up 1 step | 111 | Byte | o |
| Levelling Servo down 1 step | 112 | Byte | p |
| Auto-feedback On | 115 | Byte | s |
| Auto-feedback Off | 116 | Byte | t |
| Velocity Mode | 117 | Byte | u |
| Displacement Mode | 118 | Byte | v |
For example, just type a command in Termite and the HS-3 will respond! From there, you’ll soon discover that BBC Basic programming is easy and fun.
