Prototype documentation

Functional Prototype of the

Six-degree-of-freedom (6DOF) Seismic Sensor Rotaphone-D

according to patent CZ 301217 B6

Purpose: collocated measurement of three perpendicular ground velocity components (two horizontal and one vertical) and three seismic rotation rate components (around two horizontal axes and one vertical) in a high-frequency range 2-100 Hz

Figure 1: (a) the 6DOF Seismic Sensor Rotaphone-D from above, (b) the 6DOF Seismic Sensor Rotaphone-D - side view, (c) a simplified basic scheme of the instrument.

Short description:

The device consists of 16 geophones (standard sensors widely used in reflection seismology - passive devices which convert seismic vibrations into an electrical signal producing an output voltage which is proportional to the geophone velocity). The geophones are mounted near the edge of a massive metal disc. In field measurements, the disc is put on a metal supporting plate anchored to the ground. The supporting plate allows the disc to turn around the vertical axis by exactly 45°, so that after eight rotation increments the individual geophones turn full circle, which is useful when the seismic source is capable of producing identical source pulses repeatedly (e.g. in prospecting measurements). The disc and the supporting metal plate are attached to each other by means of a central fixing screw. The analog outputs from the individual gephones are converted to digital outputs by a 16-channel A/D transducer attached to the disc. The device contains also a GPS antenna used to synchronize time.

Parameters of the instrument:

frequency range

2–100 Hz

sampling frequency

250 Hz

LSB for translational components

1.51 nm/s

LSB for rotational components

3.77 nrad/s

maximum translation velocity

12.67 mm/s

maximum rotation rate

31.68 mrad/s

translational dynamic range

138 dB

rotational dynamic range

120 dB

paired sensor spacing

40 cm

Dimensions:

disc diameter

44.5 cm

height

11.2 cm/8 cm (without the metal support plate)

Weight:

15.3 kg

Material of the disc and the supporting plate:

AlMg3 according to the Standard EN 573-3

Basic components:

8 horizontal geophones SM-6 HB 4.5 Hz

3500 ohm 1006250 (ION Sensor Nederland b.v.)

8 vertical geophones SM-6 UB 4.5 Hz

3500 ohm 1006245 (ION Sensor Nederland b.v.)

1 A/D converter

24bit (Embedded Electronics & Solutions, Ltd.)

1 GPS receiver and antenna

Garmin GPS 18

1 datalogger

 

Geophone parameters:

natural frequency

4.5 Hz

sensitivity

78.9 Vs/m

open circuit damping

0.58 5%

maximum coil excursion p.p.

4 mm

standard coil resistance

3500 5%

diameter

34 mm

height

65 mm

weight

170 g

moving mass

10 g

operating temperature range

-40 – +100 °C

A/D converter parameters:

bits

24

channels

16

range

2.5 V

Datalogger parameters:

CPU Intel Atom Dual Core N2600,

1.6 GHz

Memory

2GB DDR3

1x HDMI + 1xVGA

 

1x RS232

 

4x USB 2.0

 

LineIn + LineOut (audio)

 

60GB SSD

 

operating temperature range

-20 – +60$^{circ}$C

Power supply adapter

12V

Dimensions

95 x 134 x 44 mm

Software:

DA16 EEAS Monitor (Embedded Electronics & Solutions, Ltd.)

RotaCal (author Jiri Malek)

Year of construction: 2015

Owner: Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic

Inventory No: KG 14472

Figure 2: Drawing of the metal disc with the circumferential segments containing geophone slots (top view).

Figure 3: 3D view of the metal disc with the circumferential segments containing geophone slots.

Figure 4: Detailed drawing of one of the circumferential segments with slots for one vertical and one horizontal geophone.

Figure 5: 3D view of one of the circumferential segments with slots for one vertical and one horizontal geophone.

Figure 6: Drawing of the metal support plate with holes and pre-drilled dimples (top view).

Figure 7: 3D view of the metal support plate with holes and pre-drilled dimples.