Broadband Seismometer "Observer"

Model 151B-120 / 151B-60 / 151B-30


  • High Performance Broadband Seismometer
  • Low Self-Noise Over a Wide Bandwidth
  • Portable Design
  • Low Power Consumption
  • Force-Balance Electronic Feedback
  • Robust Mass Locking Mechanism
  • Easy Installation


  • Local and Regional
  • Broadband Surface or Posthole Installation
  • GSN Installation
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Broadband Seismometer "Observer"

The 151B series Broadband Seismometer, “Observer”, is a force-balance feedback sensor available with frequency bandwidth 0.0083 Hz (120 sec) - 50 Hz, and 0.016 Hz (60 sec) - 50 Hz and 0.033 Hz (30 sec), flat to velocity. The 151B “Observer” contains three independent sensors (one vertical and two horizontal) with built-in electronic feedback circuit, control and power conversion circuits, featuring low noise, large dynamic range and easy installation and use.

The 151B Observer has built-in leveling and mass lock/unlock facilities. The leveling mechanism includes two bubble levels, three adjustable feet and three locknuts which are located on the seismometer’s chassis (see photo below).

The 151B Observer has built-in mass zero-position adjusting mechanism to perform automatic mass adjustment. As soon as the seismometer is powered it checks the zero position of each component’s mass and automatically adjusts the zero position if needed. Monitoring and adjustment of the mass can also be performed via the 130 family High Resolution Recorders using Sensor Control Board, RT527-B01.

The 151B Observer is a low noise seismometer (see below Power Spectral Density plot). The low self noise performance makes the 151B-120 an ideal seismometer for local, regional, and global seismicity studies in different installation configurations, including observatory and portable, surface and posthole applications.

151 Closeup

Noise Model for REF TEK 151B

Power Spectral Density Plot

Sensor Type

Triaxial, orthogonal


Force balance with capacitive displacement transducer

Frequency Response

0.0083 Hz (120 sec) - 50 Hz (see diagram in manual), Model 151-120
0.0166 Hz (60 sec) - 50 Hz, Model 151-60
0.033 Hz (30 sec) - 50 Hz, Model 151-30 (optional upon request)


2000 V/m/s

Output Signal

+/- 20 V peak-to-peak differential

Dynamic Range

>140 dB @ 5Hz

Output Impedance

<100 Ohms


Coil resistance 1,000 Ohms, sensitivity: 10 m/s2/A


Two Integrated bubble levels. Three adjustable leveling feet with locknuts

Mass Position

Remote monitoring and adjustable zero-point using 3 independent voltage outputs

Mass Locking

Mechanical lock/unlock on outside of the case


Total distortion less than -80 dB

Cross Axis Coupling

< 1%

Mechanical Zero

No need for adjustment within ambient temperature fluctuation +/- 20o C

Power-Fail Protection


Signal Overload Protection


Auto-recovery Time

Full operation recovery within 10 minutes after either power fail or signal overload

Supply Voltage

9 to 18 VDC

Operating Temperature

-20o C to +60o C

Power Consumption

~ 1.1 W

Water Tight Integrity

IP67 for outdoor use and immersion resistance


Aluminum, Powder Coated


Diameter: 9.45 " (24 cm); Height: 10.6 " (27 cm)


26.4 lbs (12 kg)


PTO2A 14-19S


Removable orientation North(brass) / South(silver) pins screw into the base

Accessories (optional)

Rugged transportable hardigg case. Flexible insulation bag (P/N 151-9800)

151B Standard Observer Kit

The 151B Standard Observer kit includes: a) Seismometer; b) T-type Allen wrench key for leveling; c) Aluminum carrying case with pre-cut foam; d) orientation pins

Standard Observer Kit

151B Optional Ruggedized Transport Case

The 151B Observer is available with an optional ruggedized transportation case and thermal insulation bag.

Thermal Insulation Bag

The 151B Observer's transportation case is a ruggedized, durable, lockable case with handles and removable casters, designed for multiple shipments by any means of transportation in a harsh environment.

The transportation case has pre-cut foam to house the 151B Observer with carrying case, removable casters and accessories, including sensor cable and thermal insulation bag.

The 151B Observer's thermal insulation bag is fabricated from Microfleece material with primaloft insulation, providing protection from wind and daily temperature fluctuations in the vault to insure the highest quality data.

Optional Ruggedized Transport Case

REF TEK equipment consists of four major product lines: