151 Observer
from RefTek - A Trimble Band

The 151 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, flat to velocity. The “Observer” with frequency bandwidth 0.033 Hz (30 sec) - 50 Hz is available upon request. The 151 “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.

151B with carry handle. Image courtesy of RefTek, a Trimble Brand.
151B with carry handle. Image courtesy of RefTek, a Trimble Brand.

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

The 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 Observer is a low noise seismometer. The low self noise performance makes the 151-120 an ideal seismometer for local, regional, and global seismicity studies in different installation configurations, including observatory and portable, surface and posthole applications.

Product Dimensions

Physical Dimensions (L x W x H) Weight
151 Observer (instrument only) 24cm x 24cm x 27cm 12kg

Technical Specifications

Sensor Type: Triaxial, Orthogonal.
Feedback: Force-balance with Capacitive Displacement Transducer.
Frequency Bandwidth: 151B-120 0.0083 Hz (120 sec.) – 50 Hz.
151B-60 0.0166 Hz (60 sec.) – 50 Hz.
Sensitivity: 2000 V/m/s.
Full Scale Output: ±20 V Peak-to-Peak Differential.
Dynamic Range: >140 dB @ 5 Hz
Self-Noise: Below NLNM from 145 sec. to 10Hz.
Output Impedance: <100 Ohms.
Calibration: Coil Resistance 1,000 Ω Sensitivity: 10 m/s²/A.
Distortion: Total Distortion <-80 dB.
Cross Axis Coupling: <1%.
Low Spurious Resonance: Higher than 100 Hz.
Damping: 0.7 of Critical.
Linearity: Better than 1% of full scale.
Alignment: Removable orientation N/S pins screw into the base (brass for N, silver for S).
Leveling: Two Integrated Bubble Levels; three adjustable levelling feet with locknuts.
Mass Position: Remote Monitoring and Adjusting Zero-point using 3 Independent Voltage Outputs.
Mass Locking: Mechnical Lock/Unlock Mechanism Accessible on Outside of the Case.
Mechnical Zero: No need for Adjustment within Ambient Temperature Fluctuation ±20°C.
Power Input: +12 VDC (9V to 18 VDC).
Power Consumption: ~1.1 W.
Auto-Recovery Time: Full operation recovery within 10 minutes after either power fail or signal overload.
Operating Temperature: -20° to +60°C.

Data Sheet