Polarity of output signals
This page describes the polarity of the output signals of Güralp analogue instruments - i.e. whether the output goes positive or negative when the instrument or ground moves in a particular direction. Velocimeters, such as 3, 40 and 6-series instruments, have two sets of outputs: velocity outputs and mass position outputs. Accelerometers, such as 5-series instruments, only have acceleration outputs. These different types of outputs will be treated separately in the following sections.
Velocimeters: velocity outputs
Response to motion
Velocity outputs are canonical with respect to ground motion, so:
- If the ground moves to the North, the North/South output will go positive.
- If the ground moves to the South, the North/South output will go negative.
- If the ground moves to the East, the East/West output will go positive.
- If the ground moves to the West, the East/West output will go negative.
- If the ground moves vertically upwards, the Z output will go positive.
- If the ground moves vertically downwards, the Z output will go negative.
Response to tilt
Velocity outputs are AC-coupled so there will be no permanent response if the instrument is tilted. There will, however, be a response while the instrument is being moved.
Velocimeters: mass position outputs
Response to motion
The mass position outputs of velocimeters respond to the first differential of motion
Response to tilt
- If the instrument tilts so that the top moves to the North, the North/South output will go negative.
- If the instrument tilts so that the top moves to the South, the North/South output will go positive.
- If the instrument tilts so that the top moves to the East, the East/West output will go negative.
- If the instrument tilts so that the top moves to the West, the East/West output will go positive.
- If the instrument tilts so that the top moves vertically upwards, the Z output will go negative.
- If the instrument tilts so that the top moves vertically downwards, the Z output will go positive.