| Q1: |
Which versions of the sensor are available? |
| A1: |
We offer two different versions: FPS1010 - 1 axis system, FPS3030 - 3 axes system. The specifications for both systems are the same. There are also different options available such as the /SYNC option (see FAQ entry for /SYNC option) and the environmental compensation option (coming soon). |
| Q2: |
What is the /SYNC option? |
| A2: |
The /SYNC option adds an Ethernet interface to the hardware of the sensor which will be delivered in combination with an EPICS driver set. A TCP/IP protocol will be delivered with the /SYNC option as well. |
| Q3: |
Which type of measurements can be performed with the sensor? |
| A3: |
The FPS is based on a Fabry-Perot interferometer and can measure displacements. The current system can be used to measure relative diplacements as opposed to the absolute distance to a certain target. The system can also be used for vibrometry measurements. A vibrometry experiment is an experiment where displacement magnitudes are displayed in frequency space. The transformation from real-time displacement to displacement in frequency space is referred to as “Fourier Transformation” and is calculated in the FPS3010 hardware. The software which is delivered with the system displays the results of the Fourier Transformation. |
| Q4: |
How difficult is the alignment procedure? What is the alignment tolerance of the target? |
| A4: |
The alignment procedure is very easy for the user. During startup of the system the FPS3010/1010 continuously varies the laser temperature and thus the laser wavelength. At the same time, the signal contrast is measured and translated into a "signal strength" indicator. The user only needs to vary the sensor/target angle until maximum signal strength is reached. Alignment tolerances remain +/- 0.4 ° for the standard system/collimator at less or equal 100mm working distance. |
| Q5: |
Will I need a computer to control the Sensor system? |
| A5: |
For the initial alignment procedure the sensor has to be connected to a PC or tablet PC. After that the system is truly stand-alone during measurement. The measurement data can then either be further processed via the real-time outputs A-quad-B and HSSL or stored to a PC via the USB interface. |
| Q6: |
Which interfaces are available for the sensor system? |
| A6: |
The standard interfaces are USB as well as the real-time interfaces AquadB and HSSL. |
| Q7: |
What is the resolution of the AquadB and HSSL interfaces? |
| A7: |
The A-quad-B output has a user adjustable/incremental resolution, i.e. each A-quad-B cycle can represent anything from 25pm to infinity (25pm is the smallest incremental "tick"). When using the A-quad-B output the signal constantly has to be recorded (each “tick”) since otherwise the position information is lost. The A-quad-B values have to be adjusted to values larger than 25pm in case larger continuous displacement velocities shall be monitored. For example, if the target moves at a velocity of 1m/s, the A-quad-B resolution needs to be adjusted to 100nm in order not to lose track of the true position of the sample. The highest resolution of 25pm can only be achieved at a speed of 250 µm/s.
The HSSL output is absolute. Here, the position will be given at a 10MHz clock rate and at any given point of time the position can be recorded. The signal does not have to be tracked constantly as compared to the A-quad-B signal. |
| Q8: |
Is the system delivered with a software? |
| A8: |
Yes, it comes with a daisy software in which position measurements can be displayed. A fourier analysis for vibrometry is also available. The data can be saved via the USB interface on a PC or further processed via the real time interfaces A-quad-B or HSSL. |
| Q9: |
Are software drivers available?
|
| A9: |
Yes, the system is delivered with labview drivers and Epics drivers will be provided in combination with the /SYNC option (see FAQ entry for /SYNC option). |
| Q10: |
What is meant by digital sensitivity? |
| A10: |
The digital sensitivity is the smallest increment the electronics of the sensor system can resolve. |
| Q11: |
What is the repeatability of the system? |
| A11: |
The repeatability is equal to the stability of the system over time (see attached pdf below). The repeatability depends on the stability of the laser wavelength as well as the cavity length. The laser wavelength is stabilized by locking on the absorption frequency of a gas cell which results in a wavelength stability of 5*10-8. The repeatability scales with the cavity length and is specified to 2nm@20mm, 3nm@50mm, 5nm@100mm and 50ppb for any larger cavity length. These values are valid for a bandwidth of 100Hz and vacuum conditions (see FAQ entry for ambient conditions). The measurement below shows an actual repeatability of 250pm@40mm (recorded in vacuum at a bandwidth of 100Hz) – which is better than specified but routinely achieved. |
| Q12: |
What happens when the sensor is used in ambient conditions compared to vacuum conditions? |
| A12: |
All specifications given are measured in vacuum conditions. Variations in pressure, temperature, and humidity will vary the optical index of refraction. Assuming a standard and homogeneous air composition, a one part-per-million error in position detection results from any one of the following conditions:
-
a 1 °C (20F) change in air temperature,
- a 3.5 mbar change in air pressure,
- a 80% change in relative humidity.
A 1ppm position error corresponds to an apparent position variation of 100nm at 100mm length (approx. 90mm working distance for a standard collimator).
Our standard head are double path interferometers meaning that the light travels four times the distance with degraded ambiant conditions between fiber-end and target. |
