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Frequently asked questions.

Do you have any questions for SIOS customer service? Below is a collection of frequently asked questions and the appropriate answers. If you cannot find what you are looking for here, please use our support form.


He-Ne-lasers are the traditional laser sources for precision interferometry. In interferometry the laser wavelength is the measurement reference. The wavelength of a SIOS He-Ne laser is traceable back to international standards and is calibrated against an Iodine stabilized He-Ne laser. This certified traceability to a national calibration standard is essential in the application of laser interferometry for use as a calibration tool.

Furthermore, the SIOS He-Ne lasers have excelent wavelength stability and are almost completely unaffected ba ageing. At the moment similar traceablility and stability when ageing cannot be achieved with laser diodes. 


Regarding the international laser safety standard DIN EN 60825-1, the SIOS interferometer is classified in the laser safety class 2M. The automatic reflex of the eye to close with exposure to bright light sources provides sufficient protection in this classification so special safety glasses are usually not requiered.

An exception is the laser-interferometric gauging probe of LM-series with laser safety class 1, because the laser radiation does not penetrate to the outside here.

The stand-alone lasers SL02/SL03/SL04 (available without the interferometer and only as a laser light source) have slightly higher power and belong to the laser safety class 3R. Directly looking into thislaser witht the naked eye may be dangerous, so special laser protection glasses for 632nm lasers are required. Other precautions may also be required (mechanical interlocks).

For more information contact your national standard agency.


The light from the He-Ne-laser is fed to the sensor head via a special optical fiber. This has the following main advantages:

  • Due to optical fiber coupling, the laser and controller can be located away from the measured object preventing heat from the laser affecting the object. This also reduces potential sources of vibration affecting the head.
  • The fiber coupled sensor head is much smaller than a laser. The head is therefore much better suited for measurements in limited space and can be easily placed in any orientation.
  • The adjustment of the sensor head is much easier and faster because only two components (fiber coupled sensor head and a reflector) must be aligned, instead of three components (laser, interferometer, reflector).

The sensor head can be constructed from aluminum (standard), stainless steel and invar. For normal calibration applications aluminum is preferred because long term stability (> hours) doesn’t play a key role in most applications. Aluminum is also lightweight, making the sensor easier to mount.

For measurements where long term stability is important or for integration of the sensor head into machine assemblies, the thermal expansion coefficient of the sensor material should match the base material to avoid stresses due to differing mechanical expansion. Sensor heads constructed in stainless steel match steel and granite assemblies. Sensor heads made of invar match Zerodur, ceramics and quartz assemblies. For more details please contact SIOS.

The following interfaces are available:

  • USB, incl. SIOS-software for displacement, angle and vibration measurements
  • RS-232
  • AquadB: digital incremental quadrature signals with a configurable resolution from 1 nm to 10 µm via RS422-level for up to four simultaneous channels. This interface is often used as feedback sensor in position control systems or with motion controllers and other closed loop systems.
  • Analog quadrature signal with 1 Vss amplitude (Heidenhain encoder standard).
  • Parallel digital interface with 36 bits: Outputs the measurement values as a 36 bit digital data word. This interface is used if high data rates are required. A PC digital-I/O card, for instance from National Instruments, is required to interface with this output.
  • Analog displacement signal: The measured displacement (length value) is provided as an analog voltage (0-1V), with several selectable sensivities (Vper nm). This option is often used in vibrometry because traditional vibrometry systems also offer these analog interfaces. For a true length measurement, the analog voltage is normally not sufficient due to its limited resolution.

The USB interface is available in nearly all devices as a standard. The other interfaces may be ordered as optional components.

We offer the following standard software for our interferometers or vibrometers:

  • InfasNTC: Software for displacement or length measurement with graphics, data saving and data export,
  • InfasVibro: Software for vibration measurement, incl. real time, FFT-analysis
  • InfasAXIS: Software for calibrating different types of axes, tooling machines, coordinate measurement machines (CMM) and similar equipment
  • InfasMTCAL: Software for calibrating and correcting different types of axes, tooling machines, coordinate measurement machines (CMM) and similar equipment
  • InfasALIGN: Software for fast axle alignment
  • InfasPOINT: Software for acquisition of single measured values for transfer to a subordinated data base or software
  • InfasGAUGE: Software for the Gauge Block Calibration System EPP

Some tasks require the creation of software for the specific application. We have a large library of standard solutions and extensive experience in measurement applications to fall back on. Feel free to contact us for more details. 

Yes. You can access the USB- and RS232-interfaces. We offer a comprehensive software support:

  • a Win32/Win64 DLL to embed the interferometer in Windows software, incl. a description of the API and example software written in C. The DLL can be used in most of the programming languages available for Windows.
  • a .so library for Linux for most architectures (i386, amd64, armhf …)
  • Examples in LabView
  • Examples for Mathlab and Python

The interferometer controller has trigger inputs to trigger the measurement of single values and to trigger the start of a measurement. It enables the synchronization with other measurement equipment with a common TTL pulse. The trigger has low latency to external events like activations of index switches and incremental encoder pulses.

Optionally a trigger generator card can be installed which can produce a software controlled common trigger pulse for synchronizing different measurement devices. 

Calibrations of SIOS interferometers at the German national institute PTB have shown mean systematic deviations in the range around 0.12 ppm which is equivalent to 120nm/m.

The measurement accuracy of a laser interferometer in air is mainly influenced by the air refraction along the laser beam. To determine the air refraction environmental parameters like temperature, air pressure and humidity are measured with high precision.

In practice the limiting factor is the assembly in which the interferometer is installed. This is because it must guarantee sufficient stability (thermally and vibrationally) and allow representative measurements of the environmental parameters to be measured. Please ask us for more support.

Independent of the measurment accuracy the signal processing resolution is around 5 pm. This resolution is particularly noticeable in ultra-stable assemblies, for example in a vacuum or with vibrometry. 

Yes. Traceable measurements are essential for calibration applications and our interferometers are developed with the prerequisite to facilitate traceable measurements.

The calibration of our laser interferometers is the responsibility of national standards institutes. A list of related offers can be found on the website of the BIPM. In Germany the PTB in Braunschweig makes these calibrations for SIOS.

As an alternative to a calibration of the whole interferometer at a national institute, SIOS can provide separate test reports or DAKKS calibrations for laser frequency and environmental sensors (temperature, air pressure, humidity).


SIOS has extensive experiences with measurements in vacuum. Implementing a sensor head in vacuum requires special materials for sensor head, cables, connectors and vacuum feed throughs. Vacuum compatible systems are available on request. When requesting a vacuum compatible system please specify your application and the specification of the vacuum in mbar. 


Maintenance should be carried out after each maintenance period by trained specialists from SIOS. We recommend a maintenance interval of one year depending on the application. For regular maintenance, we recommend starting a maintenance contract.


Need help as soon as possible? Please use our contact form for support requests.

You are welcome to send us your support requests directly to

Please ensure to send us necessary information such as name, address, serial number of the system or a photo with your support request. You don't need an RMA number to send your device to us. As soon as we recieve the system the RMA number will be automatically assigned and shared with you. After a thourough examination of the product, you will immidiatly recieve a non-binding repair offer. 

We answer inquiries on loaner units as quickly as possible via our sales and support channels.

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