Calibration – High Precision & Lower Cost

Why does an individual calibration pay off?
Measurement devices for lasers are used in many different applications and industries, which means a vast amount of calibration regulations. While regular calibrations are mandatory in the medical sector, they tend to be neglected in other industries. It's important to understand that calibration not only ensures the quality of the measurement in terms of repeatability; the individual calibration of a measurement device can also increase its absolute measurement accuracy. Let us start at the beginning.

How is an Ophir sensor calibrated?
Once a sensor is sent to one of our calibration laboratories, our trained technicians carefully check and document its status. The first step is to conduct a visual inspection and perform a comparative measurement with the NIST or PTB traceable calibration master in the lab. Afterwards, the sensor gets cleaned. Records are kept with any discrepancies related to the sensor.

As the spectral sensitivity of the absorber used for the power and energy measurement is not fully linear, Ophir sensors get calibrated by default with more than one wavelength. All spectral areas the sensor's specifications cover are tested no matter which of the calibrated measuring ranges are used by the customer. If the spectral sensitivity of a sensor is flat in a certain area, calibration will be performed within the area and not with a discrete wavelength. Thermal sensors with a power linearity of 1-2% are usually calibrated with an absolute accuracy of +/-3%. Here, the mistake is often made to summarize accuracy and linearity, but actually the mistakes are summed up with a "Root middle-square" function.

If the calibration can be performed without limitations, the sensor will be returned to the customer together with the calibration certificate. In case the evaluation of the sensor shows any anomalies, the technicians provide recommendations for the servicing of the product, if necessary. These recommendations may include such actions as an additional cleaning procedure, cable or battery replacements, or other remedial actions, and will be sent directly to the customer for discussion and approval.

Calibration – High Precision & Lower Cost
Figure 1: Absorption of different thermal sensors.

What is an OEM sensor?
Generally, a sensor is defined as an OEM sensor as soon as there is any deviation from the standard sensor characteristics in terms of technology, construction, or calibration. If the customer uses the Ophir sensor only for certain wavelength, it is – in most cases – worthwhile defining it as an OEM sensor with an individual calibration. This sensor will get an individual part number with a separate calibration documentation that will be added to our global data base. As soon as a sensor will be sent to one of our Ophir labs, the technicians perform the calibration based on that procedure. Herein, it might be documented that the sensor will be calibrated on certain points of one wavelength instead of checking only one calibration point for each wavelength.

Where are the benefits of an OEM calibration?
An OEM calibration brings along significant economic and technical advantages for the customer. In terms of costs, defining an OEM sensor pays off as soon as one or more sensor of that type needs to be calibrated regularly. While the initial definition as an OEM sensor and the creation of the individual part number requires a fee, the costs per calibration are lower. The whole process needs less organizational effort on the customer side as well as in the lab, and both reliability and security are gained.

With an OEM calibration, the absolute accuracy of the sensor can technically be increased. The absolute accuracy of a power sensor mainly depends on the optical characteristics of the absorber coating in terms of its spectral behavior. Ideally, the sensor coating should have a flat spectral response; in reality, significant deviations in the response of the sensor can be seen with different wavelengths. In order to achieve an overall high absolute accuracy of the standard sensor, it needs to be calibrated at several wavelengths. Depending on the sensor type, Ophir sensors deliver an absolute accuracy compared to NIST or PTB-certified standards between 3-5%. With the OEM calibration as described above, all wavelengths that are not used by the customer will not be considered in the calibration process. The absolute accuracy can thus be optimized to 2-2.5%.

Laser power or energy sensors are often used in quality inspection. Regularly testing the sensor ensures and documents that all measurements are reliable and comparable. Any deviation of the laser beam can thus be detected directly and the production of faulty parts or waste of resources is avoided. Additionally, the individual OEM calibration of the sensor further increases the absolute measurement accuracy for specific applications. For further questions, please contact your sales engineer or our service team.

Read TutorialRead as PDF