The MIO (measurement input & output) interface is a special feature of the IRCAM pro cameras. It permits high-precision acquisition, digitizing and processing of external signals and generation of control signals for external devices. The novel technology of the MIO interface guarantees absolute synchronicity of camera and other devices or external signals, respectively. The integration into the camera makes this solution very compact and user-friendly.

Analog input:

• 2 independent channels (synchronous A/D conversion)
• resolution: 24 Bit
• differential inputs
• input voltage ranges: 1 V, 2,5 V, 5 V, 10 V
• 8 conversions per frame (conversion time user-configurable)
• Conversion results are directly written into the image data

Digital output:

• 2 channels
• Generation of trigger and lock-in reference signals (timing user-configurable)
• Opto-isolated, open collector
• Digital input
• 2 channels
• Functions: Trigger for integration time start, reset frame counter
• Opto-isolated
  

Benefits and advantages:

When using IR imaging for non-destructive testing, very often a time-dependent temperature change is generated in the sample under test by an excitation source. The measurement principle requires that the excitation source be synchronized with the image acquisition and that the excitation signal is exactly time-correlated with the images acquired. With the MIO interface an analog reference signal derived from the excitation source is digitized at well defined moments and written as digital data directly into the image data. With the integration of the MIO interface directly into the camera a very high temporal precision of better than 1 µs is reached, whereas with other common solutions with separate analog acquisition it is rather > 10 ms. Particularly for fast processes, this is a huge advantage.

The MIO interface can also generate configurable signals for controlling excitation sources. These signals can be used as well for pulse thermography as for lock-in measurements. Applying the lock-in technique is often necessary when measuring very small signals (e.g. minute temperature variations). With the lock-in technique the measurement signals are integrated over a longer period of time, weighed with their respective phase relative to the reference signal. The result is an IR image with strongly improved signal-to-noise ratio which permits thermal resolutions of the order of a few Microkelvin. This is some orders of magnitude better than the nominal NETD of the IR camera. Moreover, with lock-in the phase shift between excitation signal and thermal response can be measured and heat sources can better be localized.

The MIO interface, thanks to its high temporal precision, is particularly suitable for lock-in measurements with high excitation frequency and for applications with the so-called "undersampling" for maximum temporal resolution. Arbitrary excitation signal forms and frequencies can be used. The software performs the adaption to the excitation signal automatically, i.e. it is "self-tuning". A good example for the application of the MIO interface is the "thermoelastic stress analysis (TSA)". With TSA, the sample under test is subject to a well defined force which may be periodical. The thermoelastic effect causes an instantaneous temperature variation which is proportional to the internal stress variation. Since the temperature variation is very small for solid bodies, the lock-in technique must be applied to measure it with an IR camera. Synchronous to IR image acquisition a reference signal is generated with a force or position sensor and is digitized. By summation over a number of images, weighed with the reference signal, a greatly noise-reduced high-resolution image of the mechanical stress is obtained.