The X-ray tube in focus

The RFM (Real-time FocusMeter) is a tool for determining the X-ray tube focal spot in a quick and easy way. No film is needed and the method is simple. The greatest advantage of using this technique is the speed - in less than one minute a complete examination is carried out which gives you both the size and shape for different generator settings. The result of a measurement is available immediately and can be examined and displayed on a computer screen. The method makes it possible to measure, for instance, the focal spot width and length for different angles from the radiation beam axis. With this method it is also possible to measure focal spot down to 100 µm.

Measuring method

The RFM is based on the slit method according to the IEC 60336 recommendation. The 10 µm wide slit makes it possible to measure focal spot sizes down to 0.10 mm, according to IEC 60336.

The RFM can be automatically aligned. With a specially designer alignment pattern, and four CCD arrays, the RFM determines its position in the beam. It also calculates the enlargement factor and the distance from the focal spot to the detector.


Two main accessories are available. The R100 Trig detector to start and stop measurements automatically, and the RFM pro holder (used by world leading X-ray tube manufacturers). It expands the use of the RFM when a higher degree of accuracy and repedibility of the positioning is required for example, when doing absolute measurements in an X-ray tube production line.

Supporting standards IEC 60336 and NEMO XR5
Tube focal spot types Radiographic, CT, Mammographic, and dental
Exposure time Minimum 10 ms
kV range 22-150 kV
Charge range, tube 10-100 mAs (at 70cm)
Enlargement factor 0.8-5 (automatically calculated)
Measurement range 0.1-5 mm
Resolution 25/E µm (E = enlargement factor)
MTF magn. factor 1 < M < 10
Measured values Focus IEC 336 (or DIN or NEMA) focus RTI (length and width)MTF at -3 dB, M=2 RMS (Root Mean Square)
Alignment system Automatic
Trigger System                       
Trigger modes Automatic (with external trig detector), Auto start, adjustable delay and window.Manual start, adjustable window
Delay 0-50,000 ms
Window 10-50,000 ms


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