The Operating Range of the Rate Converter
The purpose of the rate converter is to provide trigger pulses to the camera reflecting the frequency of the encoder pulse train multiplied by a fixed amount.
The rate converter will operate in a certain frequency range. We can introduce three equivalent ways to express the operating range of the rate converter.
- The minimum and maximum operating web speed,
- The minimum and maximum operating encoder frequency,
- The minimum and maximum operating camera line frequency.
The third item (camera line frequency in Hertz) has been chosen to represent the speed performance of the line scan system fitted with an encoder and using the Grablink rate converter.
As seen on the picture, the user should use the rate converter in the recommended working area. Inside the valid working area, the rate converter will loose its precision if approaching from the prohibited area. The values are too much different:
- too small input (< 10 Hz) means that the encoder gives too few pulses to obtain any accuracy at the output.
- too high input (> 100 kHz) cannot be generated by an encoder. It must be anyway divided by a too large number to give correct camera pulses.
- too small output (< 10 Hz) means that the line-scan camera receives not enough pulses.
- too high output (> 100 kHz) cannot be followed by a line-scan camera.
As the user can check, those limits are quite exceptional.
The operating range is defined as follows:
It is usually above 200, but depends on the value actually entered to program the rate converter.
The user should ensure that the operating range adequately covers the need of his web inspection application. MultiCam parameters are provided to achieve this check.
The speed limit is imposed by the camera readout process or by the minimal exposure time.