What is Bicone?
What is the "BICONE" method?
The "BICONE" or double-cone measuring method is an optical measuring method for determining the distance from a measuring object in reflective light operation with special fiber optics.
BICONE method without reference branch
This method uses a fiber optics bundle whose fibers are divided into two segments (transmitter and receiver segment) that are arranged directly beside each other or at a certain distance from each other.
Typical fiber optics frontends:
Typical fiber optics frontends:
Double fiber optics arrangement
Light (from an LED or laser diode) is now supplied through the transmitter fibers:
A part of the light that is reflected from the object surface impinges on the fiber optics frontend again, and the part of the light that impinges on the receiver fibers at an angle not exceeding their numerical aperture (intake angle range) reaches the receiver (e.g. a photodiode).
The area that is covered by the light cone of the transmitter, and the receiving cone that is defined by the maximum receiving angle (determined by the NA (numerical aperture)), form an exact intersection (overlap area).
When the object distance increases, the light received by the receiving branch first increases and then, after reaching a maximum value, decreases again. The signal increase on the receiver section with increasing distance is caused by the increasing intersection of the overlapping transmitter and receiver cones. The following decrease of the receiver signal is caused by the decreasing light quantity that impinges on the fiber optics area of the receiver with increasing distance. When the light that is directed onto the object by the transmitter fiber optics impinges on the object, it is in part diffusely reflected into the complete half space, but even with directly reflected light (highly reflective surfaces) the receiver signal decreases with increasing distance. Fortunately the receiver signal first increases proportionally, i.e. linearly, with increasing object distance, and then linearly decreases again after reaching a maximum value.
The increase is much steeper than the following signal decrease.
For a clear interpretation of the receiver signal a decision must be made for an application whether to use the close range (fast signal increase, therefore higher accuracy, but smaller available measurement range), or the far range (slow decrease of the receiver signal, reduced accuracy compared to the close range, but relatively large measurement range). The area around the maximum signal value should be avoided.
Since this measuring method is a so-called energetic process, it is imperative here that after calibration measurement always is performed on the same (and constant) surface.
BICONE method with reference branch
If, however, the measurement surface changes, a so-called reference receiver must be used. The reference branch is used to evaluate the reflection behaviour of the measurement surface. Signal evaluation thus is normed, i.e. in relation to the reference signal:
Because of norming the signal increases almost linearly in relation to the object distance. A differentiation between close and far range is no longer necessary here.
Sensors for the BICONE method without reference branch
The SPECTRO-1-FIO sensors are high-precision, temperature-compensated evaluation units that can be parameterised with a PC and customer-specifically calibrated and linearised by means of a conversion table. Various fiber optics and light sources (IR-LED, UV-C-LED and white-light-LED) also are available.
The SPECTRO-2-FIO sensors are high-precision, temperature-compensated 2-channel systems. One channel (in combination with the BICONE fiber optics) functions as reference branch here. The sensor system can be parameterised using a Windows® user interface, and can be customer-specifically calibrated and linearised by means of a table.
Various fiber optics are available for different light sources (UV-C, IR, white-light) and distance ranges.