5.2. Additional technical info and definitions
For the detailed technical description and specification of the epc610 chip, refer to the corresponding Datasheet epc610.
Below are some technical considerations to help better understand the working principles and boundary conditions:
Maximum AC input illumination power
This is the amount of the backscattered modulated light, that leads to a saturation of the signal processing path. The camera goes “blind”.
This value is also a function of the relative spectral sensitivity (e.g. refer in the datasheet to the table “Sensitivity and ambient-light sup -
pression vs. wavelength”).
Minimum AC input illumination power
This is the minimal amount of the backscattered modulated light to provide just enough signal. Below this level, the distance noise can in -
crease significantly. This value is also a function of the relative spectral sensitivity (e.g. refer in the datasheet to the table “Sensitivity and
ambient-light suppression vs. wavelength”).
Integration time
During this time, the sensor is sampling the light power. A longer integration time leads to a higher sensitivity of the camera. This means a
weaker illumination can be used. Use this to trade-off between achievable measurement range and illumination power.
Dynamic range at a fixed integration time
Is defined by the span between the maximum to minimum AC input illumination power limits.
Extended dynamic range
By an on-the-fly adaption of the integration time to the illumination conditions of the scenery, the dynamic range of the system can easily
expanded.
Unambiguity distance
epc TOF devices are operated with a periodically (e.g sinusoidal) modulated illumination. The unambiguity distance is the distance that
corresponds to the traveled distance of light within one modulation period. Light signals inside this time window can be allocated to a
unique distance. Reflected light with a longer travel time will cause false readings (because the sensor cannot distinguish between differ -
ent modulation periods).
Illumination of the scenery
Is the light actively brought into the observation area by the camera's modulated light signal.
Remission (more commonly known as reflectivity)
The emitted light from the camera is backscattered by the object in the scenery. The surface conditions of this target define how much light
will be reflected. This loss of light power is defined by the remission factor (or reflectivity)
Examples: A sheet of white paper has a remission of 90%, whereas a dark carpet reflects only 5%.
Ambient-light suppression
In real world applications, there will always be ambient-light. The epc610 3D TOF Imager is designed to filter out such ambient-light from
the received signal (ambient-light suppression). This internal filtering capability works so well that the systems even operates in highly illu-
minated scenes such as outside applications in bright sunlight. However, there is a limit for this suppression. E.g. a measurement attempt-
ed directly towards the sun will fail because of saturation.
The ambient-light suppression also depends on the relative spectral sensitivity (e.g. refer in the datasheet to the table “Sensitivity and am-
bient-light suppression vs. wavelength”).
Distance offset
There is always a distance offset that is made up by the sum of all delays in the signal chain of the chip. Like any other camera system,
TOF systems need be offset-calibrated before they are put into use.
6. Further Application notes
6.1. Illumination
Good illumination is crucial, as is the design of the Rx and Tx lens system. epc provides several application notes on this topic. However,
an LED illumination subsystem and the matching Rx and Tx lens systems requires adequate experience.
6.2. Ambient-light & wavelength
Ambient-light is by nature a disturbing factor. There are several options to suppress such interferences in an application. One solution is
the use of modulated light, which can easier be separated from typical static (DC) ambient-light. Another widely used approach to increase
the ratio of the signal to the ambient-light is to work with specific wavelengths. Sunlight and artificial light sources typically have low in -
frared (IR) power. This is the reason why epc detectors have high sensitivities in the near infrared range (NIR). Sensor systems based on
epc detectors should therefore be designed to work in the NIR Range (e.g. 940nm).
6.3. Noise reduction
The accuracy of the distance readings depends on the signal amplitude in the receiver path. The higher this amplitude, the more accurate
the results, the less distance noise occurs. The signal amplitude is equal to the product of the received light energy multiplied by the inte -
gration time. The adaptation of the integration time to the highest possible signal values (including a certain safety margin to avoid channel
saturation) leads to noise reduced measurement values.
© 2014 ESPROS Photonics Corporation
Characteristics subject to change without notice
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Manual epc610_Camera - V1.5
www.espros.ch