QVE00033
The internal construction of the sensor is based on subcomponents with a lens structure on both sides (emitter and detector). As a result, the flux of infrared light between the emitter and the detector is optimized and guarantees operational conditions compatible with low consumption and low voltage supply. For a driving current of only 5mA the collector current under 5 volts VCC is greater than 0.1mA.
The device is offered in a surface-mountable leads configuration. Its mass configuration and footprint make it very stable in its natural standing position. It also comes with a tape bridging the space between the two towers to facilitate the pick and place. It is able to withstand a standard reflow process of 200°C for 60 seconds with a peak at 240°C
The sensor features an aperture of 0.4mm on both sides (emitter and detector) centered on the optical axis of the device, which confines the useful infrared flux to a narrow beam between the emitter and the detector. This provides two essential benefits:
1) Response sharpness: The output signal response to a knife edge moving in and out of the gap, vertically or horizontally (see fig. 1 and fig. 2 in the datasheet) changes from 10% to 90% for a 0.4mm displacement. That value determines the resolution of the device, which is an important parameter in application such as encoders.
2) Immunity to parasitic light: The aperture blocks the side rays from the emitter and the resulting parasitic reflexions to the detector. This increases the noise level on the response and may contribute to false triggering.
The detector is encapsulated in a daylight filtering resin that reduces the sensitivity of the device to ambient light. This also contributes to a lower noise level and a better signal-to-noise ratio. The result is an ability to operate at low input current, enhancing the low power consumption in the application.
This optical switch is designed to indicate the presence or absence of a vane or shield that has been placed in the emitter to detector path. Under normal or non-blocked operation the LED shines IR light on the phototransistor. This received light develops a photocurrent in the phototransistor. This photocurrent can be converted to a logic control indicating the aperture is not blocked. When a shield or other IR opaque material is used to interrupt the light path between the LED and the phototransistor, the phototransistor photocurrent is reduced to zero. This extremely small value of photocurrent can also be converted to a logic compatible signal indicating the optical path in the slot has been interrupted. This switch provides high mechanical sensitivity. Once the vane has moved to the center of the optical aperture a movement of only 0.4mm will cause the detector path to be interrupted.
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Interfacing The QVE00033 is compatible with all families of CMOS logic (3.3V, 5V, and 15V). Compatibility with TTL logic families is possible when a buffer or amplifier is connected between the phototransistor and the logic gate. The LED IR emitter is commonly operated continuously. Thus forcing a DC current continuously through the LED minimizes any aliasing or timing issues when the output of the switch is interrogated by a microprocessor or microcontroller. The LED is connected to the DC supply via current limiting resistor (680W). Common Emitter Configuration Figure 1 shows a connection called common or AC grounded collector phototransistor amplifier. As the graph below the schematic shows, the logic output is low or "0" when the path is blocked. This is because the blocked phototransistor is conducting very little current, and the 68K load resistor pulls the input of Fairchild TinyLogic™ buffer low. As the shield is pulled out of the interrupter's throat, the 0.4mm aperture is exposed and IR light falls upon the phototransistor. This light generates a photocurrent that flows from the collector to emitter of the phototransistor. This increase in current develops a voltage across the emitter load resistor. |
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Figure 1. Shield Distance |
