Evolving to Automotive Grade
First there was an emitter-detector pair in through-hole packaging that was wave soldered to a printed circuit board. The emitter and detector were facing each other so that if anything came between them, the output current of the photodiode or phototransistor would change. This change would be relayed to a controller and something would happen: a motor would start or stop, an indicator light would turn on or off, or a bag of chips would fall to the bottom of a vending machine.
The Triassic Period
The position of the discrete components was too difficult to precisely control. One would be higher than the other or at a slight angle, the leads would be bent, or during handling they would become disoriented. This posed a problem for the system because the output current from the detector would vary from board to board. The controller was looking for a certain signal level and, without exact orientation, it wouldn’t get it. Then Vishay molded the discrete components in a common plastic housing to ensure exact orientation. This required several different package versions, each with a different gap between the emitter and detector, with a photodiode or phototransistor output, and with a different lead bend for horizontal or vertical gaps. These sensors were called transmissive sensors or slotted interrupters.
The Jurassic Period
With more and more board assemblies going with pure surface-mount components, the leads of the through-hole packages had to be bent so they could also be surface mounted. The plastic used in the housings had to change to withstand the 260 °C reflow temperature. Horizontal slotted packaging did not evolve and remains as only a through-hole package. While many suppliers stopped evolving at this point, Vishay continued.
The TCPT- and TCUT1300X01 Period
Automotive customers needed a transmissive sensor that could operate at higher temperatures and was qualified to AEC-Q101 standards. The molding compound of the emitter and detector limited the operating temperature. Based on the techniques used in Origami, Vishay designed a lead-frame based custom formed sensor that used emitter and detector chips without lenses. With a gap of 3.0 mm and tightly controlled chip placement, the operating temperature increased from a maximum of 85 °C to 105 °C. Following the theory of one detector good, two detectors better, Vishay created a transmissive sensor with two detector windows. With two detectors, steering angle sensors could not only detect an object but could also determine direction and speed, which is critical input to electronic stability control units.
The TCPT- and TCUT1350X01 Period
Ever-demanding automotive customers needed the sensor to operate at still higher temperatures, to work in near-engine compartments and harsh environments up to 125°C. With some nifty design changes, Vishay was able to manufacture transmissive sensors that met this specification.
Has the transmissive sensor evolved to its highest form? Not even close. Early next year, Vishay will introduce an automotive transmissive sensor that will someday have archeologists awestruck and present day Rutronik customers capable of implementing controls that they can only now imagine.