© TT electronics plc
General Note
TT Electronics reserves the right to make changes in product specification without
notice or liability. All information is subject to TT Electronics’ own data and is
considered accurate at time of going to print.
Automatic Calibration Circuitry
OCB100 Series
Issue B.1 04/2016 Page 2
OPTEK Technology, Inc.
1645 Wallace Drive, Carrollton, TX 75006|Ph: +1 972 323 2200
www.optekinc.com | www.ttelectronics.com
Theory of operation:
The OCB100 series is designed to minimize the change of optical devices due to manufacturing variance. This system can be used
to calibrate either reflective or interruptive devices and provide a consistent output eliminating the requirement to confirm either the
LED drive resistance or Phototransistor Load Resistor to provide a consistent output steady state condition. With the OCB100, the
design engineer can narrow the expected startup output state providing a device that will operate the same for years with the same
startup state thus enhancing the reliability and consistence of the system. Degradation of the LED or phototransistor is
compensated for each time the system is calibrated allowing the system to provide a known, consistent output level resulting in
years of consistent quality. The OCB100 series are designed to maintain the calibrated setting even if power is lost. This allows
faster startup without the need for calibration every time the device is initiated. The designer can initiate the calibration procedure
at any time by momentarily grounding J1-Pin-4 (green wire). This allows the device to be remotely calibrated then mounted in the
equipment.
The PCBoard has a set of shorting pins allowing the user to change the phototransistor load resistor. By arranging the shorting bar
to the appropriate location (see table), the load resistance can be changed from approximately 2.5K to 27 K W. Increasing the load
resistor increases the sensitivity of the device.
When the “Calibrate” pin (#4) is momentarily grounded, the system begins its calibration process and raises the current through the
LED, from 0 mA to 14 mA, until the phototransistor reaches the preset calibration point. A green calibration light will blink 3 times
when the preset phototransistor output level is reached. At this time, the LED drive current is locked and maintained until Reset/Clear
pin is grounded. If for some reason, the LED drive current reaches the maximum allowable value, a RED warning light will be turned
on. During the calibration process, remote monitoring of J1-Pin3 allows the designer to ensure the system is calibrated (this output
should be at the preset calibrated output level when the calibration procedure is completed). Adjusting the phototransistor load
resistor may allow the system to calibrate properly.
After the calibration process is complete, the device is ready for acknowledgement of a change in the signal. The design engineer
can monitor either the Analog Output (J1-Pin 5) or Logical Output (J1-Pin 2 or J1-Pin 3).
The Analog Output allows the design engineer to set any reference point to recognize an optical change for the device being
monitored. The Analog Output can be used with reflective devices to monitor small changes in the distance from the device. The
further the target is away from the device, the lower the reflected signal.
The Logical output will change state once the preset optical light condition is reached. The “Logic Out A” switches when the optical
signal increases above approximately 2/3 of V
CC
while “Logic Out B” switches when the optical signal decreases below approximately
1/3 of V
CC
.
As with all optical devices, the switching condition is consistent with the phototransistor receiving a preset light level. This switching
position and light level may vary dependent on several possible factors such as:
• Ambient light variation ((reduced or eliminated with periodic recalibration)
• LED and phototransistor pair degradation (eliminated with periodic recalibration)
• Contamination in front of either the LED or phototransistor (reduced or eliminated with periodic cleaning)
• System power variation (reduced or eliminated with periodic recalibration)
• Temperature changes (reduced or eliminated with periodic recalibration)
The OCB100 PCBoard can be wired directly to any Optical device with an LED and Phototransistor.
• Interruptive devices / slotted switches / interruptive encoders
• Reflective devices / reflective switches / reflective encoders
• Specialty devices / fluid sensors
• Etc.
