Feature：
• Reduce long and short term variations in lamp output
• Ensure accurate timed exposures
• Dose control
• RS-232 communications
• Works with Oriel Solar Simulators and Flood Exposure Sources

The 68951 Digital Exposure Controller is a light intensity controller and digital timer in one package. It maintains a constant light level and allows preset timed or dosage based
exposure control. For those not requiring a light intensity controller or dose control, we offer a stand-alone digital timer, model 68945. Both instruments may be controlled via a
PC through an RS-232 interface.

The 68951 and 68945 support our Large Area Illuminators, Solar Simulators and Flood Exposure Sources. For light intensity control instruments for our small area illuminators,
see page 277.

Digital Exposure Controller
Our sources have highly regulated power supplies to operate the lamps at constant power or current. However, with aging of the lamp and variables such as electrode erosion, gas
absorption or desorption, the light output can change. These changes tend to be wavelength dependent. The 68951 Digital Exposure Controller works with the power supply to compensate for these changes and ensure a stable, long-term output. See Fig. 1 for an example of the effect of the 68951 on the light output of a kW Solar Simulator.

Fig. 1 The effect of the 68951 Digital Exposure Controller on the output of a 1000 W Solar Simulator.

How it Works
The 68951 is made up of a light sensing head, a controller, and a fiber optic probe. The silicon based light sensor monitors part of the light source output (via the fiber probe), and
the controller constantly compares the recorded signal to the set level and changes the power supply output accordingly to keep the measured signal at the set level. Automatic
detector gain setting allows the unit to work with 300 to 1600 W Large Area Illuminators.

Built-in Digital Timer
The 68951 also allows timed exposures. The 68951 is capable of exposure times from 10 ms to 9999 hours, in increments as short as 10 ms. However, the mechanical response time of the shutter in our Solar Simulators limits the minimum exposure time to 100 ms, and the shortest interval between exposure to 80 ms. For those instances when a timed
exposure is not sufficient, you can use the auto-dose mode to keep the shutter open until the total flux equals a user set value.

Stand-Alone Digital Timer
If timed exposures are required without the need for ultra constant light output, purchase the 68945 Digital Timer. Just like with the 68951 Digital Exposure Controller, the 68945
Digital Timer allows exposure dosages from 10 ms to 9999 hours, in 0.1 second intervals. Note: the Illuminators' mechanical shutter limits the exposure times to 100 ms, and the
shortest interval to 80 ms.

Accessories
You can remotely control the 68951 or 68945 via a push button switch, model 68955.

Ordering Information

Fig. 2 Diagram showing the probe assembly from the 68951 Digital Exposure Controller, mounted to a Solar Simulator Housing.