90074225 MOPS-Q QTH Lamp Pow er Supplies
Page 30
Instructions on how to setup and operate the LIK-LMP with the OPS-Q Power Supply begin on page 30 of
this manual.
The LIK-LMP uses the 75182 detector head, which houses a Thermoelectrically Cooled Silicon Photodiode
as its light sensor. The 75182 outputs a current value directly proportional to the output power of the
lamp. As conditions beyond the power supply
’s control mentioned above begin to change the lamp’s
output, the 75182 relays a different current value to the OPS-Q Power Supply. To keep the lamp output
power constant to the operat
or’s selected preference, the OPS-Q Power Supply constantly changes its
output current/power based on the output current of the 75182. This allows the user to have a consistent,
stable lamp output throughout the entirety of the lamp
’s lifetime.
For any photoconductive device such as the 75182, output current is ideally only the result of input light
on the active area of the detector. However, unavoidable conditions such as ambient temperature and
leakage current cause the detector to output dark current, which is a current output that is not the result of
light incident on the active area of the detector. The predominant cause of dark current is thermionic
emissions, in which the detector outputs a current value as a result of ambient temperature. To
counteract this, silicon photodiode of the 75182 is thermoelectrically cooled, meaning that the light
sensing silicon wafer is mounted on a Peltier cooler. This Peltier cooler maintains the temperature of the
silicon substrate at a temperature of 0-25
˚ C based on the user’s setting of the OPS-Q Power Supply.
Stated simply, a lower silicon detector temperature results in a more accurate light intensity reading. A
more accurate light intensity reading allows the OPS-Q Power Supply to more accurately determine the
proper current/power to supply to the lamp to keep output power constant.
To change the temperature of the 75182, press the horizontal menu button under the Setup icon on the
LCD interface until the vertical menu showing CoolTemp, Idle, and Autoset appear on the right as shown
on the next page.
Figure 12 Setting the TE Cooler Temperature
When the menu above appears on the LCD interface, press the vertical menu button next to CoolTemp.
The knob on the front panel of the OPS-Q Power Supply can then be used to select a detector temperature
from 0-25
˚ C. The temperature initially shown when this menu is accessed is the temperature set during
the last operation involving the use of the 75182.
