Harta’s
Low light reference system utilizes our patented linear optical attenuator,
as opposed to using neutral density filter. This attenuator enables one
to reliably and easily attenuate a light source to any level, linearly, down
to the lowest limit of Photo Multiplier Tube (PMT) detection capability.
This
system enables us to provide multiple light points attenuated to any level,
from a level that saturates the PMT, down to the PMT’s lowest limit of
detection, and any levels in between. This provide a way to verify or validate
the PMT / detector’s Dynamic Range and Sensitivity limit.
Dual
light sources provides a way to verify the funcion of the plate. Any errors will result in clearly visible aberrations on the plot.
Our current
plate has 8 light points. Seven of these light points come from an
electronically feedback-controlled light source, which will maintain
a constant light output as long as there is sufficient battery power.
The other light point comes from a separate but identical light source,
but this light will be cut off once the battery voltage falls below a safe
operating voltage. When the reading from well #8 drops, it is time to replace the battery.
The light from the first source is then attenuated using our patented linear optical
attenuator, to provide seven different levels of light points. Since these
seven light points comes from a single source, once they are set, they
maintain a constant ratio. These seven points provides a convenient set
of light levels to verify the linearity of the detection system. When the plate is
healthy, the ratio of the seven light points and the 8th point should be constant,
when it is not, it is an indication that the plate may be defective, or there may be
other problems with the luminometer itself.
A switch
and an LED is provided to check the battery level, when the switch is pressed
and the LED is ON, the battery level is OK.
Power
is provided by high capacity Lithium Batteries, with shelf life of over
10 years.
The body
of this reference plate is CNC machined from a solid billet of aircraft
grade aluminum, to guarantee dimensional stability. The body is then black
anodized to give it a long lasting finish, and resistance to discoloration.
For more information please
contact
us.
Click
here to view a PDF information sheet (requires Adobe Acrobat Reader)
Explanation
of attached plots:
-
(Light plate 2) is a plot of
several readings, where the secondary light source (point 8) fail over
a period of time, the first 7 wells stay constant.
-
(Light plate 1) is a plot of
a perfectly functioning plate, all light points stay constant
-
another plot of perfectly functioning
plate
-
plot of a plate with decaying
batteries, below the level allowed by battery check system. In this plot,
the secondary light source (point 8) is constant.
Plot 3, perfect light plate
