User Manual
9
6.1 Visual Inspection
•
Make sure the optical windows are clean.
•
Inspect the cables and connectors for any damage or corrosion. If you see a
discoloration on the white co-axial cable, you may suspect that the cable has
water damage.
6.2 Testing the Source Tube
The source tube is the longer of the two tubes. You can check to see if the source
tube is working properly by performing the test explained below.
First, make sure the UV light is emitted from the source tube. To do this, you
may look into the source tube (the longer of the two tubes), and you should see a
bright blue light emitted from it.
Avoid looking into the source tube for an extended period of time
when the KH20 is powered on to minimize the prolonged exposure
to the UV light.
If you see a faint or flickering blue light, perform the following test.
Check the current drain on the KH20
Typical current drain for the KH20 during normal operation should be
15 ~ 20 mA. The current drain of around 5 mA or less indicates the problem
on the source tube. Obtain an RMA from Campbell Scientific, Inc. and send
the unit in for repair.
Check the voltage signal output from the KH20
If the voltage output reading is below 50 mV, you may have problems with
either the source tube or the detector tube. For the detector tube testing, see
Section 6.3 below.
6.3 Testing the Detector Tube
If the source tube tests fine but the output from KH20 is still in question, perform
the following test. Prepare a piece of paper and insert it between the source tube
and the detector tube to completely block the optical path. You should see an
immediate decrease in the voltage reading, and it should go close to zero. No
noticeable change in the voltage output, when the optical path is completely
blocked, indicates a problem in the detector tube. If the decrease in the voltage
reading takes place but the reading remains below 50 mV, when the paper is
removed from the optical path, the source tube may be at fault. Obtain an RMA
from Campbell Scientific, Inc. and send the unit in for repair.
6.4 Managing the Scaling of KH20
The KH20 cannot be used to measure an absolute concentration of water vapour,
because of scaling on the source tube windows caused by disassociation of
atmospheric continuants by the ultra violet photons (Campbell and Tanner, 1985
and Buck, 1976). The rate of scaling is a function of the atmospheric humidity.
In a high humidity environment, scaling can occur within a few hours. That
scaling attenuates the signal and can cause shifts in the calibration curve.
NOTE
