Edgetech PPM1, Operator'S Manual, Page: 13 / 29

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NOTE: IT IS GOOD PRACTICE TO INSTALL A SHUTOFF VALVE ON EACH
SIDE OF THE MEASUREMENT CELL, TO KEEP IT DRY WHEN OPENING
THE SAMPLING SYSTEM.
5.2 MEASURING DRY GASES
5.2.1 MEASUREMENT TIME
Measuring extremely dry gases is an art. Time and patience are involved. If you
are in a hurry, you may not obtain accurate results. As discussed above, all
materials are hygroscopic. That is, they have pores that retain water molecules.
When the level of moisture in a gas is decreased, for example, it may take a very
long time for all of the materials in the entire sampling system to outgas, or give
off all the excess water molecules that are trapped in the pores of every inside
surface of the system. Depending upon your unique conditions, it could take a
number of hours for complete stabilization of the moisture level in your gas. Be
sure you wait long enough before taking readings.
5.2.2 MATERIALS
As discussed in the Installation chapter of this manual, selection of materials is
extremely critical for proper dry gas sampling. For dry gas measurements, do
not use PVC or other porous tubing.
Some plastic tubing such as Impolene™
may be used for gases in the higher ppm ranges. For measuring gases in the
lower ppm ranges, only stainless should be used.
If readings do not seem to stabilize after waiting a reasonable amount of time,
check to see if you have a leak from outside the system where the vapor
pressure is higher, or have excessively hygroscopic tubing, or possibly your
stainless tubing is contaminated and requires cleaning.
5.3 OPERATING THE INSTRUMENTS
5.3.1 THE PPM1
There are no controls to operate on the PPM1. The operator simply monitors the
digital display, or allows the analog and digital outputs to communicate with the
data acquisition system. When you first turn on the system, a short self-check
period occurs on the display, and then it quickly starts to show the two moisture
parameters that it is programmed to display. These are changeable in the field,
as shown in the following section on the Serial Port. The digital displays, as well
as the electrical outputs, are constantly updated.
5.3.2 THE PPM2
The PPM2 is a portable version of the PPM1. It is necessary to charge the built-
in batteries before using it, and then to recharge them periodically. The charger
is supplied with the system.