Cosa XPDM, Руководство пользователя

Страница: 11 / 26

11
5.2 Operating State
Refer to Appendix A for a flow diagram of the operating state. The XPDM is powered ON
by pressing the ‘Power’ button until a beep is heard; to activate the backlight, continue to
depress the ‘Power’ button until the backlight turns on. Keep in mind that with the backlight
on the unit consumes about 5 times more power. Upon power up the unit performs certain
initialization tests (see section 9), and enters the ‘Operating State’, in the Viewing
Dewpoint mode. Depressing the ‘Mode’ button will change modes in the following order:
Viewing Dewpoint
➜
Viewing Sensor Temperature
➜
Start Autocal
➜
Viewing Serial Number
➜
(back to) Viewing Dewpoint. The unit will
return to Viewing Dewpoint mode if no buttons are pressed for 30 seconds, unless it is
performing Autocal.
5.2.1 Viewing Dewpoint Mode
In this mode the user can view the dewpoint, signified by the presence of the ‘DEW
POINT’ legend on the lower left of the display. The available engineering units in which to
view the moisture content are °C, °F, PPM, LBS and G/M
3
; the up and down buttons scroll
back and forth through these units in respective order. The °C and °F are dewpoint
readings. The ppm is parts per million by volume computed at the sensor pressure (more
about pressure later). The Lbs and G/M
3
are pounds of water per million standard cubic
feet and grams of water per standard cubic meters, both in Natural Gas, they are com-
puted according to data derived by IGT Research Bulletin 8, taking into account sensor
pressure. A short press of the ‘pressure correct’ button toggles the unit in and out of
pressure correct mode. When there is no pressure correction applied the PSI legend does
not appear. The PSI legend flashes at the bottom of the display, when there is pressure
correction in the computation of the displayed values. Pressure correction is used in the
context that the values displayed signify the moisture content at some pressure (we refer
to this as the ‘Gas Pressure’) different than the pressure at the sensor. Note that PPM,
LBS and G/M
3
readings are by definition unaffected by pressure correction because only
the pressure at the sensor affects their value. While °C and °F are affected by pressure
correction by reporting what the dewpoint would be at the Gas Pressure when the
dewpoint is what is measured at the pressure at the sensor. However, this also implies that
whether pressure correction is applied or not the PPM, LBS and G/M
3
readings are
affected by the setting of the sensor pressure. Sensor pressure is used in the context that
this is the pressure inside the sampling chamber when performing the measurement. Gas
pressure is used in the context that this is the pressure to be used in computing what the
dewpoint would be at a pressure different than the one in the sampling chamber. A long
press of the Pressure Correct button, while in the pressure correct mode (flashing PSI
legend), changes the unit to the View/Set Sensor Pressure sub-state. The display
has the
‘SET’ and ‘PSI’ legends on and alternately shows
SEN
and the currently set value for the
sensor pressure. The up and down buttons allow the user to modify the sensor pressure,
while a short press of the pressure correct button toggles the Sensor Pressure setting
between whatever value is on the display and 14.7 psi ---- this is a quick way to go back to
atmospheric settings. A long press of the pressure correct button changes the unit back to
the Viewing Dewpoint Mode. Pressing the ‘Mode’ button changes the unit to the View/Set
Gas Pressure sub-state. The display has the ‘SET’ and ‘PSI’ legends on and alternately
shows
GAS
and the currently set value for the gas pressure. The up, down and pressure