Alicat PCU Portable Calibration Unit - Manual (Page 7)

7
Operating the PCU
The meter for each flow range on the PCU is controlled by its own set of Display/Control electronics
located above the inlet and outlet ports of each flow range. The PCU meters can have several screen
“modes” depending on how the device is ordered. All PCU meters have a default Main Mode, Select
Menu Mode, a Gas Select Mode (the Gas Select Mode may not be available on meters calibrated for a
custom gas or blend), a Communication Select Mode, a Manufacturuer Data Mode and a Miscellaneous
Mode. In addition, your device may have been ordered with the optional Totalizing Mode (page 27). The
device defaults to Main Mode as soon as power is applied to the PCU.
Main Mode
The main mode screen defaults on power up with the mass flow on the primary display. The following
parameters are displayed in the main mode as shown in Figure 2.
PSIA o C Tare
+13.49 +22.73
MASS
SCCM
Air
+0.000 +0.000
Volume Mass Main
Figure 2. Main Mode Display
The “MODE” button in the lower right hand corner toggles the display between the Main display and
the Select Menu display.
Tare – Pushing the dynamically labeled “Tare” button in the upper right hand corner tares the flow meter
and provides it with a reference point for zero flow. This is a simple but important step in obtaining
accurate measurements. It is good practice to “zero” the flow meter each time it is powered up. If the
flow reading varies significantly from zero after an initial tare, give the unit a minute or so to warm up
and re-zero it.
If possible, zero the unit near the expected operating pressure by positively blocking the flow downstream
of the flow meter prior to pushing the “Tare” button. Zeroing the unit while there is any flow will directly
affect the accuracy by providing a false zero point. If in doubt about whether a zero flow condition exists,
remove the unit from the line and positively block both ports before pressing the “Tare” button. If the unit
reads a significant negative value when removed from the line and blocked, it is a good indication that
it was given a false zero. It is better to zero the unit at atmospheric pressure and a confirmed no flow
conditions than to give it a false zero under line pressure.