UEi Test Instruments AK900SC - Manual (Page 18)

18
The absolute zero function
This gives the 900 the ability to zero the pressure readouts to absolute
zero and thus read out accurately in high altitude locations. In order
to take advantage of this function you will need to put the 900 into the
o
F/psia mode and then with both the low side and high side connected
to a vacuum pump at 100 microns or less (the lower the better); press
the zero key and hold it down for 4 seconds. The unit will then read 0
psia and reference every other pressure to that so that a high elevation
atmospheric may read 3”Hg. with the hoses open to atmosphere. In
order to go back to the factory settings, select
o
F/psig and again press
and hold down the zero key for 4 seconds.
Dual Temperature Sensors and Delta T
The last feature enhancement is the dual temperature sensor assembly
and the ability to switch not only back and forth between SH and SC
but to read a ‘dt’ or delta temperature as the blue lead (SC) sensor
temperature is subtracted from the red lead (SC) sensor. The blue
sensor is the SH sensor as it is always associated with the low side
and the vast majority of SH settings are taken for the evaporator
superheat. Remember; blue=low side=superheat for evaporator
whereas red=high side=subcooling for the condenser. The
temperature “t” mode is always accessing and referring to the blue
sensor.