42
ALTERNATE ENGINEERING UNITS (AEU) EXPLAINED
The following table shows the relationship between pressure
in psi and pressure displayed in the available alternate engi-
neering units in the DXD. Note that at pressures above zero
it is possible for a selected engineering unit to display well
over the normal 50,000 count limit defined for the DXD. For
this reason, selection of the sensor range and AEU need to
be matched accordingly to limit the resolution of the display
below the 50,000 count resolution limit. As can be seen in the
example table below, resolutions above and below the maxi-
mum limit can be displayed. These highlighted measured
values adhere to display “rules” as defined in the statements
and examples below the table.
UPDATE RATE MODIFICATIONS
The DXD has a “Delta Sigma” Analog to Digital Converter
which gives it the capability of modifying its filtering profile
by the adjustment of data in its non-volatile memory. This is
done by writing to the DXD’s memory via the “ER” and “ew”
commands. Below is a table that lists the necessary informa-
tion to change the update rate of the DXD from 15 to 100
AEU
Measured
Measured
AEU
Neumonic Scaler
psi
AEU Definitions
BA .0689476 5002.5 344.90
Bar
CW
70.433 4055.3
285628
cm water
FW
2.2457 4055.3
9107
feet of water
HP 68.9476 4051.1
279314
Hecto Pascal
IM 2.03602 4033.7
8212
In. Hg
IW
27.73 4014.1
111311
In. Water
KP 6.89476 3980.8
27446
Kilo Pascal
MB 68.9476 3956.6
272798
Mili Bar
MM 51.7149 3938.9
203700
Mm Hg
MP
.00689476
5002.5
34.490
Mega Pascal
NP
N/A
5000.0
50000
Numeric PSI
RULE 1 – The display pressure is not to exceed 50,000
counts of resolution unless the true value of the number is
altered in not doing so.
RULE 2 – Numbers cannot be added to the right of the
decimal point if their addition causes numbers to exceed
the 50,000 count limit.
RULE 3 – Displayed numbers over 50,000 counts will not
increment in single digits. The will increment by a value
calculated by the full scale value divided by 50,000.
1st Rule example, AEU = mm Hg (MM):
3938.9 PSI is displayed as 203700 mmHG. This is over the
50,000 count limit because truncating the number down
to 20370 (below the 50,000 count limit) changes the true
value of the number.
2nd Rule example, AEU = in Hg (MM):
4014.1 PSI is displayed as 8212 in Hg. Adding .6 to the in.
Hg value (8212.6) pushes the value over 50,000 counts.
Removing the .6 does not alter the value of the number, it
just reduces the amount of resolution.
3rd Rule example, AEU = mmHg (MM):
258575/50,000 = 5.1715, therefore the display will incre-
ment in steps of approximately 5 counts.