Specifying A Constant's Engineering Unit With Type Suffixes; Time Constants - Emerson E2 Einstein User Manual

unitless numbers. In other words, a "3.0" in an equation by
itself is not assumed to be 3.0 degrees or kilowatts. How-
ever, when used with a function or operator that involves
inputs of a specific type, the result of the operation or
function will use the inputs' engineering unit designation.
For example, if analog input AI6 is a 0-100% humidity
sensor that is currently reading a humidity of 50%, the
result of the equation "AI6 / 5" will result in an output
value of 10%, even though the number 5 has no unit.
2.2.2 Specifying a Constant's
Engineering Unit with Type Suffixes
Occasionally you may want to be specific about a con-
stant's engineering units. The equation parser supports the
use of a type suffix at the end of a constant to specify a
particular engineering unit. Table 2-6 lists all type suffixes
recognized by the Flexible Combiner's equation parser.
Type suffixes must be placed directly after the constant
with no spaces in between the constant and the suffix (i.e.
75DF, not 75 DF).
Suffix Unit
DF degrees F
DC degrees C
DDF delta degrees F
(use this suffix
for offsets)
DDC delta degrees C
(use this suffix
for offsets)
DFH °F per hour
DFC °C per hour
DFM °F per minute
DCM °C per minute
INW inches of water
CMW cm of water
PSI pounds per
square inch
BAR bars
KPA kilopascals
PA pascals
RH relative humidity
FPM feet per minute
Table 2-6
- Type Suffixes for Flexible Combiner Constants
Constants
Suffix Unit
% percent
W watts
KW kilowatts
WH watt-hours
KWH kilowatt-hours
FTC foot-candles
LUX lux
PPM parts per million
OHM ohms
RPM revolutions per
minute
RPMM RPM per minute
DINW differential
inches of water
DCMW differential cm of
water
DPSI differential pres-
sure in PSI
DBAR differential in
bars
DKPA differential in
kilopascals
Suffix Unit
MPM meters per min-
ute
MPS meters per sec-
ond
GPM gallons per min-
ute
LPS liters per second
CFM cubic feet per
minute
CMS cubic meters
per second
V volts
A amps
MA milliamps
PCT percent
Table 2-6
- Type Suffixes for Flexible Combiner Constants
It is important to note that when type suffixes are used
that are different from the E2's internal SI values, they are
"converted" to the SI units behind the scenes. For exam-
ple, the equation "AI1+0.2BAR" actually adds 20,000 to
the raw value of AI1 (0.2 bars converted to pascals, or
20,000PA).
Type Suffixes for Temperature Offsets (DDF and DDC)
If you are using a constant in an equation that is being
used to offset the value of a temperature sensor, you must
use the delta degrees suffixes (DDF and DDC), not the
standard temperature suffixes (DF and DC). A constant
with a DF or DC suffix is interpreted as a literal tempera-
ture and converted before the math operation is performed,
so an equation like AI1+10DF is interpreted as "AI1 plus
the value of 10DF converted to Celsius (12.2)." The cor-
rect way to write this would be AI1+10DDF, which would
add 10°F to the value of AI1 before converting the entire
equation to SI units.
Use the DDF and DDC suffixes in every equation that
uses basic math in conjunction with temperature offsets.
2.2.3

Time Constants

Used in delay equations and pulse width (PW) equa-
tions, constants representing times of day or delay time
durations can be entered into equations in a variety of
ways:
• As a duration in HH:MM (hours/minutes).
Example: "01:45" sets the time delay to 1 hour, 45
minutes (6300 seconds).
• As a duration in HH:MM:SS (hours/minutes/
seconds). Example: "01:00:00" sets the time delay
to 1 hour (3600 seconds). Use this format for min-
Suffix Unit
DPA differential in
pascals
GAL gallons
L liters
CF cubic feet
CM cubic meter
CCF cubic centi-feet
CCFH cubic centi-feet
per hour
FT feet
M meters
• -
Constants 2 3