Relative Humidity (Rh) - ABB COMMANDER 1900 Series User Manual

• Maths
...5 ADVANCED CONFIGURATION LEVEL

5.1.2 Relative Humidity (RH)

The relative humidity calculation requires two inputs, one from a wet-bulb sensor and one from a dry-bulb sensor. Both of these
inputs are configured as variables. RH tables are based on the use of an aspirated psychrometer having an air velocity of at least
11.5 feet per second or 3.5 meters per second across the bulb sensors.
Note. Inputs used for wet- and dry-bulb measurement must be in the ranges 32 to 212°F or 0 to 100°C .
5.1.3 Mass Flow 1 and 2
The two types of mass flow calculations available are as follows:
– applications where a volumetric flow meter is used to measure flow.
Mass Flow 1
– applications where a differential pressure transmitter is used to measure flow.
Mass Flow 2
The standard formula for mass flow 1 is as follows:
P T
r
M = k V
T P
r
where:
k = Scaling constant
V = Input a (input from volume flow source)
P = Pressure (pressure input source)
T = Temperature (temperature input source)
T = Reference temperature (for the scaling constant used)
r
P = Reference pressure (for the scaling constant used)
r
The temperature units used by the input source must be specified, since all calculations use absolute temperatures and
conversion is made if the input uses °F or °C.
The standard formula for mass flow 2 is as follows:
(i)
h P T
r
M = k
T P
r
where:
h = differential pressure head
Some differential pressure sensors incorporate a square root linearizer and therefore produce an output linear to flow. In these
instances no additional linearization within the C1900 is required. Where the input from the differential pressure sensor is linear
to differential pressure head the square root linearizer within the C1900, must be selected in the
,
Up Input Page BASIC CONFIGURATION LEVEL
Therefore the formula used internally within the C1900 is:
(ii)
P Tr
M = k a
T Pr
where:
a = linearized flow signal
The linearized flow signal is produced by the transmitter or derived from the signal linearized within the C1900.
18
.
frame in the
Linearizer Type Set