ABB COMMANDER 1900 Series, User Manual, Page: 21 / 36

19
5 ADVANCED CONFIGURATION LEVEL…
• Maths
…5.1.3 Mass Flow 1 and 2
Example A – calculating the mass flow of water from the volume flow.
At a temperature of 60
°
F (520
°
R) and an absolute pressure of 14.696 p.s.i.a., 1 gallon (US) of water has a mass of 8.334 lbs.
To calculate the mass flow of water from the volume flow the following settings are used:
PV1 – volume flow of water (gal/min)
PV2 – temperature of water (
°
F)
PV3 – pressure of water (p.s.i.a.)
PV4 – result of maths block 1 (lb/min)
therefore the equation is:
The example below shows the construction of Maths block 1 with the following selected:
• maths block function–
Mass 1
• input A source –
Process Variable 1
• input t source
Process Variable 2
• temperature units –
Deg F
• temperature reference (process conditions using maximum flow rate) –
60.0
•
input P source –
Process Variable 3
• pressure reference (process conditions using maximum flow rate) –
14.69
• scaling constant –
8.334
Function
Constant 8
Constant 1
Maths Block 4
Maths Block 1
Input 6
Input 1
Channel 1/2 Output
Channel 1/2 Output
(cool)
Channel 1/2 Output
(heat)
Process Variable 4
Process Variable 3
Position F.B. 2
Remote S.P. 2
Local S.P. 2
Process Variable 2
Position F.B. 1
Remote S.P. 1
Local S.P. 1
Process Variable 1
Input A Input t
Constant 8
Constant 1
Maths Block 4
Maths Block 1
Input 6
Input 1
Channel 1/2 Output
Channel 1/2 Output
(cool)
Channel 1/2 Output
(heat)
Process Variable 4
Process Variable 3
Position F.B. 2
Remote S.P. 2
Local S.P. 2
Process Variable 2
Position F.B. 1
Remote S.P. 1
Local S.P. 1
Process Variable 1
None
Temperature
Reference
Input P
Constant 8
Constant 1
Maths Block 4
Maths Block 1
Input 6
Input 1
Channel 1/2 Output
Channel 1/2 Output
(cool)
Channel 1/2 Output
(heat)
Process Variable 4
Process Variable 3
Position F.B. 2
Remote S.P. 2
Local S.P. 2
Process Variable 2
Position F.B. 1
Remote S.P. 1
Local S.P. 1
Process Variable 1
None
Temperature
Units
Avarage
Lo Value
Hi Value
Mass 2
Mass 1
RH
Std
Off
Abs
Deg F
Deg C
60.0
Pressure
Reference
14.69 8.334
Scaling
Constant
Note.
• It is imperative that the temperature input/temperature reference have the same units and the pressure input/pressure
reference have the same absolute units.
• The basic mass flow equation must use absolute temperatures (K or
°
R). The C1900 converts automatically from
°
C
or
°
F to absolute.
• If temperature or pressure correction is not required the temperature or pressure inputs can be set to NONE .
measured pressure (p.s.i.a.)
14.69 p.s.i.a.
(460 + 60)
°
R
measured temperature
°
R
x M (lb/min) = 8.334 x Volume (gal/min) x