ABB COMMANDER 1900 Series User Manual page 21

...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:
M (lb/min) = 8.334 x Volume (gal/min) x
The example below shows the construction of Maths block 1 with the following selected:
• maths block function–
• input A source –
Process Variable 1
• input t source
Process Variable 2
• temperature units –
• temperature reference (process conditions using maximum flow rate) –
input P source –
• Process Variable 3
• pressure reference (process conditions using maximum flow rate) –
• scaling constant –
Function
Input A
Constant 8
Constant 1
Maths Block 4
Maths Block 1
Avarage
Input 6
Lo Value
Input 1
Hi Value
Channel 1/2 Output
Channel 1/2 Output
Mass 2
(cool)
Channel 1/2 Output
Mass 1
(heat)
RH
Process Variable 4
Process Variable 3
Std
Position F.B. 2
Off
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
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
measured pressure (p.s.i.a.)
14.69 p.s.i.a.
Mass 1
Deg F
8.334
Temperature
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
5 ADVANCED CONFIGURATION LEVEL...
x
measured temperature °R
60.0
14.69
Temperature
Units
Reference
Abs
Deg F
60.0
Deg C
(460 + 60)°R
Pressure
Input P
Reference
Constant 8
Constant 1
Maths Block 4
Maths Block 1
Input 6
Input 1
Channel 1/2 Output
Channel 1/2 Output
14.69
(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
NONE
• Maths
Scaling
Constant
8.334
.
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