ABB COMMANDER 1900 Series, Руководство пользователя

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20
…5 ADVANCED CONFIGURATION LEVEL
• Maths
…5.1.3 Mass Flow 1 and 2
Example B – calculating the mass flow of water from the volume flow.
At a temperature of 15.6
°
C (288.6K) and an absolute pressure of 1013.25 mbar, 1 liter of water has a mass of 1kg.
To calculate the mass flow of water from the volume flow the following settings are used:
PV1 – volume flow of water (liters/min)
PV2 – temperature of water (
°
C)
PV3 – pressure of water (mbar (abs))
PV4 – result of maths block 1 (kg/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 C
• temperature reference (process conditions using maximum flow rate) –
15.6
•
input P source –
Process Variable 3
• pressure reference (process conditions using maximum flow rate) –
1013
• scaling constant –
1.000
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
None
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
15.6
Pressure
Reference
1013 1.00
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 (mbar)
1013.25 mbar
288.6K
measured temperature K
x M (kg/min) = 1 x Volume (liters/min) x