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i have height of stem drum level 1000mm.how i calculate the
DP transmitter
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Answer Posted / aftab ahmed mazari
1. Never use any one one port of transmitter at boiler
point and other to atmosphere. Never. It will make a
serious accident and also transmitter will never work.
2. Connect Hi side of DP transmitter at bottom point of
outlet from boiler and LO side of DP tranmitter at top side
of boiler point.
3. Also use condensation bottle at lo side of tranmitter
(top side of boiler point)
4. Suppose transmitter is almost same level of bottom point.
Now there are two methods of calibration:
Method No. 1
a. Do not open valves of boilers side.(Very Important).
just open both hi to atmosphere and fill water at low side
from top of dp transmitter.
b. Transmitter will show less mA as compare to 4 mA.
Suppose its showing 2 mA. Tranmitter zero elevated. Get
adjust 4 mA from HART.
c. Your range is 1000 mm. Usually specific gravity of
boiler water under temperature and pressure is 0.45. (It
depends upon boiler pressure and temperature).
d. So get range = 1000 x 0.45 = 450 mm of H2O. It is that
type of transmitter which did its zero by HART.So adjust 20
mA by feeding pressure of 450 mm of H2O.
e. Get connect piping of transmitter to sensing lines and
put in service the transmitter.
Another method is, you want to calibrate it at work shop
without using HART.
a. Usually water specific density/gravity at upper side
after getting out from boiler drum and being condensated in
pipe of transmitter is 0.99.
4 mA = 1000 x 0.99 = 990 mm H2O
It will be written as - 990 mm H2O.
b. Give pressure at lower side of dp transmitter 990 mm H2O
and transmitter Hi side must be opened to atmosphere.
c. Get adjust transmitter 4 mA.
d. 20 mA range = 1000 x .45 = 450 mm H2O
e. Apply 450 mm H2O pressure at Hi side of transmitter and
adjust 20 mA signal from range knob. Remember not to
disconnect lo side pressure.
Suppose, you want to calibrate from lo side only.
a. At 990 mm of H2O low side = 4 mA
b. Decrease the pressure from 990 to 540 mm of H2O (990 -
450 = 540) from low side, you will get 20 mA.
Note: If you put transmitter hi side connected to boiler
and low side to atmmsphere, DP transmitter will burst.
Becareful.
aftabmazari@yahoo.com
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