Intek RheoVac 940 - Manual (Page 4)

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1.2 PRINCIPLE OF OPERATION
The principal features of the RheoVac monitor are shown in Figure 1. At the heart of the RheoVac
monitor is the Rheotherm flow transducer which uses the same patented thermal sensing technique
employed in all precision flow instruments manufactured by Intek. Two temperature sensor probes are
used — one sensor is in thermal equilibrium with the flow medium and provides a temperature and flow
signal reference, while the second sensor is located near a constant power probe heater so that its
temperature is always above that of the fluid. The temperature of the heated sensor will vary with the
stream velocity of the fluid. Hence, the measured temperature differential between the reference sensor
and heated sensor is a function of flow rate, which is approximately proportional to the logarithm of
mass flow rate (USPN 4,255,968).
The Rheotherm flow sensor is calibrated to measure the total mass flow of the water vapor/air mixture.
From the other three measurements, the RheoVac electronics converts the total mass flow signal from
the transducer into two components, air mass flow rate and water vapor mass flow rate. This unique
measurement method is disclosed in two separate patents (USPN 5,485,754 & 5,752,411).
The RheoVac monitor is fully calibrated in the factory under dynamic fluid conditions identical to those
within the power plant vacuum line. No field adjustments are required.
1.3 TECHNICAL SPECIFICATIONS
Primary Calibration Accuracy:
±1% of reading
Repeatability:
±0.5% of reading
Operating Temperature:
Electronics: ! 20 to 120°F
Transducer: 40 to 160°F
Never subject transducer to
temperatures above 210°F
Operating Pressure:
0 to 10 inches Hg absolute
Process Connection:
Hot tap assembly
(1½” thread-o-let must be welded to
pipe for hot tap installation)
Wetted Surface:
300 Series SS and engineering plastic
Local Display:
air in-leakage (SCFM)
Input Power:
115 Vac, 50/60 Hz (±15V)
230 Vac, 50/60 Hz (±15V)
Signal Output:
4/20 mA (for 10 parameters)
RS 232/422
Storage Temperature:
! 20 to 120°F
Storage Pressure:
15 psig (maximum)
1.4 PRECAUTIONS
• Read the entire manual before installing and operating the RheoVac monitor.
• Carefully select the best location for installation of the transducer probe. Adequate straight
run and freedom from standing water in the line are vital to achieving optimal performance
from the RheoVac monitor (See Figure 2).
• Use reasonable care in handling the transducer — the sensing components are delicate. Take
care not to bend the probes, damage the tips, or otherwise obstruct the sensing ports.