Intek RheoVac 950 - Manual (Page 4)

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1.2 PRINCIPLE OF OPERATION
The principal features of the RheoVac system are shown in Figure 1. At the heart of the RheoVac
system is the Rheotherm mass flow transducer, which uses the same patented thermal sensing technique
employed in all precision flow instruments manufactured by Intek. Two temperature sensors 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 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 gaseous water vapor/air
mixture. From the other three measurements, the RheoVac electronics converts the total gas mass flow
signal from the probe 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 system 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:
±5% Total Mass Flow
Repeatability:
±0.5% of reading
Operating Temperature:
Electronics: 40 to 120°F (5 to 49°C)
Probe: 40 to 160°F (5 to 71°C)
Never subject probe to temperatures
above 210°F (99°C)
Operating Pressure:
0.5 to 30 inches Hg absolute
15 psi maximum
Process Connection:
Hot tap assembly
(1½” thread-o-let must be welded to
pipe for hot tap installation)
Wetted Surface:
300 Series SS and engineered plastic
Local Display:
Back-lit LCD
Selectable display of air in-leakage and 6
of the other output parameters
Input Power:
100-250 Vac, 50/60 Hz
Signal Output:
RS-232/RS-422/Serial Modbus, Ethernet
Eight 4-20mA signals (optional)
Data Access:
Ethernet
Storage Temperature:
! 20 to 120°F (-29 to 49°C)
Storage Pressure:
15 psig (maximum)
Local Keypad:
Parameter scrolling
Metric/English units
1.4 PRECAUTIONS
Read the entire manual before installing and operating the RheoVac system.
Carefully select the best locations for installation of the probes. Access, installation clearances,
freedom from standing water, and straight-run should all be considered when selecting a probe
location.