Intek RheoVac DR - Manual (Page 4)

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1.2 PRINCIPLE OF OPERATION
The principal features of the RheoVac DR system are shown in Figure 1. At the heart of the RheoVac
DR 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 water vapor/air mixture.
From the other three measurements - temperature, pressure and relative saturation - the RheoVac DR
electronics converts the total 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 DR system is fully calibrated in the factory under dynamic fluid conditions similar to those
within the dryer vacuum line. Typically, field adjustments are not required.
1.3 TECHNICAL SPECIFICATIONS
1.3.1 Sensor (Probe) Specifications
Primary Calibration Accuracy:
±5% of total mass flow
Repeatability:
±0.5% of reading
Operating Temperature:
Electronics: 40 to 120ºF (5 to 49ºC)
Probe: 40 to 160ºF (5 to 71ºC)
Never subject probe to temperatures above 210ºF (99ºC)
Operating Pressure:
0.5 to 30 inches Hg absolute
15 psi maximum
Storage Temperature:
-20 to 210ºF (-29 to 99ºC)
Storage Pressure:
15 psig (maximum)
Process Connection:
NPT
Hot tap assembly (optional, 1½” thread-o-let must be welded to pipe for
hot tap installation)
Wetted Surface:
300 Series SS and engineered plastic