Sage Prime SIP Series, Руководство по эксплуатации и инструкция

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S A G E M E T E R I N G , I N C .
O p e r a t i o n s a n d I n s t r u c t i o n M a n u a l
68
REV. 16-SIP/SRP
What is a Thermal Mass Flow Meter?
FLOW SENSOR
(Self Heated)
TEMPERATURE SENSOR
(Reference Sensor)
• What is a Thermal Mass Flow Meter? It is a meter
that directly measures the gas mass flow based
on the principle of conductive and convective
heat transfer.
• All Meters have probes (Insertion Style) or Flow
Bodies (In-Line Style) that support a pair of
sensors, which are in contact with the gas.
• The sensors are RTDs, which are resistance tem -
perature detectors. They consist of highly stable
reference-grade platinum windings. In fact, we
use the same material that is used as Platinum
Resistance Standards at the NIST.
• The RTDs are clad in a protective 316 SS sheath
for industrial environments.
• One of the RTDs [See Diagram below] is self-heated
by the circuitry and serves as the flow sensor. The
other RTD acts as a reference sensor, and measures
the gas temperature. Essen tial ly it is used for tem-
perature compensation.
• The Sage proprietary hybrid-digital sensor drive
circuitry maintains a constant overheat between
the flow sensor and the reference sensor. As gas
flows by the heated sensor (flow sensor), the
molecules of flowing gas carry heat away from
this sensor, and the sensor cools down as it loses
energy. The circuit equilibrium is disturbed, and
momentarily the temperature difference between
the heated sensor and the reference sensor has
changed. The circuit will automatically (within
1 second) replace this lost energy by heating
up the flow sensor so the overheat temperature
is restored.
• The current required to maintain this overheat
represents the mass flow signal. There is no need
for external temperature or pressure devices.