Welcome
Thank you for purchasing the TM500 Thermal Gas Mass Flow Meter from Sierra Instruments. The
TM500 is one of the most technically advanced flow meters in the world. Extensive engineering
eort has been invested to deliver advanced features, accurate measurement performance and
outstanding reliability.
This instruction manual contains the electrical and mechanical installation instructions as well as
details for programming, maintaining and troubleshooting the meter. This manual is divided into
the following sections: Introduction, Installation, Wiring, Operation, Communications, Maintenance,
Appendices, Definitions, and Index.
Theory of Operation
The TM500 is an innovative thermal mass gas flow meter and temperature transmitter. It is
microprocessor-based and field programmable. The TM500 thermal sensor operates on the law
that gases absorb heat. A heated sensor placed in an air or gas stream transfers heat in proportion
to the stream’s mass velocity. There are two sensor elements. One sensor element detects the
gas temperature and a second element is maintained at a constant temperature above the gas
temperature. The energy transferred from the heated element is proportional to the mass flow
velocity. The TM500 flow meter maintains accurate flow measurement over a large temperature and
pressure range.
Mass Flow
The TM500 measures mass flow; an advantage over other flow meters which measure volumetric
flow rate. Volumetric flow is incomplete because temperature and pressure are unknown and
must be measured separately. For example, the mass flow of a gas depends on its temperature
and pressure. As temperature and pressure changes, the gas volume changes but not its mass.
Therefore a device measuring mass flow is independent of temperature and pressure changes. The
TM500 provides a direct measurement of gas flow in Mass units (kg/hr, lb/hr), standard units (SCFM,
SLPM) or normal units (NM3/hr, NLPM) with no additional temperature or pressure measurements
required.
Calibration Validation
Validate the calibration of the TM500 in the field using the TM-Cal™ test. The goal of Calibration
Validation is to provide operators with the ability to verify that the meter is capturing accurate data
at scheduled recalibration times - or at any time - instead of sending the meter back to the factory
for recalibration. By performing TM-Cal™ in the field, operators can verify that the meter is running
accurately by testing the functionality of the sensor and its associated signal processing circuitry.
This test can be done in the pipe under normal process conditions.
TM500
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Introduction