Warnings; Calibration Overview - Emerson Rosemount 644 Reference Manual

Section 5: Operation and Maintenance
April 2015
5.2.1

Warnings

Failure to follow these installation guidelines could result in death or
serious injury.
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Explosions could resultin death or serious injury.
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Process leaks could result in death or serious injury.
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Electrical shock could cause death or serious injury.
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5.3

Calibration overview

Calibrating the transmitter increases the measurement precision by allowing corrections to be
made to the factory-stored characterization curve by digitally altering the transmitter's
interpretation of the sensor input.
To understand calibration, it is necessary to understand that smart transmitters operate
differently from analog transmitters. An important difference is that smart transmitters are fac-
tory-characterized, meaning that they are shipped with a standard sensor curve stored in the
transmitter firmware. In operation, the transmitter uses this information to produce a process
variable output, in engineering units, dependent on the sensor input.
Calibration of the 644 may include the following procedures:
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Make sure only qualified personnel perform the installation.
Do not remove the connection head cover in explosive atmospheres when the
circuit is live.
Before connecting a Field Communicator in an explosive atmosphere, make sure the
instruments in the loop are installed in accordance with intrinsically safe or
non-incendive field wiring practices.
Verify that the operating atmosphere of the transmitter is consistent with the
appropriate hazardous locations certifications.
All connection head covers must be fully engaged to meet
explosion-proof requirements.
Do not remove the thermowell while in operation.
Install and tighten thermowells and sensors before applying pressure.
Use extreme caution when making contact with the leads and terminals.
Sensor Input Trim: digitally alter the transmitter's interpretation of the input signal
Transmitter Sensor Matching: generates a special custom curve to match that specific
sensor curve, as derived from the Callendar-Van Dusen constants
Output Trim: calibrates the transmitter to a 4–20 mA reference scale
Scaled Output Trim: calibrates the transmitter to a user-selectable reference scale.
Reference Manual
00809-0200-4728, Rev RA
Operation and Maintenance