Emerson Rosemount 644h, Reference Manual

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Reference Manual
00809-0100-4728, Rev HA
December 2002
2-15
Models 644H and 644R
COMMISSIONING
Failure Mode
As part of normal operation, each transmitter continuously monitors its own
performance. This automatic diagnostics routine is a timed series of checks
repeated continuously. If diagnostics detect an input sensor failure or a failure
in the transmitter electronics, the transmitter drives its output to low or high
depending on the position of the failure mode switch. Saturation levels are
3.90 mA for standard configuration (3.8 mA if configured for NAMUR-
compliant operation) on the low end and 20.5 mA for standard or NAMUR-
compliant configuration on the high end, if the sensor temperature is outside
of range limits. These values are also custom configurable by the factory or
using the Model 275 HART Communicator.
The values to which the transmitter drives its output in failure mode depend
on whether it is configured to standard, NAMUR-compliant, or custom
operation. See “Hardware and Software Failure Mode” on page A-2 for
standard and NAMUR-compliant operation parameters.
Changing Switch
Positions
To change the failure mode on the Model 644H or 644R transmitter, follow the
steps described below.
1. If applicable, remove the enclosure cover.
2. Locate the orange failure mode switch. On the Model 644H the switch
is located near the power terminals and located in the center of the
front panel on the Model 644R (see Figure 2-6).
3. Move the switch to the desired alarm setting. To set the failure mode
to high alarm, position the switch toward the “HI” mark on the terminal
block. To set the failure mode to low alarm, position the switch in the
opposite direction.
4. Replace the enclosure cover (if applicable). Enclosure covers must
be fully engaged to meet explosion-proof requirements.